external/bsd/bind/dist/doc/arm/Bv9ARM.ch06.html
author bouyer <bouyer@NetBSD.org>
Sun, 15 Nov 2015 19:17:51 +0000
branchnetbsd-6-1
changeset 277127 23d5207bb72e
parent 277086 83c07c604c12
child 257482 2be21b9dcdf6
child 277140 9f93d5820486
permissions -rw-r--r--
Apply patch, requested by spz in ticket 1329: Update bind to 9.9.7-P3

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<div class="titlepage"><div><div><h2 class="title">
<a name="Bv9ARM.ch06"></a>Chapter 6. <acronym class="acronym">BIND</acronym> 9 Configuration Reference</h2></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl>
<dt><span class="sect1"><a href="Bv9ARM.ch06.html#configuration_file_elements">Configuration File Elements</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#address_match_lists">Address Match Lists</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2573374">Comment Syntax</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="Bv9ARM.ch06.html#Configuration_File_Grammar">Configuration File Grammar</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2574035"><span><strong class="command">acl</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#acl"><span><strong class="command">acl</strong></span> Statement Definition and
          Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2574225"><span><strong class="command">controls</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#controls_statement_definition_and_usage"><span><strong class="command">controls</strong></span> Statement Definition and
          Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2574584"><span><strong class="command">include</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2574601"><span><strong class="command">include</strong></span> Statement Definition and
          Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2574761"><span><strong class="command">key</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2574785"><span><strong class="command">key</strong></span> Statement Definition and Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2574875"><span><strong class="command">logging</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2575001"><span><strong class="command">logging</strong></span> Statement Definition and
          Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2577168"><span><strong class="command">lwres</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2577241"><span><strong class="command">lwres</strong></span> Statement Definition and Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2577305"><span><strong class="command">masters</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2577417"><span><strong class="command">masters</strong></span> Statement Definition and
          Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2577438"><span><strong class="command">options</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#options"><span><strong class="command">options</strong></span> Statement Definition and
          Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#server_statement_grammar"><span><strong class="command">server</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#server_statement_definition_and_usage"><span><strong class="command">server</strong></span> Statement Definition and
            Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#statschannels"><span><strong class="command">statistics-channels</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2590489"><span><strong class="command">statistics-channels</strong></span> Statement Definition and
            Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#trusted-keys"><span><strong class="command">trusted-keys</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2590796"><span><strong class="command">trusted-keys</strong></span> Statement Definition
            and Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2590843"><span><strong class="command">managed-keys</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#managed-keys"><span><strong class="command">managed-keys</strong></span> Statement Definition
            and Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#view_statement_grammar"><span><strong class="command">view</strong></span> Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2591278"><span><strong class="command">view</strong></span> Statement Definition and Usage</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#zone_statement_grammar"><span><strong class="command">zone</strong></span>
            Statement Grammar</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2592987"><span><strong class="command">zone</strong></span> Statement Definition and Usage</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="Bv9ARM.ch06.html#id2596605">Zone File</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#types_of_resource_records_and_when_to_use_them">Types of Resource Records and When to Use Them</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2598768">Discussion of MX Records</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#Setting_TTLs">Setting TTLs</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2599451">Inverse Mapping in IPv4</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2599578">Other Zone File Directives</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#id2599851"><acronym class="acronym">BIND</acronym> Master File Extension: the  <span><strong class="command">$GENERATE</strong></span> Directive</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch06.html#zonefile_format">Additional File Formats</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="Bv9ARM.ch06.html#statistics">BIND9 Statistics</a></span></dt>
<dd><dl><dt><span class="sect2"><a href="Bv9ARM.ch06.html#statistics_counters">Statistics Counters</a></span></dt></dl></dd>
</dl>
</div>
<p>
      <acronym class="acronym">BIND</acronym> 9 configuration is broadly similar
      to <acronym class="acronym">BIND</acronym> 8; however, there are a few new
      areas
      of configuration, such as views. <acronym class="acronym">BIND</acronym>
      8 configuration files should work with few alterations in <acronym class="acronym">BIND</acronym>
      9, although more complex configurations should be reviewed to check
      if they can be more efficiently implemented using the new features
      found in <acronym class="acronym">BIND</acronym> 9.
    </p>
<p>
      <acronym class="acronym">BIND</acronym> 4 configuration files can be
      converted to the new format
      using the shell script
      <code class="filename">contrib/named-bootconf/named-bootconf.sh</code>.
    </p>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="configuration_file_elements"></a>Configuration File Elements</h2></div></div></div>
<p>
        Following is a list of elements used throughout the <acronym class="acronym">BIND</acronym> configuration
        file documentation:
      </p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                <p>
                  <code class="varname">acl_name</code>
                </p>
              </td>
<td>
                <p>
                  The name of an <code class="varname">address_match_list</code> as
                  defined by the <span><strong class="command">acl</strong></span> statement.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">address_match_list</code>
                </p>
              </td>
<td>
                <p>
                  A list of one or more
                  <code class="varname">ip_addr</code>,
                  <code class="varname">ip_prefix</code>, <code class="varname">key_id</code>,
                  or <code class="varname">acl_name</code> elements, see
                  <a href="Bv9ARM.ch06.html#address_match_lists" title="Address Match Lists">the section called &#8220;Address Match Lists&#8221;</a>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">masters_list</code>
                </p>
              </td>
<td>
                <p>
                  A named list of one or more <code class="varname">ip_addr</code>
                  with optional <code class="varname">key_id</code> and/or
                  <code class="varname">ip_port</code>.
                  A <code class="varname">masters_list</code> may include other
                  <code class="varname">masters_lists</code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">domain_name</code>
                </p>
              </td>
<td>
                <p>
                  A quoted string which will be used as
                  a DNS name, for example "<code class="literal">my.test.domain</code>".
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">namelist</code>
                </p>
              </td>
<td>
                <p>
                  A list of one or more <code class="varname">domain_name</code>
                  elements.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">dotted_decimal</code>
                </p>
              </td>
<td>
                <p>
                  One to four integers valued 0 through
                  255 separated by dots (`.'), such as <span><strong class="command">123</strong></span>,
                  <span><strong class="command">45.67</strong></span> or <span><strong class="command">89.123.45.67</strong></span>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">ip4_addr</code>
                </p>
              </td>
<td>
                <p>
                  An IPv4 address with exactly four elements
                  in <code class="varname">dotted_decimal</code> notation.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">ip6_addr</code>
                </p>
              </td>
<td>
                <p>
                  An IPv6 address, such as <span><strong class="command">2001:db8::1234</strong></span>.
                  IPv6 scoped addresses that have ambiguity on their
                  scope zones must be disambiguated by an appropriate
                  zone ID with the percent character (`%') as
                  delimiter.  It is strongly recommended to use
                  string zone names rather than numeric identifiers,
                  in order to be robust against system configuration
                  changes.  However, since there is no standard
                  mapping for such names and identifier values,
                  currently only interface names as link identifiers
                  are supported, assuming one-to-one mapping between
                  interfaces and links.  For example, a link-local
                  address <span><strong class="command">fe80::1</strong></span> on the link
                  attached to the interface <span><strong class="command">ne0</strong></span>
                  can be specified as <span><strong class="command">fe80::1%ne0</strong></span>.
                  Note that on most systems link-local addresses
                  always have the ambiguity, and need to be
                  disambiguated.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">ip_addr</code>
                </p>
              </td>
<td>
                <p>
                  An <code class="varname">ip4_addr</code> or <code class="varname">ip6_addr</code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">ip_port</code>
                </p>
              </td>
<td>
                <p>
                  An IP port <code class="varname">number</code>.
                  The <code class="varname">number</code> is limited to 0
                  through 65535, with values
                  below 1024 typically restricted to use by processes running
                  as root.
                  In some cases, an asterisk (`*') character can be used as a
                  placeholder to
                  select a random high-numbered port.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">ip_prefix</code>
                </p>
              </td>
<td>
                <p>
                  An IP network specified as an <code class="varname">ip_addr</code>,
                  followed by a slash (`/') and then the number of bits in the
                  netmask.
                  Trailing zeros in a <code class="varname">ip_addr</code>
                  may omitted.
                  For example, <span><strong class="command">127/8</strong></span> is the
                  network <span><strong class="command">127.0.0.0</strong></span> with
                  netmask <span><strong class="command">255.0.0.0</strong></span> and <span><strong class="command">1.2.3.0/28</strong></span> is
                  network <span><strong class="command">1.2.3.0</strong></span> with netmask <span><strong class="command">255.255.255.240</strong></span>.
                </p>
                <p>
                  When specifying a prefix involving a IPv6 scoped address
                  the scope may be omitted.  In that case the prefix will
                  match packets from any scope.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">key_id</code>
                </p>
              </td>
<td>
                <p>
                  A <code class="varname">domain_name</code> representing
                  the name of a shared key, to be used for transaction
                  security.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">key_list</code>
                </p>
              </td>
<td>
                <p>
                  A list of one or more
                  <code class="varname">key_id</code>s,
                  separated by semicolons and ending with a semicolon.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">number</code>
                </p>
              </td>
<td>
                <p>
                  A non-negative 32-bit integer
                  (i.e., a number between 0 and 4294967295, inclusive).
                  Its acceptable value might further
                  be limited by the context in which it is used.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">path_name</code>
                </p>
              </td>
<td>
                <p>
                  A quoted string which will be used as
                  a pathname, such as <code class="filename">zones/master/my.test.domain</code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">port_list</code>
                </p>
              </td>
<td>
                <p>
                  A list of an <code class="varname">ip_port</code> or a port
                  range.
                  A port range is specified in the form of
                  <strong class="userinput"><code>range</code></strong> followed by
                  two <code class="varname">ip_port</code>s,
                  <code class="varname">port_low</code> and
                  <code class="varname">port_high</code>, which represents
                  port numbers from <code class="varname">port_low</code> through
                  <code class="varname">port_high</code>, inclusive.
                  <code class="varname">port_low</code> must not be larger than
                  <code class="varname">port_high</code>.
                  For example,
                  <strong class="userinput"><code>range 1024 65535</code></strong> represents
                  ports from 1024 through 65535.
                  In either case an asterisk (`*') character is not
                  allowed as a valid <code class="varname">ip_port</code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">size_spec</code>
                </p>
              </td>
<td>
                <p>
                  A 64-bit unsigned integer, or the keywords
                  <strong class="userinput"><code>unlimited</code></strong> or
                  <strong class="userinput"><code>default</code></strong>.
                </p>
                <p>
                  Integers may take values
                  0 &lt;= value &lt;= 18446744073709551615, though
                  certain parameters
                  (such as <span><strong class="command">max-journal-size</strong></span>) may
                  use a more limited range within these extremes.
                  In most cases, setting a value to 0 does not
                  literally mean zero; it means "undefined" or
                  "as big as possible", depending on the context.
                  See the explanations of particular parameters
                  that use <code class="varname">size_spec</code>
                  for details on how they interpret its use. 
                </p>
                <p>
                  Numeric values can optionally be followed by a
                  scaling factor:
                  <strong class="userinput"><code>K</code></strong> or <strong class="userinput"><code>k</code></strong>
                  for kilobytes,
                  <strong class="userinput"><code>M</code></strong> or <strong class="userinput"><code>m</code></strong>
                  for megabytes, and
                  <strong class="userinput"><code>G</code></strong> or <strong class="userinput"><code>g</code></strong>
                  for gigabytes, which scale by 1024, 1024*1024, and
                  1024*1024*1024 respectively.
                </p>
                <p>
                  <code class="varname">unlimited</code> generally means
                  "as big as possible", though in certain contexts,
                  (including <code class="option">max-cache-size</code>), it may
                  mean the largest possible 32-bit unsigned integer
                  (0xffffffff); this distinction can be important when
                  dealing with larger quantities. 
                  <code class="varname">unlimited</code> is usually the best way
                  to safely set a very large number.
                </p>
                <p>
                  <code class="varname">default</code> 
                  uses the limit that was in force when the server was started.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">yes_or_no</code>
                </p>
              </td>
<td>
                <p>
                  Either <strong class="userinput"><code>yes</code></strong> or <strong class="userinput"><code>no</code></strong>.
                  The words <strong class="userinput"><code>true</code></strong> and <strong class="userinput"><code>false</code></strong> are
                  also accepted, as are the numbers <strong class="userinput"><code>1</code></strong>
                  and <strong class="userinput"><code>0</code></strong>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="varname">dialup_option</code>
                </p>
              </td>
<td>
                <p>
                  One of <strong class="userinput"><code>yes</code></strong>,
                  <strong class="userinput"><code>no</code></strong>, <strong class="userinput"><code>notify</code></strong>,
                  <strong class="userinput"><code>notify-passive</code></strong>, <strong class="userinput"><code>refresh</code></strong> or
                  <strong class="userinput"><code>passive</code></strong>.
                  When used in a zone, <strong class="userinput"><code>notify-passive</code></strong>,
                  <strong class="userinput"><code>refresh</code></strong>, and <strong class="userinput"><code>passive</code></strong>
                  are restricted to slave and stub zones.
                </p>
              </td>
</tr>
</tbody>
</table></div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="address_match_lists"></a>Address Match Lists</h3></div></div></div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2573073"></a>Syntax</h4></div></div></div>
<pre class="programlisting"><code class="varname">address_match_list</code> = address_match_list_element ;
  [<span class="optional"> address_match_list_element; ... </span>]
<code class="varname">address_match_list_element</code> = [<span class="optional"> ! </span>] (ip_address [<span class="optional">/length</span>] |
   key key_id | acl_name | { address_match_list } )
</pre>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2573100"></a>Definition and Usage</h4></div></div></div>
<p>
            Address match lists are primarily used to determine access
            control for various server operations. They are also used in
            the <span><strong class="command">listen-on</strong></span> and <span><strong class="command">sortlist</strong></span>
            statements. The elements which constitute an address match
            list can be any of the following:
          </p>
<div class="itemizedlist"><ul type="disc">
<li>an IP address (IPv4 or IPv6)</li>
<li>an IP prefix (in `/' notation)</li>
<li>
                a key ID, as defined by the <span><strong class="command">key</strong></span>
                statement
              </li>
<li>the name of an address match list defined with
                the <span><strong class="command">acl</strong></span> statement
              </li>
<li>a nested address match list enclosed in braces</li>
</ul></div>
<p>
            Elements can be negated with a leading exclamation mark (`!'),
            and the match list names "any", "none", "localhost", and
            "localnets" are predefined. More information on those names
            can be found in the description of the acl statement.
          </p>
<p>
            The addition of the key clause made the name of this syntactic
            element something of a misnomer, since security keys can be used
            to validate access without regard to a host or network address.
            Nonetheless, the term "address match list" is still used
            throughout the documentation.
          </p>
<p>
            When a given IP address or prefix is compared to an address
            match list, the comparison takes place in approximately O(1)
            time.  However, key comparisons require that the list of keys
            be traversed until a matching key is found, and therefore may
            be somewhat slower.
          </p>
<p>
            The interpretation of a match depends on whether the list is being
            used for access control, defining <span><strong class="command">listen-on</strong></span> ports, or in a
            <span><strong class="command">sortlist</strong></span>, and whether the element was negated.
          </p>
<p>
            When used as an access control list, a non-negated match
            allows access and a negated match denies access. If
            there is no match, access is denied. The clauses
            <span><strong class="command">allow-notify</strong></span>,
            <span><strong class="command">allow-recursion</strong></span>,
            <span><strong class="command">allow-recursion-on</strong></span>,
            <span><strong class="command">allow-query</strong></span>,
            <span><strong class="command">allow-query-on</strong></span>,
            <span><strong class="command">allow-query-cache</strong></span>,
            <span><strong class="command">allow-query-cache-on</strong></span>,
            <span><strong class="command">allow-transfer</strong></span>,
            <span><strong class="command">allow-update</strong></span>,
            <span><strong class="command">allow-update-forwarding</strong></span>, and
            <span><strong class="command">blackhole</strong></span> all use address match
            lists.  Similarly, the <span><strong class="command">listen-on</strong></span> option will cause the
            server to refuse queries on any of the machine's
            addresses which do not match the list.
          </p>
<p>
            Order of insertion is significant.  If more than one element
            in an ACL is found to match a given IP address or prefix,
            preference will be given to the one that came
            <span class="emphasis"><em>first</em></span> in the ACL definition.
            Because of this first-match behavior, an element that
            defines a subset of another element in the list should
            come before the broader element, regardless of whether
            either is negated. For example, in
            <span><strong class="command">1.2.3/24; ! 1.2.3.13;</strong></span>
            the 1.2.3.13 element is completely useless because the
            algorithm will match any lookup for 1.2.3.13 to the 1.2.3/24
            element.  Using <span><strong class="command">! 1.2.3.13; 1.2.3/24</strong></span> fixes
            that problem by having 1.2.3.13 blocked by the negation, but
            all other 1.2.3.* hosts fall through.
          </p>
</div>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2573374"></a>Comment Syntax</h3></div></div></div>
<p>
          The <acronym class="acronym">BIND</acronym> 9 comment syntax allows for
          comments to appear
          anywhere that whitespace may appear in a <acronym class="acronym">BIND</acronym> configuration
          file. To appeal to programmers of all kinds, they can be written
          in the C, C++, or shell/perl style.
        </p>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2573458"></a>Syntax</h4></div></div></div>
<p>
            </p>
<pre class="programlisting">/* This is a <acronym class="acronym">BIND</acronym> comment as in C */</pre>
<p>
            </p>
<pre class="programlisting">// This is a <acronym class="acronym">BIND</acronym> comment as in C++</pre>
<p>
            </p>
<pre class="programlisting"># This is a <acronym class="acronym">BIND</acronym> comment as in common UNIX shells
# and perl</pre>
<p>
          </p>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2573488"></a>Definition and Usage</h4></div></div></div>
<p>
            Comments may appear anywhere that whitespace may appear in
            a <acronym class="acronym">BIND</acronym> configuration file.
          </p>
<p>
            C-style comments start with the two characters /* (slash,
            star) and end with */ (star, slash). Because they are completely
            delimited with these characters, they can be used to comment only
            a portion of a line or to span multiple lines.
          </p>
<p>
            C-style comments cannot be nested. For example, the following
            is not valid because the entire comment ends with the first */:
          </p>
<p>

</p>
<pre class="programlisting">/* This is the start of a comment.
   This is still part of the comment.
/* This is an incorrect attempt at nesting a comment. */
   This is no longer in any comment. */
</pre>
<p>

          </p>
<p>
            C++-style comments start with the two characters // (slash,
            slash) and continue to the end of the physical line. They cannot
            be continued across multiple physical lines; to have one logical
            comment span multiple lines, each line must use the // pair.
            For example:
          </p>
<p>

</p>
<pre class="programlisting">// This is the start of a comment.  The next line
// is a new comment, even though it is logically
// part of the previous comment.
</pre>
<p>

          </p>
<p>
            Shell-style (or perl-style, if you prefer) comments start
            with the character <code class="literal">#</code> (number sign)
            and continue to the end of the
            physical line, as in C++ comments.
            For example:
          </p>
<p>

</p>
<pre class="programlisting"># This is the start of a comment.  The next line
# is a new comment, even though it is logically
# part of the previous comment.
</pre>
<p>

          </p>
<div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Warning</h3>
<p>
              You cannot use the semicolon (`;') character
              to start a comment such as you would in a zone file. The
              semicolon indicates the end of a configuration
              statement.
            </p>
</div>
</div>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="Configuration_File_Grammar"></a>Configuration File Grammar</h2></div></div></div>
<p>
        A <acronym class="acronym">BIND</acronym> 9 configuration consists of
        statements and comments.
        Statements end with a semicolon. Statements and comments are the
        only elements that can appear without enclosing braces. Many
        statements contain a block of sub-statements, which are also
        terminated with a semicolon.
      </p>
<p>
        The following statements are supported:
      </p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                <p><span><strong class="command">acl</strong></span></p>
              </td>
<td>
                <p>
                  defines a named IP address
                  matching list, for access control and other uses.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">controls</strong></span></p>
              </td>
<td>
                <p>
                  declares control channels to be used
                  by the <span><strong class="command">rndc</strong></span> utility.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">include</strong></span></p>
              </td>
<td>
                <p>
                  includes a file.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">key</strong></span></p>
              </td>
<td>
                <p>
                  specifies key information for use in
                  authentication and authorization using TSIG.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">logging</strong></span></p>
              </td>
<td>
                <p>
                  specifies what the server logs, and where
                  the log messages are sent.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">lwres</strong></span></p>
              </td>
<td>
                <p>
                  configures <span><strong class="command">named</strong></span> to
                  also act as a light-weight resolver daemon (<span><strong class="command">lwresd</strong></span>).
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">masters</strong></span></p>
              </td>
<td>
                <p>
                  defines a named masters list for
                  inclusion in stub and slave zones'
                  <span><strong class="command">masters</strong></span> or 
                  <span><strong class="command">also-notify</strong></span> lists.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">options</strong></span></p>
              </td>
<td>
                <p>
                  controls global server configuration
                  options and sets defaults for other statements.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">server</strong></span></p>
              </td>
<td>
                <p>
                  sets certain configuration options on
                  a per-server basis.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">statistics-channels</strong></span></p>
              </td>
<td>
                <p>
                  declares communication channels to get access to
                  <span><strong class="command">named</strong></span> statistics.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">trusted-keys</strong></span></p>
              </td>
<td>
                <p>
                  defines trusted DNSSEC keys.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">managed-keys</strong></span></p>
              </td>
<td>
                <p>
                  lists DNSSEC keys to be kept up to date
                  using RFC 5011 trust anchor maintenance.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">view</strong></span></p>
              </td>
<td>
                <p>
                  defines a view.
                </p>
              </td>
</tr>
<tr>
<td>
                <p><span><strong class="command">zone</strong></span></p>
              </td>
<td>
                <p>
                  defines a zone.
                </p>
              </td>
</tr>
</tbody>
</table></div>
<p>
        The <span><strong class="command">logging</strong></span> and
        <span><strong class="command">options</strong></span> statements may only occur once
        per
        configuration.
      </p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574035"></a><span><strong class="command">acl</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span><strong class="command">acl</strong></span> acl-name {
    address_match_list
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="acl"></a><span><strong class="command">acl</strong></span> Statement Definition and
          Usage</h3></div></div></div>
<p>
          The <span><strong class="command">acl</strong></span> statement assigns a symbolic
          name to an address match list. It gets its name from a primary
          use of address match lists: Access Control Lists (ACLs).
        </p>
<p>
          The following ACLs are built-in:
        </p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                  <p><span><strong class="command">any</strong></span></p>
                </td>
<td>
                  <p>
                    Matches all hosts.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p><span><strong class="command">none</strong></span></p>
                </td>
<td>
                  <p>
                    Matches no hosts.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p><span><strong class="command">localhost</strong></span></p>
                </td>
<td>
                  <p>
                    Matches the IPv4 and IPv6 addresses of all network
                    interfaces on the system.  When addresses are
                    added or removed, the <span><strong class="command">localhost</strong></span>
                    ACL element is updated to reflect the changes.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p><span><strong class="command">localnets</strong></span></p>
                </td>
<td>
                  <p>
                    Matches any host on an IPv4 or IPv6 network
                    for which the system has an interface.
                    When addresses are added or removed,
                    the <span><strong class="command">localnets</strong></span>
                    ACL element is updated to reflect the changes.
                    Some systems do not provide a way to determine the prefix
                    lengths of
                    local IPv6 addresses.
                    In such a case, <span><strong class="command">localnets</strong></span>
                    only matches the local
                    IPv6 addresses, just like <span><strong class="command">localhost</strong></span>.
                  </p>
                </td>
</tr>
</tbody>
</table></div>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574225"></a><span><strong class="command">controls</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span><strong class="command">controls</strong></span> {
   [ inet ( ip_addr | * ) [ port ip_port ]
                allow { <em class="replaceable"><code> address_match_list </code></em> }
                keys { <em class="replaceable"><code>key_list</code></em> }; ]
   [ inet ...; ]
   [ unix <em class="replaceable"><code>path</code></em> perm <em class="replaceable"><code>number</code></em> owner <em class="replaceable"><code>number</code></em> group <em class="replaceable"><code>number</code></em>
     keys { <em class="replaceable"><code>key_list</code></em> }; ]
   [ unix ...; ]
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="controls_statement_definition_and_usage"></a><span><strong class="command">controls</strong></span> Statement Definition and
          Usage</h3></div></div></div>
<p>
          The <span><strong class="command">controls</strong></span> statement declares control
          channels to be used by system administrators to control the
          operation of the name server. These control channels are
          used by the <span><strong class="command">rndc</strong></span> utility to send
          commands to and retrieve non-DNS results from a name server.
        </p>
<p>
          An <span><strong class="command">inet</strong></span> control channel is a TCP socket
          listening at the specified <span><strong class="command">ip_port</strong></span> on the
          specified <span><strong class="command">ip_addr</strong></span>, which can be an IPv4 or IPv6
          address.  An <span><strong class="command">ip_addr</strong></span> of <code class="literal">*</code> (asterisk) is
          interpreted as the IPv4 wildcard address; connections will be
          accepted on any of the system's IPv4 addresses.
          To listen on the IPv6 wildcard address,
          use an <span><strong class="command">ip_addr</strong></span> of <code class="literal">::</code>.
          If you will only use <span><strong class="command">rndc</strong></span> on the local host,
          using the loopback address (<code class="literal">127.0.0.1</code>
          or <code class="literal">::1</code>) is recommended for maximum security.
        </p>
<p>
          If no port is specified, port 953 is used. The asterisk
          "<code class="literal">*</code>" cannot be used for <span><strong class="command">ip_port</strong></span>.
        </p>
<p>
          The ability to issue commands over the control channel is
          restricted by the <span><strong class="command">allow</strong></span> and
          <span><strong class="command">keys</strong></span> clauses.
          Connections to the control channel are permitted based on the
          <span><strong class="command">address_match_list</strong></span>.  This is for simple
          IP address based filtering only; any <span><strong class="command">key_id</strong></span>
          elements of the <span><strong class="command">address_match_list</strong></span>
          are ignored.
        </p>
<p>
          A <span><strong class="command">unix</strong></span> control channel is a UNIX domain
          socket listening at the specified path in the file system.
          Access to the socket is specified by the <span><strong class="command">perm</strong></span>,
          <span><strong class="command">owner</strong></span> and <span><strong class="command">group</strong></span> clauses.
          Note on some platforms (SunOS and Solaris) the permissions
          (<span><strong class="command">perm</strong></span>) are applied to the parent directory
          as the permissions on the socket itself are ignored.
        </p>
<p>
          The primary authorization mechanism of the command
          channel is the <span><strong class="command">key_list</strong></span>, which
          contains a list of <span><strong class="command">key_id</strong></span>s.
          Each <span><strong class="command">key_id</strong></span> in the <span><strong class="command">key_list</strong></span>
          is authorized to execute commands over the control channel.
          See <a href="Bv9ARM.ch03.html#rndc">Remote Name Daemon Control application</a> in <a href="Bv9ARM.ch03.html#admin_tools" title="Administrative Tools">the section called &#8220;Administrative Tools&#8221;</a>)
          for information about configuring keys in <span><strong class="command">rndc</strong></span>.
        </p>
<p>
          If no <span><strong class="command">controls</strong></span> statement is present,
          <span><strong class="command">named</strong></span> will set up a default
          control channel listening on the loopback address 127.0.0.1
          and its IPv6 counterpart ::1.
          In this case, and also when the <span><strong class="command">controls</strong></span> statement
          is present but does not have a <span><strong class="command">keys</strong></span> clause,
          <span><strong class="command">named</strong></span> will attempt to load the command channel key
          from the file <code class="filename">rndc.key</code> in
          <code class="filename">/etc</code> (or whatever <code class="varname">sysconfdir</code>
          was specified as when <acronym class="acronym">BIND</acronym> was built).
          To create a <code class="filename">rndc.key</code> file, run
          <strong class="userinput"><code>rndc-confgen -a</code></strong>.
        </p>
<p>
          The <code class="filename">rndc.key</code> feature was created to
          ease the transition of systems from <acronym class="acronym">BIND</acronym> 8,
          which did not have digital signatures on its command channel
          messages and thus did not have a <span><strong class="command">keys</strong></span> clause.

          It makes it possible to use an existing <acronym class="acronym">BIND</acronym> 8
          configuration file in <acronym class="acronym">BIND</acronym> 9 unchanged,
          and still have <span><strong class="command">rndc</strong></span> work the same way
          <span><strong class="command">ndc</strong></span> worked in BIND 8, simply by executing the
          command <strong class="userinput"><code>rndc-confgen -a</code></strong> after BIND 9 is
          installed.
        </p>
<p>
          Since the <code class="filename">rndc.key</code> feature
          is only intended to allow the backward-compatible usage of
          <acronym class="acronym">BIND</acronym> 8 configuration files, this
          feature does not
          have a high degree of configurability.  You cannot easily change
          the key name or the size of the secret, so you should make a
          <code class="filename">rndc.conf</code> with your own key if you
          wish to change
          those things.  The <code class="filename">rndc.key</code> file
          also has its
          permissions set such that only the owner of the file (the user that
          <span><strong class="command">named</strong></span> is running as) can access it.
          If you
          desire greater flexibility in allowing other users to access
          <span><strong class="command">rndc</strong></span> commands, then you need to create
          a
          <code class="filename">rndc.conf</code> file and make it group
          readable by a group
          that contains the users who should have access.
        </p>
<p>
          To disable the command channel, use an empty
          <span><strong class="command">controls</strong></span> statement:
          <span><strong class="command">controls { };</strong></span>.
        </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574584"></a><span><strong class="command">include</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span><strong class="command">include</strong></span> <em class="replaceable"><code>filename</code></em>;</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574601"></a><span><strong class="command">include</strong></span> Statement Definition and
          Usage</h3></div></div></div>
<p>
          The <span><strong class="command">include</strong></span> statement inserts the
          specified file at the point where the <span><strong class="command">include</strong></span>
          statement is encountered. The <span><strong class="command">include</strong></span>
                statement facilitates the administration of configuration
          files
          by permitting the reading or writing of some things but not
          others. For example, the statement could include private keys
          that are readable only by the name server.
        </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574761"></a><span><strong class="command">key</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span><strong class="command">key</strong></span> <em class="replaceable"><code>key_id</code></em> {
    algorithm <em class="replaceable"><code>string</code></em>;
    secret <em class="replaceable"><code>string</code></em>;
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574785"></a><span><strong class="command">key</strong></span> Statement Definition and Usage</h3></div></div></div>
<p>
          The <span><strong class="command">key</strong></span> statement defines a shared
          secret key for use with TSIG (see <a href="Bv9ARM.ch04.html#tsig" title="TSIG">the section called &#8220;TSIG&#8221;</a>)
          or the command channel
          (see <a href="Bv9ARM.ch06.html#controls_statement_definition_and_usage" title="controls Statement Definition and
          Usage">the section called &#8220;<span><strong class="command">controls</strong></span> Statement Definition and
          Usage&#8221;</a>).
        </p>
<p>
          The <span><strong class="command">key</strong></span> statement can occur at the
          top level
          of the configuration file or inside a <span><strong class="command">view</strong></span>
          statement.  Keys defined in top-level <span><strong class="command">key</strong></span>
          statements can be used in all views.  Keys intended for use in
          a <span><strong class="command">controls</strong></span> statement
          (see <a href="Bv9ARM.ch06.html#controls_statement_definition_and_usage" title="controls Statement Definition and
          Usage">the section called &#8220;<span><strong class="command">controls</strong></span> Statement Definition and
          Usage&#8221;</a>)
          must be defined at the top level.
        </p>
<p>
          The <em class="replaceable"><code>key_id</code></em>, also known as the
          key name, is a domain name uniquely identifying the key. It can
          be used in a <span><strong class="command">server</strong></span>
          statement to cause requests sent to that
          server to be signed with this key, or in address match lists to
          verify that incoming requests have been signed with a key
          matching this name, algorithm, and secret.
        </p>
<p>
          The <em class="replaceable"><code>algorithm_id</code></em> is a string
          that specifies a security/authentication algorithm.  Named
          supports <code class="literal">hmac-md5</code>,
          <code class="literal">hmac-sha1</code>, <code class="literal">hmac-sha224</code>,
          <code class="literal">hmac-sha256</code>, <code class="literal">hmac-sha384</code>
          and <code class="literal">hmac-sha512</code> TSIG authentication.
          Truncated hashes are supported by appending the minimum
          number of required bits preceded by a dash, e.g.
          <code class="literal">hmac-sha1-80</code>.  The
          <em class="replaceable"><code>secret_string</code></em> is the secret
          to be used by the algorithm, and is treated as a base-64
          encoded string.
        </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574875"></a><span><strong class="command">logging</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span><strong class="command">logging</strong></span> {
   [ <span><strong class="command">channel</strong></span> <em class="replaceable"><code>channel_name</code></em> {
     ( <span><strong class="command">file</strong></span> <em class="replaceable"><code>path_name</code></em>
         [ <span><strong class="command">versions</strong></span> ( <em class="replaceable"><code>number</code></em> | <span><strong class="command">unlimited</strong></span> ) ]
         [ <span><strong class="command">size</strong></span> <em class="replaceable"><code>size_spec</code></em> ]
       | <span><strong class="command">syslog</strong></span> <em class="replaceable"><code>syslog_facility</code></em>
       | <span><strong class="command">stderr</strong></span>
       | <span><strong class="command">null</strong></span> );
     [ <span><strong class="command">severity</strong></span> (<code class="option">critical</code> | <code class="option">error</code> | <code class="option">warning</code> | <code class="option">notice</code> |
                 <code class="option">info</code> | <code class="option">debug</code> [ <em class="replaceable"><code>level</code></em> ] | <code class="option">dynamic</code> ); ]
     [ <span><strong class="command">print-category</strong></span> <code class="option">yes</code> or <code class="option">no</code>; ]
     [ <span><strong class="command">print-severity</strong></span> <code class="option">yes</code> or <code class="option">no</code>; ]
     [ <span><strong class="command">print-time</strong></span> <code class="option">yes</code> or <code class="option">no</code>; ]
   }; ]
   [ <span><strong class="command">category</strong></span> <em class="replaceable"><code>category_name</code></em> {
     <em class="replaceable"><code>channel_name</code></em> ; [ <em class="replaceable"><code>channel_name</code></em> ; ... ]
   }; ]
   ...
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2575001"></a><span><strong class="command">logging</strong></span> Statement Definition and
          Usage</h3></div></div></div>
<p>
          The <span><strong class="command">logging</strong></span> statement configures a
          wide
          variety of logging options for the name server. Its <span><strong class="command">channel</strong></span> phrase
          associates output methods, format options and severity levels with
          a name that can then be used with the <span><strong class="command">category</strong></span> phrase
          to select how various classes of messages are logged.
        </p>
<p>
          Only one <span><strong class="command">logging</strong></span> statement is used to
          define
          as many channels and categories as are wanted. If there is no <span><strong class="command">logging</strong></span> statement,
          the logging configuration will be:
        </p>
<pre class="programlisting">logging {
     category default { default_syslog; default_debug; };
     category unmatched { null; };
};
</pre>
<p>
          In <acronym class="acronym">BIND</acronym> 9, the logging configuration
          is only established when
          the entire configuration file has been parsed.  In <acronym class="acronym">BIND</acronym> 8, it was
          established as soon as the <span><strong class="command">logging</strong></span>
          statement
          was parsed. When the server is starting up, all logging messages
          regarding syntax errors in the configuration file go to the default
          channels, or to standard error if the "<code class="option">-g</code>" option
          was specified.
        </p>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2575053"></a>The <span><strong class="command">channel</strong></span> Phrase</h4></div></div></div>
<p>
            All log output goes to one or more <span class="emphasis"><em>channels</em></span>;
            you can make as many of them as you want.
          </p>
<p>
            Every channel definition must include a destination clause that
            says whether messages selected for the channel go to a file, to a
            particular syslog facility, to the standard error stream, or are
            discarded. It can optionally also limit the message severity level
            that will be accepted by the channel (the default is
            <span><strong class="command">info</strong></span>), and whether to include a
            <span><strong class="command">named</strong></span>-generated time stamp, the
            category name
            and/or severity level (the default is not to include any).
          </p>
<p>
            The <span><strong class="command">null</strong></span> destination clause
            causes all messages sent to the channel to be discarded;
            in that case, other options for the channel are meaningless.
          </p>
<p>
            The <span><strong class="command">file</strong></span> destination clause directs
            the channel
            to a disk file.  It can include limitations
            both on how large the file is allowed to become, and how many
            versions
            of the file will be saved each time the file is opened.
          </p>
<p>
            If you use the <span><strong class="command">versions</strong></span> log file
            option, then
            <span><strong class="command">named</strong></span> will retain that many backup
            versions of the file by
            renaming them when opening.  For example, if you choose to keep
            three old versions
            of the file <code class="filename">lamers.log</code>, then just
            before it is opened
            <code class="filename">lamers.log.1</code> is renamed to
            <code class="filename">lamers.log.2</code>, <code class="filename">lamers.log.0</code> is renamed
            to <code class="filename">lamers.log.1</code>, and <code class="filename">lamers.log</code> is
            renamed to <code class="filename">lamers.log.0</code>.
            You can say <span><strong class="command">versions unlimited</strong></span> to
            not limit
            the number of versions.
            If a <span><strong class="command">size</strong></span> option is associated with
            the log file,
            then renaming is only done when the file being opened exceeds the
            indicated size.  No backup versions are kept by default; any
            existing
            log file is simply appended.
          </p>
<p>
            The <span><strong class="command">size</strong></span> option for files is used
            to limit log
            growth. If the file ever exceeds the size, then <span><strong class="command">named</strong></span> will
            stop writing to the file unless it has a <span><strong class="command">versions</strong></span> option
            associated with it.  If backup versions are kept, the files are
            rolled as
            described above and a new one begun.  If there is no
            <span><strong class="command">versions</strong></span> option, no more data will
            be written to the log
            until some out-of-band mechanism removes or truncates the log to
            less than the
            maximum size.  The default behavior is not to limit the size of
            the
            file.
          </p>
<p>
            Example usage of the <span><strong class="command">size</strong></span> and
            <span><strong class="command">versions</strong></span> options:
          </p>
<pre class="programlisting">channel an_example_channel {
    file "example.log" versions 3 size 20m;
    print-time yes;
    print-category yes;
};
</pre>
<p>
            The <span><strong class="command">syslog</strong></span> destination clause
            directs the
            channel to the system log.  Its argument is a
            syslog facility as described in the <span><strong class="command">syslog</strong></span> man
            page. Known facilities are <span><strong class="command">kern</strong></span>, <span><strong class="command">user</strong></span>,
            <span><strong class="command">mail</strong></span>, <span><strong class="command">daemon</strong></span>, <span><strong class="command">auth</strong></span>,
            <span><strong class="command">syslog</strong></span>, <span><strong class="command">lpr</strong></span>, <span><strong class="command">news</strong></span>,
            <span><strong class="command">uucp</strong></span>, <span><strong class="command">cron</strong></span>, <span><strong class="command">authpriv</strong></span>,
            <span><strong class="command">ftp</strong></span>, <span><strong class="command">local0</strong></span>, <span><strong class="command">local1</strong></span>,
            <span><strong class="command">local2</strong></span>, <span><strong class="command">local3</strong></span>, <span><strong class="command">local4</strong></span>,
            <span><strong class="command">local5</strong></span>, <span><strong class="command">local6</strong></span> and
            <span><strong class="command">local7</strong></span>, however not all facilities
            are supported on
            all operating systems.
            How <span><strong class="command">syslog</strong></span> will handle messages
            sent to
            this facility is described in the <span><strong class="command">syslog.conf</strong></span> man
            page. If you have a system which uses a very old version of <span><strong class="command">syslog</strong></span> that
            only uses two arguments to the <span><strong class="command">openlog()</strong></span> function,
            then this clause is silently ignored.
          </p>
<p>
            On Windows machines syslog messages are directed to the EventViewer.
          </p>
<p>
            The <span><strong class="command">severity</strong></span> clause works like <span><strong class="command">syslog</strong></span>'s
            "priorities", except that they can also be used if you are writing
            straight to a file rather than using <span><strong class="command">syslog</strong></span>.
            Messages which are not at least of the severity level given will
            not be selected for the channel; messages of higher severity
            levels
            will be accepted.
          </p>
<p>
            If you are using <span><strong class="command">syslog</strong></span>, then the <span><strong class="command">syslog.conf</strong></span> priorities
            will also determine what eventually passes through. For example,
            defining a channel facility and severity as <span><strong class="command">daemon</strong></span> and <span><strong class="command">debug</strong></span> but
            only logging <span><strong class="command">daemon.warning</strong></span> via <span><strong class="command">syslog.conf</strong></span> will
            cause messages of severity <span><strong class="command">info</strong></span> and
            <span><strong class="command">notice</strong></span> to
            be dropped. If the situation were reversed, with <span><strong class="command">named</strong></span> writing
            messages of only <span><strong class="command">warning</strong></span> or higher,
            then <span><strong class="command">syslogd</strong></span> would
            print all messages it received from the channel.
          </p>
<p>
            The <span><strong class="command">stderr</strong></span> destination clause
            directs the
            channel to the server's standard error stream.  This is intended
            for
            use when the server is running as a foreground process, for
            example
            when debugging a configuration.
          </p>
<p>
            The server can supply extensive debugging information when
            it is in debugging mode. If the server's global debug level is
            greater
            than zero, then debugging mode will be active. The global debug
            level is set either by starting the <span><strong class="command">named</strong></span> server
            with the <code class="option">-d</code> flag followed by a positive integer,
            or by running <span><strong class="command">rndc trace</strong></span>.
            The global debug level
            can be set to zero, and debugging mode turned off, by running <span><strong class="command">rndc
notrace</strong></span>. All debugging messages in the server have a debug
            level, and higher debug levels give more detailed output. Channels
            that specify a specific debug severity, for example:
          </p>
<pre class="programlisting">channel specific_debug_level {
    file "foo";
    severity debug 3;
};
</pre>
<p>
            will get debugging output of level 3 or less any time the
            server is in debugging mode, regardless of the global debugging
            level. Channels with <span><strong class="command">dynamic</strong></span>
            severity use the
            server's global debug level to determine what messages to print.
          </p>
<p>
            If <span><strong class="command">print-time</strong></span> has been turned on,
            then
            the date and time will be logged. <span><strong class="command">print-time</strong></span> may
            be specified for a <span><strong class="command">syslog</strong></span> channel,
            but is usually
            pointless since <span><strong class="command">syslog</strong></span> also logs
            the date and
            time. If <span><strong class="command">print-category</strong></span> is
            requested, then the
            category of the message will be logged as well. Finally, if <span><strong class="command">print-severity</strong></span> is
            on, then the severity level of the message will be logged. The <span><strong class="command">print-</strong></span> options may
            be used in any combination, and will always be printed in the
            following
            order: time, category, severity. Here is an example where all
            three <span><strong class="command">print-</strong></span> options
            are on:
          </p>
<p>
            <code class="computeroutput">28-Feb-2000 15:05:32.863 general: notice: running</code>
          </p>
<p>
            There are four predefined channels that are used for
            <span><strong class="command">named</strong></span>'s default logging as follows.
            How they are
            used is described in <a href="Bv9ARM.ch06.html#the_category_phrase" title="The category Phrase">the section called &#8220;The <span><strong class="command">category</strong></span> Phrase&#8221;</a>.
          </p>
<pre class="programlisting">channel default_syslog {
    // send to syslog's daemon facility
    syslog daemon;
    // only send priority info and higher
    severity info;

channel default_debug {
    // write to named.run in the working directory
    // Note: stderr is used instead of "named.run" if
    // the server is started with the '-f' option.
    file "named.run";
    // log at the server's current debug level
    severity dynamic;
};

channel default_stderr {
    // writes to stderr
    stderr;
    // only send priority info and higher
    severity info;
};

channel null {
   // toss anything sent to this channel
   null;
};
</pre>
<p>
            The <span><strong class="command">default_debug</strong></span> channel has the
            special
            property that it only produces output when the server's debug
            level is
            nonzero.  It normally writes to a file called <code class="filename">named.run</code>
            in the server's working directory.
          </p>
<p>
            For security reasons, when the "<code class="option">-u</code>"
            command line option is used, the <code class="filename">named.run</code> file
            is created only after <span><strong class="command">named</strong></span> has
            changed to the
            new UID, and any debug output generated while <span><strong class="command">named</strong></span> is
            starting up and still running as root is discarded.  If you need
            to capture this output, you must run the server with the "<code class="option">-g</code>"
            option and redirect standard error to a file.
          </p>
<p>
            Once a channel is defined, it cannot be redefined. Thus you
            cannot alter the built-in channels directly, but you can modify
            the default logging by pointing categories at channels you have
            defined.
          </p>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="the_category_phrase"></a>The <span><strong class="command">category</strong></span> Phrase</h4></div></div></div>
<p>
            There are many categories, so you can send the logs you want
            to see wherever you want, without seeing logs you don't want. If
            you don't specify a list of channels for a category, then log
            messages
            in that category will be sent to the <span><strong class="command">default</strong></span> category
            instead. If you don't specify a default category, the following
            "default default" is used:
          </p>
<pre class="programlisting">category default { default_syslog; default_debug; };
</pre>
<p>
            As an example, let's say you want to log security events to
            a file, but you also want keep the default logging behavior. You'd
            specify the following:
          </p>
<pre class="programlisting">channel my_security_channel {
    file "my_security_file";
    severity info;
};
category security {
    my_security_channel;
    default_syslog;
    default_debug;
};</pre>
<p>
            To discard all messages in a category, specify the <span><strong class="command">null</strong></span> channel:
          </p>
<pre class="programlisting">category xfer-out { null; };
category notify { null; };
</pre>
<p>
            Following are the available categories and brief descriptions
            of the types of log information they contain. More
            categories may be added in future <acronym class="acronym">BIND</acronym> releases.
          </p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                    <p><span><strong class="command">default</strong></span></p>
                  </td>
<td>
                    <p>
                      The default category defines the logging
                      options for those categories where no specific
                      configuration has been
                      defined.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">general</strong></span></p>
                  </td>
<td>
                    <p>
                      The catch-all. Many things still aren't
                      classified into categories, and they all end up here.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">database</strong></span></p>
                  </td>
<td>
                    <p>
                      Messages relating to the databases used
                      internally by the name server to store zone and cache
                      data.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">security</strong></span></p>
                  </td>
<td>
                    <p>
                      Approval and denial of requests.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">config</strong></span></p>
                  </td>
<td>
                    <p>
                      Configuration file parsing and processing.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">resolver</strong></span></p>
                  </td>
<td>
                    <p>
                      DNS resolution, such as the recursive
                      lookups performed on behalf of clients by a caching name
                      server.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">xfer-in</strong></span></p>
                  </td>
<td>
                    <p>
                      Zone transfers the server is receiving.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">xfer-out</strong></span></p>
                  </td>
<td>
                    <p>
                      Zone transfers the server is sending.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">notify</strong></span></p>
                  </td>
<td>
                    <p>
                      The NOTIFY protocol.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">client</strong></span></p>
                  </td>
<td>
                    <p>
                      Processing of client requests.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">unmatched</strong></span></p>
                  </td>
<td>
                    <p>
                      Messages that <span><strong class="command">named</strong></span> was unable to determine the
                      class of or for which there was no matching <span><strong class="command">view</strong></span>.
                      A one line summary is also logged to the <span><strong class="command">client</strong></span> category.
                      This category is best sent to a file or stderr, by
                      default it is sent to
                      the <span><strong class="command">null</strong></span> channel.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">network</strong></span></p>
                  </td>
<td>
                    <p>
                      Network operations.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">update</strong></span></p>
                  </td>
<td>
                    <p>
                      Dynamic updates.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">update-security</strong></span></p>
                  </td>
<td>
                    <p>
                      Approval and denial of update requests.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">queries</strong></span></p>
                  </td>
<td>
                    <p>
                      Specify where queries should be logged to.
                    </p>
                    <p>
                      At startup, specifying the category <span><strong class="command">queries</strong></span> will also
                      enable query logging unless <span><strong class="command">querylog</strong></span> option has been
                      specified.
                    </p>

                    <p>
                      The query log entry reports the client's IP
                      address and port number, and the query name,
                      class and type.  Next it reports whether the
                      Recursion Desired flag was set (+ if set, -
                      if not set), if the query was signed (S),
                      EDNS was in use (E), if TCP was used (T), if
                      DO (DNSSEC Ok) was set (D), or if CD (Checking
                      Disabled) was set (C).  After this the
                      destination address the query was sent to is
                      reported.
                    </p>

                    <p>
                      <code class="computeroutput">client 127.0.0.1#62536 (www.example.com): query: www.example.com IN AAAA +SE</code>
                    </p>
                    <p>
                      <code class="computeroutput">client ::1#62537 (www.example.net): query: www.example.net IN AAAA -SE</code>
                    </p>
                    <p>
                      (The first part of this log message, showing the
                      client address/port number and query name, is
                      repeated in all subsequent log messages related
                      to the same query.)
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">query-errors</strong></span></p>
                  </td>
<td>
                    <p>
                      Information about queries that resulted in some
                      failure.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">dispatch</strong></span></p>
                  </td>
<td>
                    <p>
                      Dispatching of incoming packets to the
                      server modules where they are to be processed.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">dnssec</strong></span></p>
                  </td>
<td>
                    <p>
                      DNSSEC and TSIG protocol processing.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">lame-servers</strong></span></p>
                  </td>
<td>
                    <p>
                      Lame servers.  These are misconfigurations
                      in remote servers, discovered by BIND 9 when trying to
                      query those servers during resolution.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">delegation-only</strong></span></p>
                  </td>
<td>
                    <p>
                      Delegation only.  Logs queries that have been
                      forced to NXDOMAIN as the result of a
                      delegation-only zone or a
                      <span><strong class="command">delegation-only</strong></span> in a
                      forward, hint or stub zone declaration.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">edns-disabled</strong></span></p>
                  </td>
<td>
                    <p>
                      Log queries that have been forced to use plain
                      DNS due to timeouts.  This is often due to
                      the remote servers not being RFC 1034 compliant
                      (not always returning FORMERR or similar to
                      EDNS queries and other extensions to the DNS
                      when they are not understood).  In other words, this is
                      targeted at servers that fail to respond to
                      DNS queries that they don't understand.
                    </p>
                    <p>
                      Note: the log message can also be due to
                      packet loss.  Before reporting servers for
                      non-RFC 1034 compliance they should be re-tested
                      to determine the nature of the non-compliance.
                      This testing should prevent or reduce the
                      number of false-positive reports.
                    </p>
                    <p>
                      Note: eventually <span><strong class="command">named</strong></span> will have to stop
                      treating such timeouts as due to RFC 1034 non
                      compliance and start treating it as plain
                      packet loss.  Falsely classifying packet
                      loss as due to RFC 1034 non compliance impacts
                      on DNSSEC validation which requires EDNS for
                      the DNSSEC records to be returned.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">RPZ</strong></span></p>
                  </td>
<td>
                    <p>
                      Information about errors in response policy zone files,
                      rewritten responses, and at the highest
                      <span><strong class="command">debug</strong></span> levels, mere rewriting
                      attempts.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">rate-limit</strong></span></p>
                  </td>
<td>
                    <p>
                      (Only available when <acronym class="acronym">BIND</acronym> 9 is
                      configured with the <strong class="userinput"><code>--enable-rrl</code></strong>
                      option at compile time.)
                    </p>
                    <p>
                      The start, periodic, and final notices of the
                      rate limiting of a stream of responses are logged at
                      <span><strong class="command">info</strong></span> severity in this category.
                      These messages include a hash value of the domain name
                      of the response and the name itself,
                      except when there is insufficient memory to record
                      the name for the final notice
                      The final notice is normally delayed until about one
                      minute after rate limit stops.
                      A lack of memory can hurry the final notice,
                      in which case it starts with an asterisk (*).
                      Various internal events are logged at debug 1 level
                      and higher.
                    </p>
                    <p>
                      Rate limiting of individual requests
                      is logged in the <span><strong class="command">query-errors</strong></span> category.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">cname</strong></span></p>
                  </td>
<td>
                    <p>
                      Logs nameservers that are skipped due to them being
                      a CNAME rather than A / AAAA records.
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2576580"></a>The <span><strong class="command">query-errors</strong></span> Category</h4></div></div></div>
<p>
            The <span><strong class="command">query-errors</strong></span> category is
            specifically intended for debugging purposes: To identify
            why and how specific queries result in responses which
            indicate an error.
            Messages of this category are therefore only logged
            with <span><strong class="command">debug</strong></span> levels.
          </p>
<p>
            At the debug levels of 1 or higher, each response with the
            rcode of SERVFAIL is logged as follows:
          </p>
<p>
            <code class="computeroutput">client 127.0.0.1#61502: query failed (SERVFAIL) for www.example.com/IN/AAAA at query.c:3880</code>
          </p>
<p>
            This means an error resulting in SERVFAIL was
            detected at line 3880 of source file
            <code class="filename">query.c</code>.
            Log messages of this level will particularly
            help identify the cause of SERVFAIL for an
            authoritative server.
          </p>
<p>
            At the debug levels of 2 or higher, detailed context
            information of recursive resolutions that resulted in
            SERVFAIL is logged.
            The log message will look like as follows:
          </p>
<p>

            </p>
<pre class="programlisting">
fetch completed at resolver.c:2970 for www.example.com/A
in 30.000183: timed out/success [domain:example.com,
referral:2,restart:7,qrysent:8,timeout:5,lame:0,neterr:0,
badresp:1,adberr:0,findfail:0,valfail:0]
            </pre>
<p>
          </p>
<p>
            The first part before the colon shows that a recursive
            resolution for AAAA records of www.example.com completed
            in 30.000183 seconds and the final result that led to the
            SERVFAIL was determined at line 2970 of source file
            <code class="filename">resolver.c</code>.
          </p>
<p>
            The following part shows the detected final result and the
            latest result of DNSSEC validation.
            The latter is always success when no validation attempt
            is made.
            In this example, this query resulted in SERVFAIL probably
            because all name servers are down or unreachable, leading
            to a timeout in 30 seconds.
            DNSSEC validation was probably not attempted.
          </p>
<p>
            The last part enclosed in square brackets shows statistics
            information collected for this particular resolution
            attempt.
            The <code class="varname">domain</code> field shows the deepest zone
            that the resolver reached;
            it is the zone where the error was finally detected.
            The meaning of the other fields is summarized in the
            following table.
          </p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                    <p><code class="varname">referral</code></p>
                  </td>
<td>
                    <p>
                      The number of referrals the resolver received
                      throughout the resolution process.
                      In the above example this is 2, which are most
                      likely com and example.com.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><code class="varname">restart</code></p>
                  </td>
<td>
                    <p>
                      The number of cycles that the resolver tried
                      remote servers at the <code class="varname">domain</code>
                      zone.
                      In each cycle the resolver sends one query
                      (possibly resending it, depending on the response)
                      to each known name server of
                      the <code class="varname">domain</code> zone.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><code class="varname">qrysent</code></p>
                  </td>
<td>
                    <p>
                      The number of queries the resolver sent at the
                      <code class="varname">domain</code> zone.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><code class="varname">timeout</code></p>
                  </td>
<td>
                    <p>
                      The number of timeouts since the resolver
                      received the last response.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><code class="varname">lame</code></p>
                  </td>
<td>
                    <p>
                      The number of lame servers the resolver detected
                      at the <code class="varname">domain</code> zone.
                      A server is detected to be lame either by an
                      invalid response or as a result of lookup in
                      BIND9's address database (ADB), where lame
                      servers are cached.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><code class="varname">neterr</code></p>
                  </td>
<td>
                    <p>
                      The number of erroneous results that the
                      resolver encountered in sending queries
                      at the <code class="varname">domain</code> zone.
                      One common case is the remote server is
                      unreachable and the resolver receives an ICMP
                      unreachable error message.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><code class="varname">badresp</code></p>
                  </td>
<td>
                    <p>
                      The number of unexpected responses (other than
                      <code class="varname">lame</code>) to queries sent by the
                      resolver at the <code class="varname">domain</code> zone.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><code class="varname">adberr</code></p>
                  </td>
<td>
                    <p>
                      Failures in finding remote server addresses
                      of the <code class="varname">domain</code> zone in the ADB.
                      One common case of this is that the remote
                      server's name does not have any address records.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><code class="varname">findfail</code></p>
                  </td>
<td>
                    <p>
                      Failures of resolving remote server addresses.
                      This is a total number of failures throughout
                      the resolution process.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><code class="varname">valfail</code></p>
                  </td>
<td>
                    <p>
                      Failures of DNSSEC validation.
                      Validation failures are counted throughout
                      the resolution process (not limited to
                      the <code class="varname">domain</code> zone), but should
                      only happen in <code class="varname">domain</code>.
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<p>
            At the debug levels of 3 or higher, the same messages
            as those at the debug 1 level are logged for other errors
            than SERVFAIL.
            Note that negative responses such as NXDOMAIN are not
            regarded as errors here.
          </p>
<p>
            At the debug levels of 4 or higher, the same messages
            as those at the debug 2 level are logged for other errors
            than SERVFAIL.
            Unlike the above case of level 3, messages are logged for
            negative responses.
            This is because any unexpected results can be difficult to
            debug in the recursion case.
          </p>
</div>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2577168"></a><span><strong class="command">lwres</strong></span> Statement Grammar</h3></div></div></div>
<p>
           This is the grammar of the <span><strong class="command">lwres</strong></span>
          statement in the <code class="filename">named.conf</code> file:
        </p>
<pre class="programlisting"><span><strong class="command">lwres</strong></span> {
    [<span class="optional"> listen-on { <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ;
                [<span class="optional"> <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; ... </span>] }; </span>]
    [<span class="optional"> view <em class="replaceable"><code>view_name</code></em>; </span>]
    [<span class="optional"> search { <em class="replaceable"><code>domain_name</code></em> ; [<span class="optional"> <em class="replaceable"><code>domain_name</code></em> ; ... </span>] }; </span>]
    [<span class="optional"> ndots <em class="replaceable"><code>number</code></em>; </span>]
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2577241"></a><span><strong class="command">lwres</strong></span> Statement Definition and Usage</h3></div></div></div>
<p>
          The <span><strong class="command">lwres</strong></span> statement configures the
          name
          server to also act as a lightweight resolver server. (See
          <a href="Bv9ARM.ch05.html#lwresd" title="Running a Resolver Daemon">the section called &#8220;Running a Resolver Daemon&#8221;</a>.)  There may be multiple
          <span><strong class="command">lwres</strong></span> statements configuring
          lightweight resolver servers with different properties.
        </p>
<p>
          The <span><strong class="command">listen-on</strong></span> statement specifies a
          list of
          IPv4 addresses (and ports) that this instance of a lightweight
          resolver daemon
          should accept requests on.  If no port is specified, port 921 is
          used.
          If this statement is omitted, requests will be accepted on
          127.0.0.1,
          port 921.
        </p>
<p>
          The <span><strong class="command">view</strong></span> statement binds this
          instance of a
          lightweight resolver daemon to a view in the DNS namespace, so that
          the
          response will be constructed in the same manner as a normal DNS
          query
          matching this view.  If this statement is omitted, the default view
          is
          used, and if there is no default view, an error is triggered.
        </p>
<p>
          The <span><strong class="command">search</strong></span> statement is equivalent to
          the
          <span><strong class="command">search</strong></span> statement in
          <code class="filename">/etc/resolv.conf</code>.  It provides a
          list of domains
          which are appended to relative names in queries.
        </p>
<p>
          The <span><strong class="command">ndots</strong></span> statement is equivalent to
          the
          <span><strong class="command">ndots</strong></span> statement in
          <code class="filename">/etc/resolv.conf</code>.  It indicates the
          minimum
          number of dots in a relative domain name that should result in an
          exact match lookup before search path elements are appended.
        </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2577305"></a><span><strong class="command">masters</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting">
<span><strong class="command">masters</strong></span> <em class="replaceable"><code>name</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] { ( <em class="replaceable"><code>masters_list</code></em> | 
      <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] [<span class="optional">key <em class="replaceable"><code>key</code></em></span>] ) ; [<span class="optional">...</span>] };
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2577417"></a><span><strong class="command">masters</strong></span> Statement Definition and
          Usage</h3></div></div></div>
<p><span><strong class="command">masters</strong></span>
          lists allow for a common set of masters to be easily used by
          multiple stub and slave zones in their <span><strong class="command">masters</strong></span>
          or <span><strong class="command">also-notify</strong></span> lists.
        </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2577438"></a><span><strong class="command">options</strong></span> Statement Grammar</h3></div></div></div>
<p>
          This is the grammar of the <span><strong class="command">options</strong></span>
          statement in the <code class="filename">named.conf</code> file:
        </p>
<pre class="programlisting"><span><strong class="command">options</strong></span> {
    [<span class="optional"> attach-cache <em class="replaceable"><code>cache_name</code></em>; </span>]
    [<span class="optional"> version <em class="replaceable"><code>version_string</code></em>; </span>]
    [<span class="optional"> hostname <em class="replaceable"><code>hostname_string</code></em>; </span>]
    [<span class="optional"> server-id <em class="replaceable"><code>server_id_string</code></em>; </span>]
    [<span class="optional"> directory <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> key-directory <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> managed-keys-directory <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> named-xfer <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> tkey-gssapi-keytab <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> tkey-gssapi-credential <em class="replaceable"><code>principal</code></em>; </span>]
    [<span class="optional"> tkey-domain <em class="replaceable"><code>domainname</code></em>; </span>]
    [<span class="optional"> tkey-dhkey <em class="replaceable"><code>key_name</code></em> <em class="replaceable"><code>key_tag</code></em>; </span>]
    [<span class="optional"> cache-file <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> dump-file <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> bindkeys-file <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> secroots-file <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> session-keyfile <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> session-keyname <em class="replaceable"><code>key_name</code></em>; </span>]
    [<span class="optional"> session-keyalg <em class="replaceable"><code>algorithm_id</code></em>; </span>]
    [<span class="optional"> memstatistics <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> memstatistics-file <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> pid-file <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> recursing-file <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> statistics-file <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> zone-statistics <em class="replaceable"><code>full</code></em> | <em class="replaceable"><code>terse</code></em> | <em class="replaceable"><code>none</code></em>; </span>]
    [<span class="optional"> auth-nxdomain <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> deallocate-on-exit <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> dialup <em class="replaceable"><code>dialup_option</code></em>; </span>]
    [<span class="optional"> fake-iquery <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> fetch-glue <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> flush-zones-on-shutdown <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> has-old-clients <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> host-statistics <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> host-statistics-max <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> minimal-responses <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> multiple-cnames <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> notify <em class="replaceable"><code>yes_or_no</code></em> | <em class="replaceable"><code>explicit</code></em> | <em class="replaceable"><code>master-only</code></em>; </span>]
    [<span class="optional"> recursion <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> request-nsid <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> rfc2308-type1 <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> use-id-pool <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> maintain-ixfr-base <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> ixfr-from-differences (<em class="replaceable"><code>yes_or_no</code></em> | <code class="constant">master</code> | <code class="constant">slave</code>); </span>]
    [<span class="optional"> dnssec-enable <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> dnssec-validation (<em class="replaceable"><code>yes_or_no</code></em> | <code class="constant">auto</code>); </span>]
    [<span class="optional"> dnssec-lookaside ( <em class="replaceable"><code>auto</code></em> |
                        <em class="replaceable"><code>no</code></em> |
                        <em class="replaceable"><code>domain</code></em> trust-anchor <em class="replaceable"><code>domain</code></em> ); </span>]
    [<span class="optional"> dnssec-must-be-secure <em class="replaceable"><code>domain yes_or_no</code></em>; </span>]
    [<span class="optional"> dnssec-accept-expired <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> forward ( <em class="replaceable"><code>only</code></em> | <em class="replaceable"><code>first</code></em> ); </span>]
    [<span class="optional"> forwarders { [<span class="optional"> <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; ... </span>] }; </span>]
    [<span class="optional"> dual-stack-servers [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] {
        ( <em class="replaceable"><code>domain_name</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] |
          <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ) ; 
        ... }; </span>]
    [<span class="optional"> check-names ( <em class="replaceable"><code>master</code></em> | <em class="replaceable"><code>slave</code></em> | <em class="replaceable"><code>response</code></em> )
        ( <em class="replaceable"><code>warn</code></em> | <em class="replaceable"><code>fail</code></em> | <em class="replaceable"><code>ignore</code></em> ); </span>]
    [<span class="optional"> check-dup-records ( <em class="replaceable"><code>warn</code></em> | <em class="replaceable"><code>fail</code></em> | <em class="replaceable"><code>ignore</code></em> ); </span>]
    [<span class="optional"> check-mx ( <em class="replaceable"><code>warn</code></em> | <em class="replaceable"><code>fail</code></em> | <em class="replaceable"><code>ignore</code></em> ); </span>]
    [<span class="optional"> check-wildcard <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> check-integrity <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> check-mx-cname ( <em class="replaceable"><code>warn</code></em> | <em class="replaceable"><code>fail</code></em> | <em class="replaceable"><code>ignore</code></em> ); </span>]
    [<span class="optional"> check-srv-cname ( <em class="replaceable"><code>warn</code></em> | <em class="replaceable"><code>fail</code></em> | <em class="replaceable"><code>ignore</code></em> ); </span>]
    [<span class="optional"> check-sibling <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> check-spf ( <em class="replaceable"><code>warn</code></em> | <em class="replaceable"><code>ignore</code></em> ); </span>]
    [<span class="optional"> allow-new-zones { <em class="replaceable"><code>yes_or_no</code></em> }; </span>]
    [<span class="optional"> allow-notify { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-query { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-query-on { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-query-cache { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-query-cache-on { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-transfer { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-recursion { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-recursion-on { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-update { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-update-forwarding { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> update-check-ksk <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> dnssec-update-mode ( <em class="replaceable"><code>maintain</code></em> | <em class="replaceable"><code>no-resign</code></em> ); </span>]
    [<span class="optional"> dnssec-dnskey-kskonly <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> dnssec-loadkeys-interval <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> dnssec-secure-to-insecure <em class="replaceable"><code>yes_or_no</code></em> ;</span>]
    [<span class="optional"> try-tcp-refresh <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> allow-v6-synthesis { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> blackhole { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> no-case-compress { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> use-v4-udp-ports { <em class="replaceable"><code>port_list</code></em> }; </span>]
    [<span class="optional"> avoid-v4-udp-ports { <em class="replaceable"><code>port_list</code></em> }; </span>]
    [<span class="optional"> use-v6-udp-ports { <em class="replaceable"><code>port_list</code></em> }; </span>]
    [<span class="optional"> avoid-v6-udp-ports { <em class="replaceable"><code>port_list</code></em> }; </span>]
    [<span class="optional"> listen-on [<span class="optional"> port <em class="replaceable"><code>ip_port</code></em> </span>] { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> listen-on-v6 [<span class="optional"> port <em class="replaceable"><code>ip_port</code></em> </span>] { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> query-source ( ( <em class="replaceable"><code>ip4_addr</code></em> | <em class="replaceable"><code>*</code></em> )
        [<span class="optional"> port ( <em class="replaceable"><code>ip_port</code></em> | <em class="replaceable"><code>*</code></em> ) </span>] |
        [<span class="optional"> address ( <em class="replaceable"><code>ip4_addr</code></em> | <em class="replaceable"><code>*</code></em> ) </span>]
        [<span class="optional"> port ( <em class="replaceable"><code>ip_port</code></em> | <em class="replaceable"><code>*</code></em> ) </span>] ) ; </span>]
    [<span class="optional"> query-source-v6 ( ( <em class="replaceable"><code>ip6_addr</code></em> | <em class="replaceable"><code>*</code></em> )
        [<span class="optional"> port ( <em class="replaceable"><code>ip_port</code></em> | <em class="replaceable"><code>*</code></em> ) </span>] | 
        [<span class="optional"> address ( <em class="replaceable"><code>ip6_addr</code></em> | <em class="replaceable"><code>*</code></em> ) </span>] 
        [<span class="optional"> port ( <em class="replaceable"><code>ip_port</code></em> | <em class="replaceable"><code>*</code></em> ) </span>] ) ; </span>]
    [<span class="optional"> use-queryport-pool <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> queryport-pool-ports <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> queryport-pool-updateinterval <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> max-transfer-time-in <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> max-transfer-time-out <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> max-transfer-idle-in <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> max-transfer-idle-out <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> tcp-clients <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> reserved-sockets <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> recursive-clients <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> serial-query-rate <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> serial-queries <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> tcp-listen-queue <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> transfer-format <em class="replaceable"><code>( one-answer | many-answers )</code></em>; </span>]
    [<span class="optional"> transfers-in  <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> transfers-out <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> transfers-per-ns <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> transfer-source (<em class="replaceable"><code>ip4_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> transfer-source-v6 (<em class="replaceable"><code>ip6_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> alt-transfer-source (<em class="replaceable"><code>ip4_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> alt-transfer-source-v6 (<em class="replaceable"><code>ip6_addr</code></em> | <code class="constant">*</code>)
                             [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> use-alt-transfer-source <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> notify-delay <em class="replaceable"><code>seconds</code></em> ; </span>]
    [<span class="optional"> notify-source (<em class="replaceable"><code>ip4_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> notify-source-v6 (<em class="replaceable"><code>ip6_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> notify-to-soa <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> also-notify { <em class="replaceable"><code>ip_addr</code></em>
                    [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] [<span class="optional">key <em class="replaceable"><code>keyname</code></em></span>] ;
                    [<span class="optional"> <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] [<span class="optional">key <em class="replaceable"><code>keyname</code></em></span>] ; ... </span>] }; </span>]
    [<span class="optional"> max-ixfr-log-size <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> max-journal-size <em class="replaceable"><code>size_spec</code></em>; </span>]
    [<span class="optional"> coresize <em class="replaceable"><code>size_spec</code></em> ; </span>]
    [<span class="optional"> datasize <em class="replaceable"><code>size_spec</code></em> ; </span>]
    [<span class="optional"> files <em class="replaceable"><code>size_spec</code></em> ; </span>]
    [<span class="optional"> stacksize <em class="replaceable"><code>size_spec</code></em> ; </span>]
    [<span class="optional"> cleaning-interval <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> heartbeat-interval <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> interface-interval <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> statistics-interval <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> topology { <em class="replaceable"><code>address_match_list</code></em> }</span>];
    [<span class="optional"> sortlist { <em class="replaceable"><code>address_match_list</code></em> }</span>];
    [<span class="optional"> rrset-order { <em class="replaceable"><code>order_spec</code></em> ; [<span class="optional"> <em class="replaceable"><code>order_spec</code></em> ; ... </span>] </span>] };
    [<span class="optional"> lame-ttl <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> max-ncache-ttl <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> max-cache-ttl <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> sig-validity-interval <em class="replaceable"><code>number</code></em> [<span class="optional"><em class="replaceable"><code>number</code></em></span>] ; </span>]
    [<span class="optional"> sig-signing-nodes <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> sig-signing-signatures <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> sig-signing-type <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> min-roots <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> use-ixfr <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> provide-ixfr <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> request-ixfr <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> treat-cr-as-space <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> min-refresh-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-refresh-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> min-retry-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-retry-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> port <em class="replaceable"><code>ip_port</code></em>; </span>]
    [<span class="optional"> additional-from-auth <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> additional-from-cache <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> random-device <em class="replaceable"><code>path_name</code></em> ; </span>]
    [<span class="optional"> max-cache-size <em class="replaceable"><code>size_spec</code></em> ; </span>]
    [<span class="optional"> match-mapped-addresses <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> filter-aaaa-on-v4 ( <em class="replaceable"><code>yes_or_no</code></em> | <em class="replaceable"><code>break-dnssec</code></em> ); </span>]
    [<span class="optional"> filter-aaaa { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> dns64 <em class="replaceable"><code>ipv6-prefix</code></em> {
        [<span class="optional"> clients { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
        [<span class="optional"> mapped { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
        [<span class="optional"> exclude { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
        [<span class="optional"> suffix IPv6-address; </span>]
        [<span class="optional"> recursive-only <em class="replaceable"><code>yes_or_no</code></em>; </span>]
        [<span class="optional"> break-dnssec <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    }; </span>];
    [<span class="optional"> dns64-server <em class="replaceable"><code>name</code></em> </span>]
    [<span class="optional"> dns64-contact <em class="replaceable"><code>name</code></em> </span>]
    [<span class="optional"> preferred-glue ( <em class="replaceable"><code>A</code></em> | <em class="replaceable"><code>AAAA</code></em> | <em class="replaceable"><code>NONE</code></em> ); </span>]
    [<span class="optional"> edns-udp-size <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> max-udp-size <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> max-rsa-exponent-size <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> root-delegation-only [<span class="optional"> exclude { <em class="replaceable"><code>namelist</code></em> } </span>] ; </span>]
    [<span class="optional"> querylog <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> disable-algorithms <em class="replaceable"><code>domain</code></em> { <em class="replaceable"><code>algorithm</code></em>;
                                [<span class="optional"> <em class="replaceable"><code>algorithm</code></em>; </span>] }; </span>]
    [<span class="optional"> acache-enable <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> acache-cleaning-interval <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> max-acache-size <em class="replaceable"><code>size_spec</code></em> ; </span>]
    [<span class="optional"> clients-per-query <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-clients-per-query <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-recursion-depth <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-recursion-queries <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> masterfile-format (<code class="constant">text</code>|<code class="constant">raw</code>) ; </span>]
    [<span class="optional"> empty-server <em class="replaceable"><code>name</code></em> ; </span>]
    [<span class="optional"> empty-contact <em class="replaceable"><code>name</code></em> ; </span>]
    [<span class="optional"> empty-zones-enable <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> disable-empty-zone <em class="replaceable"><code>zone_name</code></em> ; </span>]
    [<span class="optional"> zero-no-soa-ttl <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> zero-no-soa-ttl-cache <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> resolver-query-timeout <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> deny-answer-addresses { <em class="replaceable"><code>address_match_list</code></em> } [<span class="optional"> except-from { <em class="replaceable"><code>namelist</code></em> } </span>];</span>]
    [<span class="optional"> deny-answer-aliases { <em class="replaceable"><code>namelist</code></em> } [<span class="optional"> except-from { <em class="replaceable"><code>namelist</code></em> } </span>];</span>]
    [<span class="optional"> rate-limit {
        [<span class="optional"> responses-per-second <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> referrals-per-second <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> nodata-per-second <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> nxdomains-per-second <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> errors-per-second <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> all-per-second <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> window <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> log-only <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
        [<span class="optional"> qps-scale <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> ipv4-prefix-length <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> ipv6-prefix-length <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> slip <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> exempt-clients  { <em class="replaceable"><code>address_match_list</code></em> } ; </span>]
        [<span class="optional"> max-table-size <em class="replaceable"><code>number</code></em> ; </span>]
        [<span class="optional"> min-table-size <em class="replaceable"><code>number</code></em> ; </span>]
      } ; </span>]
    [<span class="optional"> response-policy {
        zone <em class="replaceable"><code>zone_name</code></em>
        [<span class="optional"> policy <em class="replaceable"><code>(given | disabled | passthru |
                  nxdomain | nodata | cname domain</code></em>) </span>]
        [<span class="optional"> recursive-only <em class="replaceable"><code>yes_or_no</code></em> </span>]
        [<span class="optional"> max-policy-ttl <em class="replaceable"><code>number</code></em> </span>]
        [<span class="optional"> break-dnssec <em class="replaceable"><code>yes_or_no</code></em> </span>]
        [<span class="optional"> min-ns-dots <em class="replaceable"><code>number</code></em> </span>]
        ; [<span class="optional">...</span>]
    } ; </span>]
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="options"></a><span><strong class="command">options</strong></span> Statement Definition and
          Usage</h3></div></div></div>
<p>
          The <span><strong class="command">options</strong></span> statement sets up global
          options
          to be used by <acronym class="acronym">BIND</acronym>. This statement
          may appear only
          once in a configuration file. If there is no <span><strong class="command">options</strong></span>
          statement, an options block with each option set to its default will
          be used.
        </p>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">attach-cache</strong></span></span></dt>
<dd>
<p>
                  Allows multiple views to share a single cache
                  database.
                  Each view has its own cache database by default, but
                  if multiple views have the same operational policy
                  for name resolution and caching, those views can
                  share a single cache to save memory and possibly
                  improve resolution efficiency by using this option.
                </p>
<p>
                  The <span><strong class="command">attach-cache</strong></span> option
                  may also be specified in <span><strong class="command">view</strong></span>
                  statements, in which case it overrides the
                  global <span><strong class="command">attach-cache</strong></span> option.
                </p>
<p>
                  The <em class="replaceable"><code>cache_name</code></em> specifies
                  the cache to be shared.
                  When the <span><strong class="command">named</strong></span> server configures
                  views which are supposed to share a cache, it
                  creates a cache with the specified name for the
                  first view of these sharing views.
                  The rest of the views will simply refer to the
                  already created cache.
                </p>
<p>
                  One common configuration to share a cache would be to
                  allow all views to share a single cache.
                  This can be done by specifying
                  the <span><strong class="command">attach-cache</strong></span> as a global
                  option with an arbitrary name.
                </p>
<p>
                  Another possible operation is to allow a subset of
                  all views to share a cache while the others to
                  retain their own caches.
                  For example, if there are three views A, B, and C,
                  and only A and B should share a cache, specify the
                  <span><strong class="command">attach-cache</strong></span> option as a view A (or
                  B)'s option, referring to the other view name:
                </p>
<pre class="programlisting">
  view "A" {
    // this view has its own cache
    ...
  };
  view "B" {
    // this view refers to A's cache
    attach-cache "A";
  };
  view "C" {
    // this view has its own cache
    ...
  };
</pre>
<p>
                  Views that share a cache must have the same policy
                  on configurable parameters that may affect caching.
                  The current implementation requires the following
                  configurable options be consistent among these
                  views:
                  <span><strong class="command">check-names</strong></span>,
                  <span><strong class="command">cleaning-interval</strong></span>,
                  <span><strong class="command">dnssec-accept-expired</strong></span>,
                  <span><strong class="command">dnssec-validation</strong></span>,
                  <span><strong class="command">max-cache-ttl</strong></span>,
                  <span><strong class="command">max-ncache-ttl</strong></span>,
                  <span><strong class="command">max-cache-size</strong></span>, and
                  <span><strong class="command">zero-no-soa-ttl</strong></span>.
                </p>
<p>
                  Note that there may be other parameters that may
                  cause confusion if they are inconsistent for
                  different views that share a single cache.
                  For example, if these views define different sets of
                  forwarders that can return different answers for the
                  same question, sharing the answer does not make
                  sense or could even be harmful.
                  It is administrator's responsibility to ensure
                  configuration differences in different views do
                  not cause disruption with a shared cache.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">directory</strong></span></span></dt>
<dd><p>
                The working directory of the server.
                Any non-absolute pathnames in the configuration file will be
                taken
                as relative to this directory. The default location for most
                server
                output files (e.g. <code class="filename">named.run</code>)
                is this directory.
                If a directory is not specified, the working directory
                defaults to `<code class="filename">.</code>', the directory from
                which the server
                was started. The directory specified should be an absolute
                path.
              </p></dd>
<dt><span class="term"><span><strong class="command">key-directory</strong></span></span></dt>
<dd><p>
                When performing dynamic update of secure zones, the
                directory where the public and private DNSSEC key files
                should be found, if different than the current working
                directory.  (Note that this option has no effect on the
                paths for files containing non-DNSSEC keys such as
                <code class="filename">bind.keys</code>,
                <code class="filename">rndc.key</code> or
                <code class="filename">session.key</code>.)
              </p></dd>
<dt><span class="term"><span><strong class="command">managed-keys-directory</strong></span></span></dt>
<dd>
<p>
                Specifies the directory in which to store the files that
                track managed DNSSEC keys.  By default, this is the working
                directory.
              </p>
<p>
                If <span><strong class="command">named</strong></span> is not configured to use views,
                then managed keys for the server will be tracked in a single
                file called <code class="filename">managed-keys.bind</code>.
                Otherwise, managed keys will be tracked in separate files,
                one file per view; each file name will be the SHA256 hash
                of the view name, followed by the extension
                <code class="filename">.mkeys</code>.
              </p>
</dd>
<dt><span class="term"><span><strong class="command">named-xfer</strong></span></span></dt>
<dd><p>
                <span class="emphasis"><em>This option is obsolete.</em></span> It
                was used in <acronym class="acronym">BIND</acronym> 8 to specify
                the pathname to the <span><strong class="command">named-xfer</strong></span>
                program.  In <acronym class="acronym">BIND</acronym> 9, no separate
                <span><strong class="command">named-xfer</strong></span> program is needed;
                its functionality is built into the name server.
              </p></dd>
<dt><span class="term"><span><strong class="command">tkey-gssapi-keytab</strong></span></span></dt>
<dd><p>
                The KRB5 keytab file to use for GSS-TSIG updates. If
                this option is set and tkey-gssapi-credential is not
                set, then updates will be allowed with any key
                matching a principal in the specified keytab.
              </p></dd>
<dt><span class="term"><span><strong class="command">tkey-gssapi-credential</strong></span></span></dt>
<dd><p>
                The security credential with which the server should
                authenticate keys requested by the GSS-TSIG protocol.
                Currently only Kerberos 5 authentication is available
                and the credential is a Kerberos principal which the
                server can acquire through the default system key
                file, normally <code class="filename">/etc/krb5.keytab</code>.
                The location keytab file can be overridden using the
                tkey-gssapi-keytab option. Normally this principal is
                of the form "<strong class="userinput"><code>DNS/</code></strong><code class="varname">server.domain</code>".
                To use GSS-TSIG, <span><strong class="command">tkey-domain</strong></span> must
                also be set if a specific keytab is not set with
                tkey-gssapi-keytab.
              </p></dd>
<dt><span class="term"><span><strong class="command">tkey-domain</strong></span></span></dt>
<dd><p>
                The domain appended to the names of all shared keys
                generated with <span><strong class="command">TKEY</strong></span>.  When a
                client requests a <span><strong class="command">TKEY</strong></span> exchange,
                it may or may not specify the desired name for the
                key. If present, the name of the shared key will
                be <code class="varname">client specified part</code> +
                <code class="varname">tkey-domain</code>.  Otherwise, the
                name of the shared key will be <code class="varname">random hex
                digits</code> + <code class="varname">tkey-domain</code>.
                In most cases, the <span><strong class="command">domainname</strong></span>
                should be the server's domain name, or an otherwise
                non-existent subdomain like
                "_tkey.<code class="varname">domainname</code>".  If you are
                using GSS-TSIG, this variable must be defined, unless
                you specify a specific keytab using tkey-gssapi-keytab.
              </p></dd>
<dt><span class="term"><span><strong class="command">tkey-dhkey</strong></span></span></dt>
<dd><p>
                The Diffie-Hellman key used by the server
                to generate shared keys with clients using the Diffie-Hellman
                mode
                of <span><strong class="command">TKEY</strong></span>. The server must be
                able to load the
                public and private keys from files in the working directory.
                In
                most cases, the keyname should be the server's host name.
              </p></dd>
<dt><span class="term"><span><strong class="command">cache-file</strong></span></span></dt>
<dd><p>
                This is for testing only.  Do not use.
              </p></dd>
<dt><span class="term"><span><strong class="command">dump-file</strong></span></span></dt>
<dd><p>
                The pathname of the file the server dumps
                the database to when instructed to do so with
                <span><strong class="command">rndc dumpdb</strong></span>.
                If not specified, the default is <code class="filename">named_dump.db</code>.
              </p></dd>
<dt><span class="term"><span><strong class="command">memstatistics-file</strong></span></span></dt>
<dd><p>
                The pathname of the file the server writes memory
                usage statistics to on exit. If not specified,
                the default is <code class="filename">named.memstats</code>.
              </p></dd>
<dt><span class="term"><span><strong class="command">pid-file</strong></span></span></dt>
<dd><p>
                The pathname of the file the server writes its process ID
                in. If not specified, the default is
                <code class="filename">/var/run/named/named.pid</code>.
                The PID file is used by programs that want to send signals to
                the running
                name server. Specifying <span><strong class="command">pid-file none</strong></span> disables the
                use of a PID file &#8212; no file will be written and any
                existing one will be removed.  Note that <span><strong class="command">none</strong></span>
                is a keyword, not a filename, and therefore is not enclosed
                in
                double quotes.
              </p></dd>
<dt><span class="term"><span><strong class="command">recursing-file</strong></span></span></dt>
<dd><p>
                The pathname of the file the server dumps
                the queries that are currently recursing when instructed
                to do so with <span><strong class="command">rndc recursing</strong></span>.
                If not specified, the default is <code class="filename">named.recursing</code>.
              </p></dd>
<dt><span class="term"><span><strong class="command">statistics-file</strong></span></span></dt>
<dd><p>
                The pathname of the file the server appends statistics
                to when instructed to do so using <span><strong class="command">rndc stats</strong></span>.
                If not specified, the default is <code class="filename">named.stats</code> in the
                server's current directory.  The format of the file is
                described
                in <a href="Bv9ARM.ch06.html#statsfile" title="The Statistics File">the section called &#8220;The Statistics File&#8221;</a>.
              </p></dd>
<dt><span class="term"><span><strong class="command">bindkeys-file</strong></span></span></dt>
<dd><p>
                The pathname of a file to override the built-in trusted
                keys provided by <span><strong class="command">named</strong></span>.
                See the discussion of <span><strong class="command">dnssec-lookaside</strong></span>
                and <span><strong class="command">dnssec-validation</strong></span> for details. 
                If not specified, the default is
                <code class="filename">/etc/bind.keys</code>.
              </p></dd>
<dt><span class="term"><span><strong class="command">secroots-file</strong></span></span></dt>
<dd><p>
                The pathname of the file the server dumps
                security roots to when instructed to do so with
                <span><strong class="command">rndc secroots</strong></span>.
                If not specified, the default is
                <code class="filename">named.secroots</code>.
              </p></dd>
<dt><span class="term"><span><strong class="command">session-keyfile</strong></span></span></dt>
<dd><p>
                The pathname of the file into which to write a TSIG
                session key generated by <span><strong class="command">named</strong></span> for use by
                <span><strong class="command">nsupdate -l</strong></span>.  If not specified, the
                default is <code class="filename">/var/run/named/session.key</code>.
                (See <a href="Bv9ARM.ch06.html#dynamic_update_policies" title="Dynamic Update Policies">the section called &#8220;Dynamic Update Policies&#8221;</a>, and in
                particular the discussion of the
                <span><strong class="command">update-policy</strong></span> statement's
                <strong class="userinput"><code>local</code></strong> option for more
                information about this feature.)
              </p></dd>
<dt><span class="term"><span><strong class="command">session-keyname</strong></span></span></dt>
<dd><p>
                The key name to use for the TSIG session key.
                If not specified, the default is "local-ddns".
              </p></dd>
<dt><span class="term"><span><strong class="command">session-keyalg</strong></span></span></dt>
<dd><p>
                The algorithm to use for the TSIG session key.
                Valid values are hmac-sha1, hmac-sha224, hmac-sha256,
                hmac-sha384, hmac-sha512 and hmac-md5.  If not
                specified, the default is hmac-sha256.
              </p></dd>
<dt><span class="term"><span><strong class="command">port</strong></span></span></dt>
<dd><p>
                The UDP/TCP port number the server uses for
                receiving and sending DNS protocol traffic.
                The default is 53.  This option is mainly intended for server
                testing;
                a server using a port other than 53 will not be able to
                communicate with
                the global DNS.
              </p></dd>
<dt><span class="term"><span><strong class="command">random-device</strong></span></span></dt>
<dd><p>
                The source of entropy to be used by the server.  Entropy is
                primarily needed
                for DNSSEC operations, such as TKEY transactions and dynamic
                update of signed
                zones.  This options specifies the device (or file) from which
                to read
                entropy.  If this is a file, operations requiring entropy will
                fail when the
                file has been exhausted.  If not specified, the default value
                is
                <code class="filename">/dev/random</code>
                (or equivalent) when present, and none otherwise.  The
                <span><strong class="command">random-device</strong></span> option takes
                effect during
                the initial configuration load at server startup time and
                is ignored on subsequent reloads.
              </p></dd>
<dt><span class="term"><span><strong class="command">preferred-glue</strong></span></span></dt>
<dd><p>
                If specified, the listed type (A or AAAA) will be emitted
                before other glue
                in the additional section of a query response.
                The default is not to prefer any type (NONE).
              </p></dd>
<dt>
<a name="root_delegation_only"></a><span class="term"><span><strong class="command">root-delegation-only</strong></span></span>
</dt>
<dd>
<p>
                Turn on enforcement of delegation-only in TLDs
                (top level domains) and root zones with an optional
                exclude list.
              </p>
<p>
                DS queries are expected to be made to and be answered by
                delegation only zones.  Such queries and responses are
                treated as an exception to delegation-only processing
                and are not converted to NXDOMAIN responses provided
                a CNAME is not discovered at the query name.
              </p>
<p>
                If a delegation only zone server also serves a child
                zone it is not always possible to determine whether
                an answer comes from the delegation only zone or the
                child zone.  SOA NS and DNSKEY records are apex
                only records and a matching response that contains
                these records or DS is treated as coming from a
                child zone.  RRSIG records are also examined to see
                if they are signed by a child zone or not.  The
                authority section is also examined to see if there
                is evidence that the answer is from the child zone.
                Answers that are determined to be from a child zone
                are not converted to NXDOMAIN responses.  Despite
                all these checks there is still a possibility of
                false negatives when a child zone is being served.
              </p>
<p>
                Similarly false positives can arise from empty nodes
                (no records at the name) in the delegation only zone
                when the query type is not ANY.
              </p>
<p>
                Note some TLDs are not delegation only (e.g. "DE", "LV",
                "US" and "MUSEUM").  This list is not exhaustive.
              </p>
<pre class="programlisting">
options {
        root-delegation-only exclude { "de"; "lv"; "us"; "museum"; };
};
</pre>
</dd>
<dt><span class="term"><span><strong class="command">disable-algorithms</strong></span></span></dt>
<dd><p>
                Disable the specified DNSSEC algorithms at and below the
                specified name.
                Multiple <span><strong class="command">disable-algorithms</strong></span>
                statements are allowed.
                Only the most specific will be applied.
              </p></dd>
<dt><span class="term"><span><strong class="command">dnssec-lookaside</strong></span></span></dt>
<dd>
<p>
                When set, <span><strong class="command">dnssec-lookaside</strong></span> provides the
                validator with an alternate method to validate DNSKEY
                records at the top of a zone.  When a DNSKEY is at or
                below a domain specified by the deepest
                <span><strong class="command">dnssec-lookaside</strong></span>, and the normal DNSSEC
                validation has left the key untrusted, the trust-anchor
                will be appended to the key name and a DLV record will be
                looked up to see if it can validate the key.  If the DLV
                record validates a DNSKEY (similarly to the way a DS
                record does) the DNSKEY RRset is deemed to be trusted.
              </p>
<p>
                If <span><strong class="command">dnssec-lookaside</strong></span> is set to
                <strong class="userinput"><code>auto</code></strong>, then built-in default
                values for the DLV domain and trust anchor will be
                used, along with a built-in key for validation.
              </p>
<p>
                If <span><strong class="command">dnssec-lookaside</strong></span> is set to
                <strong class="userinput"><code>no</code></strong>, then dnssec-lookaside
                is not used.
              </p>
<p>
                The default DLV key is stored in the file
                <code class="filename">bind.keys</code>;
                <span><strong class="command">named</strong></span> will load that key at
                startup if <span><strong class="command">dnssec-lookaside</strong></span> is set to
                <code class="constant">auto</code>.  A copy of the file is
                installed along with <acronym class="acronym">BIND</acronym> 9, and is
                current as of the release date.  If the DLV key expires, a
                new copy of <code class="filename">bind.keys</code> can be downloaded
                from <a href="https://www.isc.org/solutions/dlv/" target="_top">https://www.isc.org/solutions/dlv/</a>.
              </p>
<p>
                (To prevent problems if <code class="filename">bind.keys</code> is
                not found, the current key is also compiled in to
                <span><strong class="command">named</strong></span>.  Relying on this is not
                recommended, however, as it requires <span><strong class="command">named</strong></span>
                to be recompiled with a new key when the DLV key expires.)
              </p>
<p>
                NOTE: <span><strong class="command">named</strong></span> only loads certain specific
                keys from <code class="filename">bind.keys</code>:  those for the
                DLV zone and for the DNS root zone.  The file cannot be
                used to store keys for other zones.
              </p>
</dd>
<dt><span class="term"><span><strong class="command">dnssec-must-be-secure</strong></span></span></dt>
<dd><p>
                Specify hierarchies which must be or may not be secure
                (signed and validated).  If <strong class="userinput"><code>yes</code></strong>,
                then <span><strong class="command">named</strong></span> will only accept answers if
                they are secure.  If <strong class="userinput"><code>no</code></strong>, then normal
                DNSSEC validation applies allowing for insecure answers to
                be accepted.  The specified domain must be under a
                <span><strong class="command">trusted-keys</strong></span> or
                <span><strong class="command">managed-keys</strong></span> statement, or
                <span><strong class="command">dnssec-lookaside</strong></span> must be active.
              </p></dd>
<dt><span class="term"><span><strong class="command">dns64</strong></span></span></dt>
<dd>
<p>
                This directive instructs <span><strong class="command">named</strong></span> to
                return mapped IPv4 addresses to AAAA queries when
                there are no AAAA records.  It is intended to be
                used in conjunction with a NAT64.  Each
                <span><strong class="command">dns64</strong></span> defines one DNS64 prefix.
                Multiple DNS64 prefixes can be defined.
              </p>
<p>
                Compatible IPv6 prefixes have lengths of 32, 40, 48, 56,
                64 and 96 as per RFC 6052.
              </p>
<p>
                Additionally a reverse IP6.ARPA zone will be created for
                the prefix to provide a mapping from the IP6.ARPA names
                to the corresponding IN-ADDR.ARPA names using synthesized
                CNAMEs.  <span><strong class="command">dns64-server</strong></span> and
                <span><strong class="command">dns64-contact</strong></span> can be used to specify
                the name of the server and contact for the zones. These
                are settable at the view / options level.  These are
                not settable on a per-prefix basis.
              </p>
<p>
                Each <span><strong class="command">dns64</strong></span> supports an optional
                <span><strong class="command">clients</strong></span> ACL that determines which
                clients are affected by this directive.  If not defined,
                it defaults to <strong class="userinput"><code>any;</code></strong>.
              </p>
<p>
                Each <span><strong class="command">dns64</strong></span> supports an optional
                <span><strong class="command">mapped</strong></span> ACL that selects which
                IPv4 addresses are to be mapped in the corresponding    
                A RRset.  If not defined it defaults to
                <strong class="userinput"><code>any;</code></strong>.
              </p>
<p>
                Normally, DNS64 won't apply to a domain name that
                owns one or more AAAA records; these records will
                simply be returned.  The optional
                <span><strong class="command">exclude</strong></span> ACL allows specification
                of a list of IPv6 addresses that will be ignored
                if they appear in a domain name's AAAA records, and
                DNS64 will be applied to any A records the domain
                name owns.  If not defined, <span><strong class="command">exclude</strong></span>
                defaults to none.
              </p>
<p>
                A optional <span><strong class="command">suffix</strong></span> can also
                be defined to set the bits trailing the mapped
                IPv4 address bits.  By default these bits are
                set to <strong class="userinput"><code>::</code></strong>.  The bits
                matching the prefix and mapped IPv4 address
                must be zero.
              </p>
<p>
                If <span><strong class="command">recursive-only</strong></span> is set to
                <span><strong class="command">yes</strong></span> the DNS64 synthesis will
                only happen for recursive queries.  The default
                is <span><strong class="command">no</strong></span>.
              </p>
<p>
                If <span><strong class="command">break-dnssec</strong></span> is set to
                <span><strong class="command">yes</strong></span> the DNS64 synthesis will
                happen even if the result, if validated, would
                cause a DNSSEC validation failure.  If this option
                is set to <span><strong class="command">no</strong></span> (the default), the DO
                is set on the incoming query, and there are RRSIGs on
                the applicable records, then synthesis will not happen.
              </p>
<pre class="programlisting">
        acl rfc1918 { 10/8; 192.168/16; 172.16/12; };

        dns64 64:FF9B::/96 {
                clients { any; };
                mapped { !rfc1918; any; };
                exclude { 64:FF9B::/96; ::ffff:0000:0000/96; };
                suffix ::;
        };
</pre>
</dd>
<dt><span class="term"><span><strong class="command">dnssec-update-mode</strong></span></span></dt>
<dd>
<p>
                  If this option is set to its default value of
                  <code class="literal">maintain</code> in a zone of type
                  <code class="literal">master</code> which is DNSSEC-signed
                  and configured to allow dynamic updates (see
                  <a href="Bv9ARM.ch06.html#dynamic_update_policies" title="Dynamic Update Policies">the section called &#8220;Dynamic Update Policies&#8221;</a>), and
                  if <span><strong class="command">named</strong></span> has access to the
                  private signing key(s) for the zone, then
                  <span><strong class="command">named</strong></span> will automatically sign all new
                  or changed records and maintain signatures for the zone
                  by regenerating RRSIG records whenever they approach
                  their expiration date.
                </p>
<p>
                  If the option is changed to <code class="literal">no-resign</code>,
                  then <span><strong class="command">named</strong></span> will sign all new or
                  changed records, but scheduled maintenance of
                  signatures is disabled.
                </p>
<p>
                  With either of these settings, <span><strong class="command">named</strong></span>
                  will reject updates to a DNSSEC-signed zone when the
                  signing keys are inactive or unavailable to
                  <span><strong class="command">named</strong></span>.  (A planned third option,
                  <code class="literal">external</code>, will disable all automatic
                  signing and allow DNSSEC data to be submitted into a zone
                  via dynamic update; this is not yet implemented.)
                </p>
</dd>
<dt><span class="term"><span><strong class="command">zone-statistics</strong></span></span></dt>
<dd>
<p>
                If <strong class="userinput"><code>full</code></strong>, the server will collect
                statistical data on all zones (unless specifically
                turned off on a per-zone basis by specifying
                <span><strong class="command">zone-statistics terse</strong></span> or
                <span><strong class="command">zone-statistics none</strong></span>
                in the <span><strong class="command">zone</strong></span> statement).
                The default is <strong class="userinput"><code>terse</code></strong>, providing
                minimal statistics on zones (including name and
                current serial number, but not query type
                counters).
              </p>
<p>
                These statistics may be accessed via the
                <span><strong class="command">statistics-channel</strong></span> or
                using <span><strong class="command">rndc stats</strong></span>, which
                will dump them to the file listed
                in the <span><strong class="command">statistics-file</strong></span>.  See
                also <a href="Bv9ARM.ch06.html#statsfile" title="The Statistics File">the section called &#8220;The Statistics File&#8221;</a>.
              </p>
<p>
                For backward compatibility with earlier versions
                of BIND 9, the <span><strong class="command">zone-statistics</strong></span>
                option can also accept <strong class="userinput"><code>yes</code></strong>
                or <strong class="userinput"><code>no</code></strong>, which have the same
                effect as <strong class="userinput"><code>full</code></strong> and
                <strong class="userinput"><code>terse</code></strong>, respectively.
                </p>
</dd>
</dl></div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="boolean_options"></a>Boolean Options</h4></div></div></div>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">allow-new-zones</strong></span></span></dt>
<dd><p>
                  If <strong class="userinput"><code>yes</code></strong>, then zones can be
                  added at runtime via <span><strong class="command">rndc addzone</strong></span>
                  or deleted via <span><strong class="command">rndc delzone</strong></span>.
                  The default is <strong class="userinput"><code>no</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">auth-nxdomain</strong></span></span></dt>
<dd><p>
                  If <strong class="userinput"><code>yes</code></strong>, then the <span><strong class="command">AA</strong></span> bit
                  is always set on NXDOMAIN responses, even if the server is
                  not actually
                  authoritative. The default is <strong class="userinput"><code>no</code></strong>;
                  this is
                  a change from <acronym class="acronym">BIND</acronym> 8. If you
                  are using very old DNS software, you
                  may need to set it to <strong class="userinput"><code>yes</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">deallocate-on-exit</strong></span></span></dt>
<dd><p>
                  This option was used in <acronym class="acronym">BIND</acronym>
                  8 to enable checking
                  for memory leaks on exit. <acronym class="acronym">BIND</acronym> 9 ignores the option and always performs
                  the checks.
                </p></dd>
<dt><span class="term"><span><strong class="command">memstatistics</strong></span></span></dt>
<dd><p>
                  Write memory statistics to the file specified by
                  <span><strong class="command">memstatistics-file</strong></span> at exit.
                  The default is <strong class="userinput"><code>no</code></strong> unless
                  '-m record' is specified on the command line in
                  which case it is <strong class="userinput"><code>yes</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">dialup</strong></span></span></dt>
<dd>
<p>
                  If <strong class="userinput"><code>yes</code></strong>, then the
                  server treats all zones as if they are doing zone transfers
                  across
                  a dial-on-demand dialup link, which can be brought up by
                  traffic
                  originating from this server. This has different effects
                  according
                  to zone type and concentrates the zone maintenance so that
                  it all
                  happens in a short interval, once every <span><strong class="command">heartbeat-interval</strong></span> and
                  hopefully during the one call. It also suppresses some of
                  the normal
                  zone maintenance traffic. The default is <strong class="userinput"><code>no</code></strong>.
                </p>
<p>
                  The <span><strong class="command">dialup</strong></span> option
                  may also be specified in the <span><strong class="command">view</strong></span> and
                  <span><strong class="command">zone</strong></span> statements,
                  in which case it overrides the global <span><strong class="command">dialup</strong></span>
                  option.
                </p>
<p>
                  If the zone is a master zone, then the server will send out a
                  NOTIFY
                  request to all the slaves (default). This should trigger the
                  zone serial
                  number check in the slave (providing it supports NOTIFY)
                  allowing the slave
                  to verify the zone while the connection is active.
                  The set of servers to which NOTIFY is sent can be controlled
                  by
                  <span><strong class="command">notify</strong></span> and <span><strong class="command">also-notify</strong></span>.
                </p>
<p>
                  If the
                  zone is a slave or stub zone, then the server will suppress
                  the regular
                  "zone up to date" (refresh) queries and only perform them
                  when the
                  <span><strong class="command">heartbeat-interval</strong></span> expires in
                  addition to sending
                  NOTIFY requests.
                </p>
<p>
                  Finer control can be achieved by using
                  <strong class="userinput"><code>notify</code></strong> which only sends NOTIFY
                  messages,
                  <strong class="userinput"><code>notify-passive</code></strong> which sends NOTIFY
                  messages and
                  suppresses the normal refresh queries, <strong class="userinput"><code>refresh</code></strong>
                  which suppresses normal refresh processing and sends refresh
                  queries
                  when the <span><strong class="command">heartbeat-interval</strong></span>
                  expires, and
                  <strong class="userinput"><code>passive</code></strong> which just disables normal
                  refresh
                  processing.
                </p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                          <p>
                            dialup mode
                          </p>
                        </td>
<td>
                          <p>
                            normal refresh
                          </p>
                        </td>
<td>
                          <p>
                            heart-beat refresh
                          </p>
                        </td>
<td>
                          <p>
                            heart-beat notify
                          </p>
                        </td>
</tr>
<tr>
<td>
                          <p><span><strong class="command">no</strong></span> (default)</p>
                        </td>
<td>
                          <p>
                            yes
                          </p>
                        </td>
<td>
                          <p>
                            no
                          </p>
                        </td>
<td>
                          <p>
                            no
                          </p>
                        </td>
</tr>
<tr>
<td>
                          <p><span><strong class="command">yes</strong></span></p>
                        </td>
<td>
                          <p>
                            no
                          </p>
                        </td>
<td>
                          <p>
                            yes
                          </p>
                        </td>
<td>
                          <p>
                            yes
                          </p>
                        </td>
</tr>
<tr>
<td>
                          <p><span><strong class="command">notify</strong></span></p>
                        </td>
<td>
                          <p>
                            yes
                          </p>
                        </td>
<td>
                          <p>
                            no
                          </p>
                        </td>
<td>
                          <p>
                            yes
                          </p>
                        </td>
</tr>
<tr>
<td>
                          <p><span><strong class="command">refresh</strong></span></p>
                        </td>
<td>
                          <p>
                            no
                          </p>
                        </td>
<td>
                          <p>
                            yes
                          </p>
                        </td>
<td>
                          <p>
                            no
                          </p>
                        </td>
</tr>
<tr>
<td>
                          <p><span><strong class="command">passive</strong></span></p>
                        </td>
<td>
                          <p>
                            no
                          </p>
                        </td>
<td>
                          <p>
                            no
                          </p>
                        </td>
<td>
                          <p>
                            no
                          </p>
                        </td>
</tr>
<tr>
<td>
                          <p><span><strong class="command">notify-passive</strong></span></p>
                        </td>
<td>
                          <p>
                            no
                          </p>
                        </td>
<td>
                          <p>
                            no
                          </p>
                        </td>
<td>
                          <p>
                            yes
                          </p>
                        </td>
</tr>
</tbody>
</table></div>
<p>
                  Note that normal NOTIFY processing is not affected by
                  <span><strong class="command">dialup</strong></span>.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">fake-iquery</strong></span></span></dt>
<dd><p>
                  In <acronym class="acronym">BIND</acronym> 8, this option
                  enabled simulating the obsolete DNS query type
                  IQUERY. <acronym class="acronym">BIND</acronym> 9 never does
                  IQUERY simulation.
                </p></dd>
<dt><span class="term"><span><strong class="command">fetch-glue</strong></span></span></dt>
<dd><p>
                  This option is obsolete.
                  In BIND 8, <strong class="userinput"><code>fetch-glue yes</code></strong>
                  caused the server to attempt to fetch glue resource records
                  it
                  didn't have when constructing the additional
                  data section of a response.  This is now considered a bad
                  idea
                  and BIND 9 never does it.
                </p></dd>
<dt><span class="term"><span><strong class="command">flush-zones-on-shutdown</strong></span></span></dt>
<dd><p>
                  When the nameserver exits due receiving SIGTERM,
                  flush or do not flush any pending zone writes.  The default
                  is
                  <span><strong class="command">flush-zones-on-shutdown</strong></span> <strong class="userinput"><code>no</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">has-old-clients</strong></span></span></dt>
<dd><p>
                  This option was incorrectly implemented
                  in <acronym class="acronym">BIND</acronym> 8, and is ignored by <acronym class="acronym">BIND</acronym> 9.
                  To achieve the intended effect
                  of
                  <span><strong class="command">has-old-clients</strong></span> <strong class="userinput"><code>yes</code></strong>, specify
                  the two separate options <span><strong class="command">auth-nxdomain</strong></span> <strong class="userinput"><code>yes</code></strong>
                  and <span><strong class="command">rfc2308-type1</strong></span> <strong class="userinput"><code>no</code></strong> instead.
                </p></dd>
<dt><span class="term"><span><strong class="command">host-statistics</strong></span></span></dt>
<dd><p>
                  In BIND 8, this enables keeping of
                  statistics for every host that the name server interacts
                  with.
                  Not implemented in BIND 9.
                </p></dd>
<dt><span class="term"><span><strong class="command">maintain-ixfr-base</strong></span></span></dt>
<dd><p>
                  <span class="emphasis"><em>This option is obsolete</em></span>.
                  It was used in <acronym class="acronym">BIND</acronym> 8 to
                  determine whether a transaction log was
                  kept for Incremental Zone Transfer. <acronym class="acronym">BIND</acronym> 9 maintains a transaction
                  log whenever possible.  If you need to disable outgoing
                  incremental zone
                  transfers, use <span><strong class="command">provide-ixfr</strong></span> <strong class="userinput"><code>no</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">minimal-responses</strong></span></span></dt>
<dd><p>
                  If <strong class="userinput"><code>yes</code></strong>, then when generating
                  responses the server will only add records to the authority
                  and additional data sections when they are required (e.g.
                  delegations, negative responses).  This may improve the
                  performance of the server.
                  The default is <strong class="userinput"><code>no</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">multiple-cnames</strong></span></span></dt>
<dd><p>
                  This option was used in <acronym class="acronym">BIND</acronym> 8 to allow
                  a domain name to have multiple CNAME records in violation of
                  the DNS standards.  <acronym class="acronym">BIND</acronym> 9.2 onwards
                  always strictly enforces the CNAME rules both in master
                  files and dynamic updates.
                </p></dd>
<dt><span class="term"><span><strong class="command">notify</strong></span></span></dt>
<dd>
<p>
                  If <strong class="userinput"><code>yes</code></strong> (the default),
                  DNS NOTIFY messages are sent when a zone the server is
                  authoritative for
                  changes, see <a href="Bv9ARM.ch04.html#notify" title="Notify">the section called &#8220;Notify&#8221;</a>.  The messages are
                  sent to the
                  servers listed in the zone's NS records (except the master
                  server identified
                  in the SOA MNAME field), and to any servers listed in the
                  <span><strong class="command">also-notify</strong></span> option.
                </p>
<p>
                  If <strong class="userinput"><code>master-only</code></strong>, notifies are only
                  sent
                  for master zones.
                  If <strong class="userinput"><code>explicit</code></strong>, notifies are sent only
                  to
                  servers explicitly listed using <span><strong class="command">also-notify</strong></span>.
                  If <strong class="userinput"><code>no</code></strong>, no notifies are sent.
                </p>
<p>
                  The <span><strong class="command">notify</strong></span> option may also be
                  specified in the <span><strong class="command">zone</strong></span>
                  statement,
                  in which case it overrides the <span><strong class="command">options notify</strong></span> statement.
                  It would only be necessary to turn off this option if it
                  caused slaves
                  to crash.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">notify-to-soa</strong></span></span></dt>
<dd><p>
                  If <strong class="userinput"><code>yes</code></strong> do not check the nameservers
                  in the NS RRset against the SOA MNAME.  Normally a NOTIFY
                  message is not sent to the SOA MNAME (SOA ORIGIN) as it is
                  supposed to contain the name of the ultimate master.
                  Sometimes, however, a slave is listed as the SOA MNAME in
                  hidden master configurations and in that case you would
                  want the ultimate master to still send NOTIFY messages to
                  all the nameservers listed in the NS RRset.
                </p></dd>
<dt><span class="term"><span><strong class="command">recursion</strong></span></span></dt>
<dd><p>
                  If <strong class="userinput"><code>yes</code></strong>, and a
                  DNS query requests recursion, then the server will attempt
                  to do
                  all the work required to answer the query. If recursion is
                  off
                  and the server does not already know the answer, it will
                  return a
                  referral response. The default is
                  <strong class="userinput"><code>yes</code></strong>.
                  Note that setting <span><strong class="command">recursion no</strong></span> does not prevent
                  clients from getting data from the server's cache; it only
                  prevents new data from being cached as an effect of client
                  queries.
                  Caching may still occur as an effect the server's internal
                  operation, such as NOTIFY address lookups.
                  See also <span><strong class="command">fetch-glue</strong></span> above.
                </p></dd>
<dt><span class="term"><span><strong class="command">request-nsid</strong></span></span></dt>
<dd><p>
                  If <strong class="userinput"><code>yes</code></strong>, then an empty EDNS(0)
                  NSID (Name Server Identifier) option is sent with all 
                  queries to authoritative name servers during iterative
                  resolution. If the authoritative server returns an NSID
                  option in its response, then its contents are logged in
                  the <span><strong class="command">resolver</strong></span> category at level
                  <span><strong class="command">info</strong></span>.
                  The default is <strong class="userinput"><code>no</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">rfc2308-type1</strong></span></span></dt>
<dd>
<p>
                  Setting this to <strong class="userinput"><code>yes</code></strong> will
                  cause the server to send NS records along with the SOA
                  record for negative
                  answers. The default is <strong class="userinput"><code>no</code></strong>.
                </p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
                    Not yet implemented in <acronym class="acronym">BIND</acronym>
                    9.
                  </p>
</div>
</dd>
<dt><span class="term"><span><strong class="command">use-id-pool</strong></span></span></dt>
<dd><p>
                  <span class="emphasis"><em>This option is obsolete</em></span>.
                  <acronym class="acronym">BIND</acronym> 9 always allocates query
                  IDs from a pool.
                </p></dd>
<dt><span class="term"><span><strong class="command">use-ixfr</strong></span></span></dt>
<dd><p>
                  <span class="emphasis"><em>This option is obsolete</em></span>.
                  If you need to disable IXFR to a particular server or
                  servers, see
                  the information on the <span><strong class="command">provide-ixfr</strong></span> option
                  in <a href="Bv9ARM.ch06.html#server_statement_definition_and_usage" title="server Statement Definition and
            Usage">the section called &#8220;<span><strong class="command">server</strong></span> Statement Definition and
            Usage&#8221;</a>.
                  See also
                  <a href="Bv9ARM.ch04.html#incremental_zone_transfers" title="Incremental Zone Transfers (IXFR)">the section called &#8220;Incremental Zone Transfers (IXFR)&#8221;</a>.
                </p></dd>
<dt><span class="term"><span><strong class="command">provide-ixfr</strong></span></span></dt>
<dd><p>
                  See the description of
                  <span><strong class="command">provide-ixfr</strong></span> in
                  <a href="Bv9ARM.ch06.html#server_statement_definition_and_usage" title="server Statement Definition and
            Usage">the section called &#8220;<span><strong class="command">server</strong></span> Statement Definition and
            Usage&#8221;</a>.
                </p></dd>
<dt><span class="term"><span><strong class="command">request-ixfr</strong></span></span></dt>
<dd><p>
                  See the description of
                  <span><strong class="command">request-ixfr</strong></span> in
                  <a href="Bv9ARM.ch06.html#server_statement_definition_and_usage" title="server Statement Definition and
            Usage">the section called &#8220;<span><strong class="command">server</strong></span> Statement Definition and
            Usage&#8221;</a>.
                </p></dd>
<dt><span class="term"><span><strong class="command">treat-cr-as-space</strong></span></span></dt>
<dd><p>
                  This option was used in <acronym class="acronym">BIND</acronym>
                  8 to make
                  the server treat carriage return ("<span><strong class="command">\r</strong></span>") characters the same way
                  as a space or tab character,
                  to facilitate loading of zone files on a UNIX system that
                  were generated
                  on an NT or DOS machine. In <acronym class="acronym">BIND</acronym> 9, both UNIX "<span><strong class="command">\n</strong></span>"
                  and NT/DOS "<span><strong class="command">\r\n</strong></span>" newlines
                  are always accepted,
                  and the option is ignored.
                </p></dd>
<dt>
<span class="term"><span><strong class="command">additional-from-auth</strong></span>, </span><span class="term"><span><strong class="command">additional-from-cache</strong></span></span>
</dt>
<dd>
<p>
                  These options control the behavior of an authoritative
                  server when
                  answering queries which have additional data, or when
                  following CNAME
                  and DNAME chains.
                </p>
<p>
                  When both of these options are set to <strong class="userinput"><code>yes</code></strong>
                  (the default) and a
                  query is being answered from authoritative data (a zone
                  configured into the server), the additional data section of
                  the
                  reply will be filled in using data from other authoritative
                  zones
                  and from the cache.  In some situations this is undesirable,
                  such
                  as when there is concern over the correctness of the cache,
                  or
                  in servers where slave zones may be added and modified by
                  untrusted third parties.  Also, avoiding
                  the search for this additional data will speed up server
                  operations
                  at the possible expense of additional queries to resolve
                  what would
                  otherwise be provided in the additional section.
                </p>
<p>
                  For example, if a query asks for an MX record for host <code class="literal">foo.example.com</code>,
                  and the record found is "<code class="literal">MX 10 mail.example.net</code>", normally the address
                  records (A and AAAA) for <code class="literal">mail.example.net</code> will be provided as well,
                  if known, even though they are not in the example.com zone.
                  Setting these options to <span><strong class="command">no</strong></span>
                  disables this behavior and makes
                  the server only search for additional data in the zone it
                  answers from.
                </p>
<p>
                  These options are intended for use in authoritative-only
                  servers, or in authoritative-only views.  Attempts to set
                  them to <span><strong class="command">no</strong></span> without also
                  specifying
                  <span><strong class="command">recursion no</strong></span> will cause the
                  server to
                  ignore the options and log a warning message.
                </p>
<p>
                  Specifying <span><strong class="command">additional-from-cache no</strong></span> actually
                  disables the use of the cache not only for additional data
                  lookups
                  but also when looking up the answer.  This is usually the
                  desired
                  behavior in an authoritative-only server where the
                  correctness of
                  the cached data is an issue.
                </p>
<p>
                  When a name server is non-recursively queried for a name
                  that is not
                  below the apex of any served zone, it normally answers with
                  an
                  "upwards referral" to the root servers or the servers of
                  some other
                  known parent of the query name.  Since the data in an
                  upwards referral
                  comes from the cache, the server will not be able to provide
                  upwards
                  referrals when <span><strong class="command">additional-from-cache no</strong></span>
                  has been specified.  Instead, it will respond to such
                  queries
                  with REFUSED.  This should not cause any problems since
                  upwards referrals are not required for the resolution
                  process.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">match-mapped-addresses</strong></span></span></dt>
<dd>
<p>
                  If <strong class="userinput"><code>yes</code></strong>, then an
                  IPv4-mapped IPv6 address will match any address match
                  list entries that match the corresponding IPv4 address.
                </p>
<p>
                  This option was introduced to work around a kernel quirk
                  in some operating systems that causes IPv4 TCP
                  connections, such as zone transfers, to be accepted on an
                  IPv6 socket using mapped addresses.  This caused address
                  match lists designed for IPv4 to fail to match.  However,
                  <span><strong class="command">named</strong></span> now solves this problem
                  internally.  The use of this option is discouraged.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">filter-aaaa-on-v4</strong></span></span></dt>
<dd>
<p>
                  This option is only available when
                  <acronym class="acronym">BIND</acronym> 9 is compiled with the
                  <strong class="userinput"><code>--enable-filter-aaaa</code></strong> option on the
                  "configure" command line.  It is intended to help the
                  transition from IPv4 to IPv6 by not giving IPv6 addresses
                  to DNS clients unless they have connections to the IPv6
                  Internet.  This is not recommended unless absolutely
                  necessary.  The default is <strong class="userinput"><code>no</code></strong>.
                  The <span><strong class="command">filter-aaaa-on-v4</strong></span> option
                  may also be specified in <span><strong class="command">view</strong></span> statements
                  to override the global <span><strong class="command">filter-aaaa-on-v4</strong></span>
                  option.
                </p>
<p>
                  If <strong class="userinput"><code>yes</code></strong>,
                  the DNS client is at an IPv4 address, in <span><strong class="command">filter-aaaa</strong></span>,
                  and if the response does not include DNSSEC signatures, 
                  then all AAAA records are deleted from the response.
                  This filtering applies to all responses and not only
                  authoritative responses.
                </p>
<p>
                  If <strong class="userinput"><code>break-dnssec</code></strong>,
                  then AAAA records are deleted even when dnssec is enabled.
                  As suggested by the name, this makes the response not verify,
                  because the DNSSEC protocol is designed detect deletions.
                </p>
<p>
                  This mechanism can erroneously cause other servers to 
                  not give AAAA records to their clients.  
                  A recursing server with both IPv6 and IPv4 network connections
                  that queries an authoritative server using this mechanism
                  via IPv4 will be denied AAAA records even if its client is
                  using IPv6.
                </p>
<p>
                  This mechanism is applied to authoritative as well as
                  non-authoritative records.
                  A client using IPv4 that is not allowed recursion can
                  erroneously be given AAAA records because the server is not
                  allowed to check for A records.
                </p>
<p>
                  Some AAAA records are given to IPv4 clients in glue records.
                  IPv4 clients that are servers can then erroneously
                  answer requests for AAAA records received via IPv4.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">ixfr-from-differences</strong></span></span></dt>
<dd>
<p>
                  When <strong class="userinput"><code>yes</code></strong> and the server loads a new
                  version of a master zone from its zone file or receives a
                  new version of a slave file via zone transfer, it will
                  compare the new version to the previous one and calculate
                  a set of differences.  The differences are then logged in
                  the zone's journal file such that the changes can be
                  transmitted to downstream slaves as an incremental zone
                  transfer.
                </p>
<p>
                  By allowing incremental zone transfers to be used for
                  non-dynamic zones, this option saves bandwidth at the
                  expense of increased CPU and memory consumption at the
                  master.
                  In particular, if the new version of a zone is completely
                  different from the previous one, the set of differences
                  will be of a size comparable to the combined size of the
                  old and new zone version, and the server will need to
                  temporarily allocate memory to hold this complete
                  difference set.
                </p>
<p><span><strong class="command">ixfr-from-differences</strong></span>
                  also accepts <span><strong class="command">master</strong></span> and
                  <span><strong class="command">slave</strong></span> at the view and options
                  levels which causes
                  <span><strong class="command">ixfr-from-differences</strong></span> to be enabled for
                  all <span><strong class="command">master</strong></span> or
                  <span><strong class="command">slave</strong></span> zones respectively.
                  It is off by default.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">multi-master</strong></span></span></dt>
<dd><p>
                  This should be set when you have multiple masters for a zone
                  and the
                  addresses refer to different machines.  If <strong class="userinput"><code>yes</code></strong>, <span><strong class="command">named</strong></span> will
                  not log
                  when the serial number on the master is less than what <span><strong class="command">named</strong></span>
                  currently
                  has.  The default is <strong class="userinput"><code>no</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">dnssec-enable</strong></span></span></dt>
<dd><p>
                  Enable DNSSEC support in <span><strong class="command">named</strong></span>.  Unless set to <strong class="userinput"><code>yes</code></strong>,
                  <span><strong class="command">named</strong></span> behaves as if it does not support DNSSEC.
                  The default is <strong class="userinput"><code>yes</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">dnssec-validation</strong></span></span></dt>
<dd><p>
                  Enable DNSSEC validation in <span><strong class="command">named</strong></span>.
                  Note <span><strong class="command">dnssec-enable</strong></span> also needs to be
                  set to <strong class="userinput"><code>yes</code></strong> to be effective.
                  If set to <strong class="userinput"><code>no</code></strong>, DNSSEC validation
                  is disabled.  If set to <strong class="userinput"><code>auto</code></strong>,
                  DNSSEC validation is enabled, and a default
                  trust-anchor for the DNS root zone is used.  If set to
                  <strong class="userinput"><code>yes</code></strong>, DNSSEC validation is enabled,
                  but a trust anchor must be manually configured using
                  a <span><strong class="command">trusted-keys</strong></span> or
                  <span><strong class="command">managed-keys</strong></span> statement.  The default
                  is <strong class="userinput"><code>yes</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">dnssec-accept-expired</strong></span></span></dt>
<dd><p>
                  Accept expired signatures when verifying DNSSEC signatures.
                  The default is <strong class="userinput"><code>no</code></strong>.
                  Setting this option to <strong class="userinput"><code>yes</code></strong>
                  leaves <span><strong class="command">named</strong></span> vulnerable to
                  replay attacks.
                </p></dd>
<dt><span class="term"><span><strong class="command">querylog</strong></span></span></dt>
<dd><p>
                  Specify whether query logging should be started when <span><strong class="command">named</strong></span>
                  starts.
                  If <span><strong class="command">querylog</strong></span> is not specified,
                  then the query logging
                  is determined by the presence of the logging category <span><strong class="command">queries</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">check-names</strong></span></span></dt>
<dd>
<p>
                  This option is used to restrict the character set and syntax
                  of
                  certain domain names in master files and/or DNS responses
                  received
                  from the network.  The default varies according to usage
                  area.  For
                  <span><strong class="command">master</strong></span> zones the default is <span><strong class="command">fail</strong></span>.
                  For <span><strong class="command">slave</strong></span> zones the default
                  is <span><strong class="command">warn</strong></span>.
                  For answers received from the network (<span><strong class="command">response</strong></span>)
                  the default is <span><strong class="command">ignore</strong></span>.
                </p>
<p>
                  The rules for legal hostnames and mail domains are derived
                  from RFC 952 and RFC 821 as modified by RFC 1123.
                </p>
<p><span><strong class="command">check-names</strong></span>
                  applies to the owner names of A, AAAA and MX records.
                  It also applies to the domain names in the RDATA of NS, SOA,
                  MX, and SRV records.
                  It also applies to the RDATA of PTR records where the owner
                  name indicated that it is a reverse lookup of a hostname
                  (the owner name ends in IN-ADDR.ARPA, IP6.ARPA, or IP6.INT).
                </p>
</dd>
<dt><span class="term"><span><strong class="command">check-dup-records</strong></span></span></dt>
<dd><p>
                  Check master zones for records that are treated as different
                  by DNSSEC but are semantically equal in plain DNS.  The
                  default is to <span><strong class="command">warn</strong></span>.  Other possible
                  values are <span><strong class="command">fail</strong></span> and
                  <span><strong class="command">ignore</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">check-mx</strong></span></span></dt>
<dd><p>
                  Check whether the MX record appears to refer to a IP address.
                  The default is to <span><strong class="command">warn</strong></span>.  Other possible
                  values are <span><strong class="command">fail</strong></span> and
                  <span><strong class="command">ignore</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">check-wildcard</strong></span></span></dt>
<dd><p>
                  This option is used to check for non-terminal wildcards.
                  The use of non-terminal wildcards is almost always as a
                  result of a failure
                  to understand the wildcard matching algorithm (RFC 1034).
                  This option
                  affects master zones.  The default (<span><strong class="command">yes</strong></span>) is to check
                  for non-terminal wildcards and issue a warning.
                </p></dd>
<dt><span class="term"><span><strong class="command">check-integrity</strong></span></span></dt>
<dd>
<p>
                  Perform post load zone integrity checks on master
                  zones.  This checks that MX and SRV records refer
                  to address (A or AAAA) records and that glue
                  address records exist for delegated zones.  For
                  MX and SRV records only in-zone hostnames are
                  checked (for out-of-zone hostnames use
                  <span><strong class="command">named-checkzone</strong></span>).
                  For NS records only names below top of zone are
                  checked (for out-of-zone names and glue consistency
                  checks use <span><strong class="command">named-checkzone</strong></span>).
                  The default is <span><strong class="command">yes</strong></span>.
                </p>
<p>
                  The use of the SPF record for publishing Sender
                  Policy Framework is deprecated as the migration
                  from using TXT records to SPF records was abandoned.
                  Enabling this option also checks that a TXT Sender
                  Policy Framework record exists (starts with "v=spf1")
                  if there is an SPF record. Warnings are emitted if the
                  TXT record does not exist and can be suppressed with
                  <span><strong class="command">check-spf</strong></span>.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">check-mx-cname</strong></span></span></dt>
<dd><p>
                  If <span><strong class="command">check-integrity</strong></span> is set then
                  fail, warn or ignore MX records that refer
                  to CNAMES.  The default is to <span><strong class="command">warn</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">check-srv-cname</strong></span></span></dt>
<dd><p>
                  If <span><strong class="command">check-integrity</strong></span> is set then
                  fail, warn or ignore SRV records that refer
                  to CNAMES.  The default is to <span><strong class="command">warn</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">check-sibling</strong></span></span></dt>
<dd><p>
                  When performing integrity checks, also check that
                  sibling glue exists.  The default is <span><strong class="command">yes</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">check-spf</strong></span></span></dt>
<dd><p>
                  If <span><strong class="command">check-integrity</strong></span> is set then
                  check that there is a TXT Sender Policy Framework
                  record present (starts with "v=spf1") if there is an
                  SPF record present. The default is
                  <span><strong class="command">warn</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">zero-no-soa-ttl</strong></span></span></dt>
<dd><p>
                  When returning authoritative negative responses to
                  SOA queries set the TTL of the SOA record returned in
                  the authority section to zero.
                  The default is <span><strong class="command">yes</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">zero-no-soa-ttl-cache</strong></span></span></dt>
<dd><p>
                  When caching a negative response to a SOA query
                  set the TTL to zero.
                  The default is <span><strong class="command">no</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">update-check-ksk</strong></span></span></dt>
<dd>
<p>
                  When set to the default value of <code class="literal">yes</code>,
                  check the KSK bit in each key to determine how the key
                  should be used when generating RRSIGs for a secure zone.
                </p>
<p>
                  Ordinarily, zone-signing keys (that is, keys without the
                  KSK bit set) are used to sign the entire zone, while
                  key-signing keys (keys with the KSK bit set) are only
                  used to sign the DNSKEY RRset at the zone apex.
                  However, if this option is set to <code class="literal">no</code>,
                  then the KSK bit is ignored; KSKs are treated as if they
                  were ZSKs and are used to sign the entire zone.  This is
                  similar to the <span><strong class="command">dnssec-signzone -z</strong></span>
                  command line option.
                </p>
<p>
                  When this option is set to <code class="literal">yes</code>, there
                  must be at least two active keys for every algorithm
                  represented in the DNSKEY RRset: at least one KSK and one
                  ZSK per algorithm.  If there is any algorithm for which
                  this requirement is not met, this option will be ignored
                  for that algorithm.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">dnssec-dnskey-kskonly</strong></span></span></dt>
<dd>
<p>
                  When this option and <span><strong class="command">update-check-ksk</strong></span>
                  are both set to <code class="literal">yes</code>, only key-signing
                  keys (that is, keys with the KSK bit set) will be used
                  to sign the DNSKEY RRset at the zone apex.  Zone-signing
                  keys (keys without the KSK bit set) will be used to sign
                  the remainder of the zone, but not the DNSKEY RRset.
                  This is similar to the
                  <span><strong class="command">dnssec-signzone -x</strong></span> command line option.
                </p>
<p>
                  The default is <span><strong class="command">no</strong></span>.  If
                  <span><strong class="command">update-check-ksk</strong></span> is set to
                  <code class="literal">no</code>, this option is ignored.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">dnssec-loadkeys-interval</strong></span></span></dt>
<dd><p>
                  When a zone is configured with <span><strong class="command">auto-dnssec
                  maintain;</strong></span> its key repository must be checked
                  periodically to see if any new keys have been added
                  or any existing keys' timing metadata has been updated
                  (see <a href="man.dnssec-keygen.html" title="dnssec-keygen"><span class="refentrytitle"><span class="application">dnssec-keygen</span></span>(8)</a> and
                  <a href="man.dnssec-settime.html" title="dnssec-settime"><span class="refentrytitle"><span class="application">dnssec-settime</span></span>(8)</a>).  The
                  <span><strong class="command">dnssec-loadkeys-interval</strong></span> option
                  sets the frequency of automatic repository checks, in
                  minutes.  The default is <code class="literal">60</code> (1 hour),
                  the minimum is <code class="literal">1</code> (1 minute), and the
                  maximum is <code class="literal">1440</code> (24 hours); any higher
                  value is silently reduced.
                </p></dd>
<dt><span class="term"><span><strong class="command">try-tcp-refresh</strong></span></span></dt>
<dd><p>
                  Try to refresh the zone using TCP if UDP queries fail.
                  For BIND 8 compatibility, the default is
                  <span><strong class="command">yes</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">dnssec-secure-to-insecure</strong></span></span></dt>
<dd>
<p>
                  Allow a dynamic zone to transition from secure to
                  insecure (i.e., signed to unsigned) by deleting all
                  of the DNSKEY records.  The default is <span><strong class="command">no</strong></span>.
                  If set to <span><strong class="command">yes</strong></span>, and if the DNSKEY RRset
                  at the zone apex is deleted, all RRSIG and NSEC records
                  will be removed from the zone as well.
                </p>
<p>
                  If the zone uses NSEC3, then it is also necessary to
                  delete the NSEC3PARAM RRset from the zone apex; this will
                  cause the removal of all corresponding NSEC3 records.
                  (It is expected that this requirement will be eliminated
                  in a future release.)
                </p>
<p>
                  Note that if a zone has been configured with
                  <span><strong class="command">auto-dnssec maintain</strong></span> and the
                  private keys remain accessible in the key repository,
                  then the zone will be automatically signed again the
                  next time <span><strong class="command">named</strong></span> is started.
                </p>
</dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2583443"></a>Forwarding</h4></div></div></div>
<p>
            The forwarding facility can be used to create a large site-wide
            cache on a few servers, reducing traffic over links to external
            name servers. It can also be used to allow queries by servers that
            do not have direct access to the Internet, but wish to look up
            exterior
            names anyway. Forwarding occurs only on those queries for which
            the server is not authoritative and does not have the answer in
            its cache.
          </p>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">forward</strong></span></span></dt>
<dd><p>
                  This option is only meaningful if the
                  forwarders list is not empty. A value of <code class="varname">first</code>,
                  the default, causes the server to query the forwarders
                  first &#8212; and
                  if that doesn't answer the question, the server will then
                  look for
                  the answer itself. If <code class="varname">only</code> is
                  specified, the
                  server will only query the forwarders.
                </p></dd>
<dt><span class="term"><span><strong class="command">forwarders</strong></span></span></dt>
<dd><p>
                  Specifies the IP addresses to be used
                  for forwarding. The default is the empty list (no
                  forwarding).
                </p></dd>
</dl></div>
<p>
            Forwarding can also be configured on a per-domain basis, allowing
            for the global forwarding options to be overridden in a variety
            of ways. You can set particular domains to use different
            forwarders,
            or have a different <span><strong class="command">forward only/first</strong></span> behavior,
            or not forward at all, see <a href="Bv9ARM.ch06.html#zone_statement_grammar" title="zone
            Statement Grammar">the section called &#8220;<span><strong class="command">zone</strong></span>
            Statement Grammar&#8221;</a>.
          </p>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2583570"></a>Dual-stack Servers</h4></div></div></div>
<p>
            Dual-stack servers are used as servers of last resort to work
            around
            problems in reachability due the lack of support for either IPv4
            or IPv6
            on the host machine.
          </p>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">dual-stack-servers</strong></span></span></dt>
<dd><p>
                  Specifies host names or addresses of machines with access to
                  both IPv4 and IPv6 transports. If a hostname is used, the
                  server must be able
                  to resolve the name using only the transport it has.  If the
                  machine is dual
                  stacked, then the <span><strong class="command">dual-stack-servers</strong></span> have no effect unless
                  access to a transport has been disabled on the command line
                  (e.g. <span><strong class="command">named -4</strong></span>).
                </p></dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="access_control"></a>Access Control</h4></div></div></div>
<p>
            Access to the server can be restricted based on the IP address
            of the requesting system. See <a href="Bv9ARM.ch06.html#address_match_lists" title="Address Match Lists">the section called &#8220;Address Match Lists&#8221;</a> for
            details on how to specify IP address lists.
          </p>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">allow-notify</strong></span></span></dt>
<dd><p>
                  Specifies which hosts are allowed to
                  notify this server, a slave, of zone changes in addition
                  to the zone masters.
                  <span><strong class="command">allow-notify</strong></span> may also be
                  specified in the
                  <span><strong class="command">zone</strong></span> statement, in which case
                  it overrides the
                  <span><strong class="command">options allow-notify</strong></span>
                  statement.  It is only meaningful
                  for a slave zone.  If not specified, the default is to
                  process notify messages
                  only from a zone's master.
                </p></dd>
<dt><span class="term"><span><strong class="command">allow-query</strong></span></span></dt>
<dd>
<p>
                  Specifies which hosts are allowed to ask ordinary
                  DNS questions. <span><strong class="command">allow-query</strong></span> may
                  also be specified in the <span><strong class="command">zone</strong></span>
                  statement, in which case it overrides the
                  <span><strong class="command">options allow-query</strong></span> statement.
                  If not specified, the default is to allow queries
                  from all hosts.
                </p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
                    <span><strong class="command">allow-query-cache</strong></span> is now
                    used to specify access to the cache.
                  </p>
</div>
</dd>
<dt><span class="term"><span><strong class="command">allow-query-on</strong></span></span></dt>
<dd>
<p>
                  Specifies which local addresses can accept ordinary
                  DNS questions. This makes it possible, for instance,
                  to allow queries on internal-facing interfaces but
                  disallow them on external-facing ones, without
                  necessarily knowing the internal network's addresses.
                </p>
<p>
                  Note that <span><strong class="command">allow-query-on</strong></span> is only
                  checked for queries that are permitted by
                  <span><strong class="command">allow-query</strong></span>.  A query must be
                  allowed by both ACLs, or it will be refused.
                </p>
<p>
                  <span><strong class="command">allow-query-on</strong></span> may
                  also be specified in the <span><strong class="command">zone</strong></span>
                  statement, in which case it overrides the
                  <span><strong class="command">options allow-query-on</strong></span> statement.
                </p>
<p>
                  If not specified, the default is to allow queries
                  on all addresses.
                </p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
                    <span><strong class="command">allow-query-cache</strong></span> is
                    used to specify access to the cache.
                  </p>
</div>
</dd>
<dt><span class="term"><span><strong class="command">allow-query-cache</strong></span></span></dt>
<dd><p>
                  Specifies which hosts are allowed to get answers
                  from the cache.  If <span><strong class="command">allow-query-cache</strong></span>
                  is not set then <span><strong class="command">allow-recursion</strong></span>
                  is used if set, otherwise <span><strong class="command">allow-query</strong></span>
                  is used if set unless <span><strong class="command">recursion no;</strong></span> is
                  set in which case <span><strong class="command">none;</strong></span> is used,
                  otherwise the default (<span><strong class="command">localnets;</strong></span>
                  <span><strong class="command">localhost;</strong></span>) is used.
                </p></dd>
<dt><span class="term"><span><strong class="command">allow-query-cache-on</strong></span></span></dt>
<dd><p>
                  Specifies which local addresses can give answers
                  from the cache.  If not specified, the default is
                  to allow cache queries on any address,
                  <span><strong class="command">localnets</strong></span> and
                  <span><strong class="command">localhost</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">allow-recursion</strong></span></span></dt>
<dd><p>
                  Specifies which hosts are allowed to make recursive
                  queries through this server. If
                  <span><strong class="command">allow-recursion</strong></span> is not set
                  then <span><strong class="command">allow-query-cache</strong></span> is
                  used if set, otherwise <span><strong class="command">allow-query</strong></span>
                  is used if set, otherwise the default
                  (<span><strong class="command">localnets;</strong></span>
                  <span><strong class="command">localhost;</strong></span>) is used.
                </p></dd>
<dt><span class="term"><span><strong class="command">allow-recursion-on</strong></span></span></dt>
<dd><p>
                  Specifies which local addresses can accept recursive
                  queries.  If not specified, the default is to allow
                  recursive queries on all addresses.
                </p></dd>
<dt><span class="term"><span><strong class="command">allow-update</strong></span></span></dt>
<dd><p>
                  Specifies which hosts are allowed to
                  submit Dynamic DNS updates for master zones. The default is
                  to deny
                  updates from all hosts.  Note that allowing updates based
                  on the requestor's IP address is insecure; see
                  <a href="Bv9ARM.ch07.html#dynamic_update_security" title="Dynamic Update Security">the section called &#8220;Dynamic Update Security&#8221;</a> for details.
                </p></dd>
<dt><span class="term"><span><strong class="command">allow-update-forwarding</strong></span></span></dt>
<dd>
<p>
                  Specifies which hosts are allowed to
                  submit Dynamic DNS updates to slave zones to be forwarded to
                  the
                  master.  The default is <strong class="userinput"><code>{ none; }</code></strong>,
                  which
                  means that no update forwarding will be performed.  To
                  enable
                  update forwarding, specify
                  <strong class="userinput"><code>allow-update-forwarding { any; };</code></strong>.
                  Specifying values other than <strong class="userinput"><code>{ none; }</code></strong> or
                  <strong class="userinput"><code>{ any; }</code></strong> is usually
                  counterproductive, since
                  the responsibility for update access control should rest
                  with the
                  master server, not the slaves.
                </p>
<p>
                  Note that enabling the update forwarding feature on a slave
                  server
                  may expose master servers relying on insecure IP address
                  based
                  access control to attacks; see <a href="Bv9ARM.ch07.html#dynamic_update_security" title="Dynamic Update Security">the section called &#8220;Dynamic Update Security&#8221;</a>
                  for more details.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">allow-v6-synthesis</strong></span></span></dt>
<dd><p>
                  This option was introduced for the smooth transition from
                  AAAA
                  to A6 and from "nibble labels" to binary labels.
                  However, since both A6 and binary labels were then
                  deprecated,
                  this option was also deprecated.
                  It is now ignored with some warning messages.
                </p></dd>
<dt><span class="term"><span><strong class="command">allow-transfer</strong></span></span></dt>
<dd><p>
                  Specifies which hosts are allowed to
                  receive zone transfers from the server. <span><strong class="command">allow-transfer</strong></span> may
                  also be specified in the <span><strong class="command">zone</strong></span>
                  statement, in which
                  case it overrides the <span><strong class="command">options allow-transfer</strong></span> statement.
                  If not specified, the default is to allow transfers to all
                  hosts.
                </p></dd>
<dt><span class="term"><span><strong class="command">blackhole</strong></span></span></dt>
<dd><p>
                  Specifies a list of addresses that the
                  server will not accept queries from or use to resolve a
                  query. Queries
                  from these addresses will not be responded to. The default
                  is <strong class="userinput"><code>none</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">filter-aaaa</strong></span></span></dt>
<dd><p>
                  Specifies a list of addresses to which
                  <span><strong class="command">filter-aaaa-on-v4</strong></span>
                  is applies.  The default is <strong class="userinput"><code>any</code></strong>.
                </p></dd>
<dt><span class="term"><span><strong class="command">no-case-compress</strong></span></span></dt>
<dd>
<p>
                  Specifies a list of addresses which require responses
                  to use case-insensitive compression.  This ACL can be
                  used when <span><strong class="command">named</strong></span> needs to work with
                  clients that do not comply with the requirement in RFC
                  1034 to use case-insensitive name comparisons when
                  checking for matching domain names.
                </p>
<p>
                  If left undefined, the ACL defaults to
                  <span><strong class="command">none</strong></span>: case-insensitive compression
                  will be used for all clients.  If the ACL is defined and
                  matches a client, then case will be ignored when
                  compressing domain names in DNS responses sent to that
                  client.
                </p>
<p>
                  This can result in slightly smaller responses: if
                  a response contains the names "example.com" and
                  "example.COM", case-insensitive compression would treat
                  the second one as a duplicate.  It also ensures
                  that the case of the query name exactly matches the
                  case of the owner names of returned records, rather
                  than matching the case of the records entered in
                  the zone file.  This allows responses to exactly
                  match the query, which is required by some clients
                  due to incorrect use of case-sensitive comparisons.
                </p>
<p>
                  Case-insensitive compression is <span class="emphasis"><em>always</em></span>
                  used in AXFR and IXFR responses, regardless of whether
                  the client matches this ACL.
                </p>
<p>
                  There are circumstances in which <span><strong class="command">named</strong></span>
                  will not preserve the case of owner names of records:
                  if a zone file defines records of different types with
                  the same name, but the capitalization of the name is
                  different (e.g., "www.example.com/A" and
                  "WWW.EXAMPLE.COM/AAAA"), then all responses for that
                  name will use the <span class="emphasis"><em>first</em></span> version
                  of the name that was used in the zone file.  This
                  limitation may be addressed in a future release.  However,
                  domain names specified in the rdata of resource records
                  (i.e., records of type NS, MX, CNAME, etc) will always
                  have their case preserved unless the client matches this
                  ACL.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">resolver-query-timeout</strong></span></span></dt>
<dd><p>
                  The amount of time the resolver will spend attempting
                  to resolve a recursive query before failing.  The default
                  and minimum is <code class="literal">10</code> and the maximum is
                  <code class="literal">30</code>.  Setting it to <code class="literal">0</code>
                  will result in the default being used.
                </p></dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2584312"></a>Interfaces</h4></div></div></div>
<p>
            The interfaces and ports that the server will answer queries
            from may be specified using the <span><strong class="command">listen-on</strong></span> option. <span><strong class="command">listen-on</strong></span> takes
            an optional port and an <code class="varname">address_match_list</code>
            of IPv4 addresses.  (IPv6 addresses are ignored, with a
            logged warning.)
            The server will listen on all interfaces allowed by the address
            match list. If a port is not specified, port 53 will be used.
          </p>
<p>
            Multiple <span><strong class="command">listen-on</strong></span> statements are
            allowed.
            For example,
          </p>
<pre class="programlisting">listen-on { 5.6.7.8; };
listen-on port 1234 { !1.2.3.4; 1.2/16; };
</pre>
<p>
            will enable the name server on port 53 for the IP address
            5.6.7.8, and on port 1234 of an address on the machine in net
            1.2 that is not 1.2.3.4.
          </p>
<p>
            If no <span><strong class="command">listen-on</strong></span> is specified, the
            server will listen on port 53 on all IPv4 interfaces.
          </p>
<p>
            The <span><strong class="command">listen-on-v6</strong></span> option is used to
            specify the interfaces and the ports on which the server will
            listen
            for incoming queries sent using IPv6.
          </p>
<p>
            When </p>
<pre class="programlisting">{ any; }</pre>
<p> is
            specified
            as the <code class="varname">address_match_list</code> for the
            <span><strong class="command">listen-on-v6</strong></span> option,
            the server does not bind a separate socket to each IPv6 interface
            address as it does for IPv4 if the operating system has enough API
            support for IPv6 (specifically if it conforms to RFC 3493 and RFC
            3542).
            Instead, it listens on the IPv6 wildcard address.
            If the system only has incomplete API support for IPv6, however,
            the behavior is the same as that for IPv4.
          </p>
<p>
            A list of particular IPv6 addresses can also be specified, in
            which case
            the server listens on a separate socket for each specified
            address,
            regardless of whether the desired API is supported by the system.
            IPv4 addresses specified in <span><strong class="command">listen-on-v6</strong></span>
            will be ignored, with a logged warning.
          </p>
<p>
            Multiple <span><strong class="command">listen-on-v6</strong></span> options can
            be used.
            For example,
          </p>
<pre class="programlisting">listen-on-v6 { any; };
listen-on-v6 port 1234 { !2001:db8::/32; any; };
</pre>
<p>
            will enable the name server on port 53 for any IPv6 addresses
            (with a single wildcard socket),
            and on port 1234 of IPv6 addresses that is not in the prefix
            2001:db8::/32 (with separate sockets for each matched address.)
          </p>
<p>
            To make the server not listen on any IPv6 address, use
          </p>
<pre class="programlisting">listen-on-v6 { none; };
</pre>
<p>
            If no <span><strong class="command">listen-on-v6</strong></span> option is
            specified, the server will not listen on any IPv6 address
            unless <span><strong class="command">-6</strong></span> is specified when <span><strong class="command">named</strong></span> is
            invoked.  If <span><strong class="command">-6</strong></span> is specified then
            <span><strong class="command">named</strong></span> will listen on port 53 on all IPv6 interfaces by default.
          </p>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="query_address"></a>Query Address</h4></div></div></div>
<p>
            If the server doesn't know the answer to a question, it will
            query other name servers. <span><strong class="command">query-source</strong></span> specifies
            the address and port used for such queries. For queries sent over
            IPv6, there is a separate <span><strong class="command">query-source-v6</strong></span> option.
            If <span><strong class="command">address</strong></span> is <span><strong class="command">*</strong></span> (asterisk) or is omitted,
            a wildcard IP address (<span><strong class="command">INADDR_ANY</strong></span>)
            will be used.
          </p>
<p>
            If <span><strong class="command">port</strong></span> is <span><strong class="command">*</strong></span> or is omitted,
            a random port number from a pre-configured
            range is picked up and will be used for each query.
            The port range(s) is that specified in
            the <span><strong class="command">use-v4-udp-ports</strong></span> (for IPv4)
            and <span><strong class="command">use-v6-udp-ports</strong></span> (for IPv6)
            options, excluding the ranges specified in
            the <span><strong class="command">avoid-v4-udp-ports</strong></span>
            and <span><strong class="command">avoid-v6-udp-ports</strong></span> options, respectively.
          </p>
<p>
            The defaults of the <span><strong class="command">query-source</strong></span> and
            <span><strong class="command">query-source-v6</strong></span> options
            are:
          </p>
<pre class="programlisting">query-source address * port *;
query-source-v6 address * port *;
</pre>
<p>
            If <span><strong class="command">use-v4-udp-ports</strong></span> or
            <span><strong class="command">use-v6-udp-ports</strong></span> is unspecified,
            <span><strong class="command">named</strong></span> will check if the operating
            system provides a programming interface to retrieve the
            system's default range for ephemeral ports.
            If such an interface is available,
            <span><strong class="command">named</strong></span> will use the corresponding system
            default range; otherwise, it will use its own defaults:
         </p>
<pre class="programlisting">use-v4-udp-ports { range 1024 65535; };
use-v6-udp-ports { range 1024 65535; };
</pre>
<p>
            Note: make sure the ranges be sufficiently large for
            security.  A desirable size depends on various parameters,
            but we generally recommend it contain at least 16384 ports
            (14 bits of entropy).
            Note also that the system's default range when used may be
            too small for this purpose, and that the range may even be
            changed while <span><strong class="command">named</strong></span> is running; the new
            range will automatically be applied when <span><strong class="command">named</strong></span>
            is reloaded.
            It is encouraged to
            configure <span><strong class="command">use-v4-udp-ports</strong></span> and
            <span><strong class="command">use-v6-udp-ports</strong></span> explicitly so that the
            ranges are sufficiently large and are reasonably
            independent from the ranges used by other applications.
          </p>
<p>
            Note: the operational configuration
            where <span><strong class="command">named</strong></span> runs may prohibit the use
            of some ports.  For example, UNIX systems will not allow
            <span><strong class="command">named</strong></span> running without a root privilege
            to use ports less than 1024.
            If such ports are included in the specified (or detected)
            set of query ports, the corresponding query attempts will
            fail, resulting in resolution failures or delay.
            It is therefore important to configure the set of ports
            that can be safely used in the expected operational environment.
          </p>
<p>
            The defaults of the <span><strong class="command">avoid-v4-udp-ports</strong></span> and
            <span><strong class="command">avoid-v6-udp-ports</strong></span> options
            are:
          </p>
<pre class="programlisting">avoid-v4-udp-ports {};
avoid-v6-udp-ports {};
</pre>
<p>
            Note: BIND 9.5.0 introduced
            the <span><strong class="command">use-queryport-pool</strong></span> 
            option to support a pool of such random ports, but this
            option is now obsolete because reusing the same ports in
            the pool may not be sufficiently secure.
            For the same reason, it is generally strongly discouraged to
            specify a particular port for the
            <span><strong class="command">query-source</strong></span> or
            <span><strong class="command">query-source-v6</strong></span> options;
            it implicitly disables the use of randomized port numbers.
          </p>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">use-queryport-pool</strong></span></span></dt>
<dd><p>
                  This option is obsolete.
                </p></dd>
<dt><span class="term"><span><strong class="command">queryport-pool-ports</strong></span></span></dt>
<dd><p>
                  This option is obsolete.
                </p></dd>
<dt><span class="term"><span><strong class="command">queryport-pool-updateinterval</strong></span></span></dt>
<dd><p>
                  This option is obsolete.
                </p></dd>
</dl></div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
              The address specified in the <span><strong class="command">query-source</strong></span> option
              is used for both UDP and TCP queries, but the port applies only
              to UDP queries.  TCP queries always use a random
              unprivileged port.
            </p>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
              Solaris 2.5.1 and earlier does not support setting the source
              address for TCP sockets.
            </p>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
              See also <span><strong class="command">transfer-source</strong></span> and
              <span><strong class="command">notify-source</strong></span>.
            </p>
</div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="zone_transfers"></a>Zone Transfers</h4></div></div></div>
<p>
            <acronym class="acronym">BIND</acronym> has mechanisms in place to
            facilitate zone transfers
            and set limits on the amount of load that transfers place on the
            system. The following options apply to zone transfers.
          </p>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">also-notify</strong></span></span></dt>
<dd>
<p>
                  Defines a global list of IP addresses of name servers
                  that are also sent NOTIFY messages whenever a fresh copy of
                  the
                  zone is loaded, in addition to the servers listed in the
                  zone's NS records.
                  This helps to ensure that copies of the zones will
                  quickly converge on stealth servers.
                  Optionally, a port may be specified with each
                  <span><strong class="command">also-notify</strong></span> address to send
                  the notify messages to a port other than the
                  default of 53.
                  An optional TSIG key can also be specified with each
                  address to cause the notify messages to be signed; this
                  can be useful when sending notifies to multiple views.
                  In place of explicit addresses, one or more named
                  <span><strong class="command">masters</strong></span> lists can be used.
                </p>
<p>
                  If an <span><strong class="command">also-notify</strong></span> list
                  is given in a <span><strong class="command">zone</strong></span> statement,
                  it will override
                  the <span><strong class="command">options also-notify</strong></span>
                  statement. When a <span><strong class="command">zone notify</strong></span>
                  statement
                  is set to <span><strong class="command">no</strong></span>, the IP
                  addresses in the global <span><strong class="command">also-notify</strong></span> list will
                  not be sent NOTIFY messages for that zone. The default is
                  the empty
                  list (no global notification list).
                </p>
</dd>
<dt><span class="term"><span><strong class="command">max-transfer-time-in</strong></span></span></dt>
<dd><p>
                  Inbound zone transfers running longer than
                  this many minutes will be terminated. The default is 120
                  minutes
                  (2 hours).  The maximum value is 28 days (40320 minutes).
                </p></dd>
<dt><span class="term"><span><strong class="command">max-transfer-idle-in</strong></span></span></dt>
<dd><p>
                  Inbound zone transfers making no progress
                  in this many minutes will be terminated. The default is 60
                  minutes
                  (1 hour).  The maximum value is 28 days (40320 minutes).
                </p></dd>
<dt><span class="term"><span><strong class="command">max-transfer-time-out</strong></span></span></dt>
<dd><p>
                  Outbound zone transfers running longer than
                  this many minutes will be terminated. The default is 120
                  minutes
                  (2 hours).  The maximum value is 28 days (40320 minutes).
                </p></dd>
<dt><span class="term"><span><strong class="command">max-transfer-idle-out</strong></span></span></dt>
<dd><p>
                  Outbound zone transfers making no progress
                  in this many minutes will be terminated.  The default is 60
                  minutes (1
                  hour).  The maximum value is 28 days (40320 minutes).
                </p></dd>
<dt><span class="term"><span><strong class="command">serial-query-rate</strong></span></span></dt>
<dd>
<p>
                  Slave servers will periodically query master
                  servers to find out if zone serial numbers have
                  changed. Each such query uses a minute amount of
                  the slave server's network bandwidth.  To limit
                  the amount of bandwidth used, BIND 9 limits the
                  rate at which queries are sent.  The value of the
                  <span><strong class="command">serial-query-rate</strong></span> option, an
                  integer, is the maximum number of queries sent
                  per second.  The default is 20 per second.
                  The lowest possible rate is one per second; when set
                  to zero, it will be silently raised to one.
                </p>
<p>
                  In addition to controlling the rate SOA refresh
                  queries are issued at
                  <span><strong class="command">serial-query-rate</strong></span> also controls
                  the rate at which NOTIFY messages are sent from
                  both master and slave zones.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">serial-queries</strong></span></span></dt>
<dd><p>
                  In BIND 8, the <span><strong class="command">serial-queries</strong></span>
                  option
                  set the maximum number of concurrent serial number queries
                  allowed to be outstanding at any given time.
                  BIND 9 does not limit the number of outstanding
                  serial queries and ignores the <span><strong class="command">serial-queries</strong></span> option.
                  Instead, it limits the rate at which the queries are sent
                  as defined using the <span><strong class="command">serial-query-rate</strong></span> option.
                </p></dd>
<dt><span class="term"><span><strong class="command">transfer-format</strong></span></span></dt>
<dd><p>
                  Zone transfers can be sent using two different formats,
                  <span><strong class="command">one-answer</strong></span> and
                  <span><strong class="command">many-answers</strong></span>.
                  The <span><strong class="command">transfer-format</strong></span> option is used
                  on the master server to determine which format it sends.
                  <span><strong class="command">one-answer</strong></span> uses one DNS message per
                  resource record transferred.
                  <span><strong class="command">many-answers</strong></span> packs as many resource
                  records as possible into a message.
                  <span><strong class="command">many-answers</strong></span> is more efficient, but is
                  only supported by relatively new slave servers,
                  such as <acronym class="acronym">BIND</acronym> 9, <acronym class="acronym">BIND</acronym>
                  8.x and <acronym class="acronym">BIND</acronym> 4.9.5 onwards.
                  The <span><strong class="command">many-answers</strong></span> format is also supported by
                  recent Microsoft Windows nameservers.
                  The default is <span><strong class="command">many-answers</strong></span>.
                  <span><strong class="command">transfer-format</strong></span> may be overridden on a
                  per-server basis by using the <span><strong class="command">server</strong></span>
                  statement.
                </p></dd>
<dt><span class="term"><span><strong class="command">transfers-in</strong></span></span></dt>
<dd><p>
                  The maximum number of inbound zone transfers
                  that can be running concurrently. The default value is <code class="literal">10</code>.
                  Increasing <span><strong class="command">transfers-in</strong></span> may
                  speed up the convergence
                  of slave zones, but it also may increase the load on the
                  local system.
                </p></dd>
<dt><span class="term"><span><strong class="command">transfers-out</strong></span></span></dt>
<dd><p>
                  The maximum number of outbound zone transfers
                  that can be running concurrently. Zone transfer requests in
                  excess
                  of the limit will be refused. The default value is <code class="literal">10</code>.
                </p></dd>
<dt><span class="term"><span><strong class="command">transfers-per-ns</strong></span></span></dt>
<dd><p>
                  The maximum number of inbound zone transfers
                  that can be concurrently transferring from a given remote
                  name server.
                  The default value is <code class="literal">2</code>.
                  Increasing <span><strong class="command">transfers-per-ns</strong></span>
                  may
                  speed up the convergence of slave zones, but it also may
                  increase
                  the load on the remote name server. <span><strong class="command">transfers-per-ns</strong></span> may
                  be overridden on a per-server basis by using the <span><strong class="command">transfers</strong></span> phrase
                  of the <span><strong class="command">server</strong></span> statement.
                </p></dd>
<dt><span class="term"><span><strong class="command">transfer-source</strong></span></span></dt>
<dd>
<p><span><strong class="command">transfer-source</strong></span>
                  determines which local address will be bound to IPv4
                  TCP connections used to fetch zones transferred
                  inbound by the server.  It also determines the
                  source IPv4 address, and optionally the UDP port,
                  used for the refresh queries and forwarded dynamic
                  updates.  If not set, it defaults to a system
                  controlled value which will usually be the address
                  of the interface "closest to" the remote end. This
                  address must appear in the remote end's
                  <span><strong class="command">allow-transfer</strong></span> option for the
                  zone being transferred, if one is specified. This
                  statement sets the
                  <span><strong class="command">transfer-source</strong></span> for all zones,
                  but can be overridden on a per-view or per-zone
                  basis by including a
                  <span><strong class="command">transfer-source</strong></span> statement within
                  the <span><strong class="command">view</strong></span> or
                  <span><strong class="command">zone</strong></span> block in the configuration
                  file.
                </p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
                    Solaris 2.5.1 and earlier does not support setting the
                    source address for TCP sockets.
                  </p>
</div>
</dd>
<dt><span class="term"><span><strong class="command">transfer-source-v6</strong></span></span></dt>
<dd><p>
                  The same as <span><strong class="command">transfer-source</strong></span>,
                  except zone transfers are performed using IPv6.
                </p></dd>
<dt><span class="term"><span><strong class="command">alt-transfer-source</strong></span></span></dt>
<dd>
<p>
                  An alternate transfer source if the one listed in
                  <span><strong class="command">transfer-source</strong></span> fails and
                  <span><strong class="command">use-alt-transfer-source</strong></span> is
                  set.
                </p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
                  If you do not wish the alternate transfer source
                  to be used, you should set
                  <span><strong class="command">use-alt-transfer-source</strong></span>
                  appropriately and you should not depend upon
                  getting an answer back to the first refresh
                  query.
                </div>
</dd>
<dt><span class="term"><span><strong class="command">alt-transfer-source-v6</strong></span></span></dt>
<dd><p>
                  An alternate transfer source if the one listed in
                  <span><strong class="command">transfer-source-v6</strong></span> fails and
                  <span><strong class="command">use-alt-transfer-source</strong></span> is
                  set.
                </p></dd>
<dt><span class="term"><span><strong class="command">use-alt-transfer-source</strong></span></span></dt>
<dd><p>
                  Use the alternate transfer sources or not.  If views are
                  specified this defaults to <span><strong class="command">no</strong></span>
                  otherwise it defaults to
                  <span><strong class="command">yes</strong></span> (for BIND 8
                  compatibility).
                </p></dd>
<dt><span class="term"><span><strong class="command">notify-source</strong></span></span></dt>
<dd>
<p><span><strong class="command">notify-source</strong></span>
                  determines which local source address, and
                  optionally UDP port, will be used to send NOTIFY
                  messages.  This address must appear in the slave
                  server's <span><strong class="command">masters</strong></span> zone clause or
                  in an <span><strong class="command">allow-notify</strong></span> clause.  This
                  statement sets the <span><strong class="command">notify-source</strong></span>
                  for all zones, but can be overridden on a per-zone or
                  per-view basis by including a
                  <span><strong class="command">notify-source</strong></span> statement within
                  the <span><strong class="command">zone</strong></span> or
                  <span><strong class="command">view</strong></span> block in the configuration
                  file.
                </p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
                    Solaris 2.5.1 and earlier does not support setting the
                    source address for TCP sockets.
                  </p>
</div>
</dd>
<dt><span class="term"><span><strong class="command">notify-source-v6</strong></span></span></dt>
<dd><p>
                  Like <span><strong class="command">notify-source</strong></span>,
                  but applies to notify messages sent to IPv6 addresses.
                </p></dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2585465"></a>UDP Port Lists</h4></div></div></div>
<p>
            <span><strong class="command">use-v4-udp-ports</strong></span>,
            <span><strong class="command">avoid-v4-udp-ports</strong></span>,
            <span><strong class="command">use-v6-udp-ports</strong></span>, and
            <span><strong class="command">avoid-v6-udp-ports</strong></span>
            specify a list of IPv4 and IPv6 UDP ports that will be
            used or not used as source ports for UDP messages.
            See <a href="Bv9ARM.ch06.html#query_address" title="Query Address">the section called &#8220;Query Address&#8221;</a> about how the
            available ports are determined.
            For example, with the following configuration
          </p>
<pre class="programlisting">
use-v6-udp-ports { range 32768 65535; };
avoid-v6-udp-ports { 40000; range 50000 60000; };
</pre>
<p>
             UDP ports of IPv6 messages sent
             from <span><strong class="command">named</strong></span> will be in one
             of the following ranges: 32768 to 39999, 40001 to 49999,
             and 60001 to 65535.
           </p>
<p>
             <span><strong class="command">avoid-v4-udp-ports</strong></span> and
             <span><strong class="command">avoid-v6-udp-ports</strong></span> can be used
             to prevent <span><strong class="command">named</strong></span> from choosing as its random source port a
             port that is blocked by your firewall or a port that is
             used by other applications;
             if a query went out with a source port blocked by a
             firewall, the
             answer would not get by the firewall and the name server would
             have to query again.
             Note: the desired range can also be represented only with
             <span><strong class="command">use-v4-udp-ports</strong></span> and
             <span><strong class="command">use-v6-udp-ports</strong></span>, and the
             <span><strong class="command">avoid-</strong></span> options are redundant in that
             sense; they are provided for backward compatibility and
             to possibly simplify the port specification.
           </p>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2585525"></a>Operating System Resource Limits</h4></div></div></div>
<p>
            The server's usage of many system resources can be limited.
            Scaled values are allowed when specifying resource limits.  For
            example, <span><strong class="command">1G</strong></span> can be used instead of
            <span><strong class="command">1073741824</strong></span> to specify a limit of
            one
            gigabyte. <span><strong class="command">unlimited</strong></span> requests
            unlimited use, or the
            maximum available amount. <span><strong class="command">default</strong></span>
            uses the limit
            that was in force when the server was started. See the description
            of <span><strong class="command">size_spec</strong></span> in <a href="Bv9ARM.ch06.html#configuration_file_elements" title="Configuration File Elements">the section called &#8220;Configuration File Elements&#8221;</a>.
          </p>
<p>
            The following options set operating system resource limits for
            the name server process.  Some operating systems don't support
            some or
            any of the limits. On such systems, a warning will be issued if
            the
            unsupported limit is used.
          </p>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">coresize</strong></span></span></dt>
<dd><p>
                  The maximum size of a core dump. The default
                  is <code class="literal">default</code>.
                </p></dd>
<dt><span class="term"><span><strong class="command">datasize</strong></span></span></dt>
<dd><p>
                  The maximum amount of data memory the server
                  may use. The default is <code class="literal">default</code>.
                  This is a hard limit on server memory usage.
                  If the server attempts to allocate memory in excess of this
                  limit, the allocation will fail, which may in turn leave
                  the server unable to perform DNS service.  Therefore,
                  this option is rarely useful as a way of limiting the
                  amount of memory used by the server, but it can be used
                  to raise an operating system data size limit that is
                  too small by default.  If you wish to limit the amount
                  of memory used by the server, use the
                  <span><strong class="command">max-cache-size</strong></span> and
                  <span><strong class="command">recursive-clients</strong></span>
                  options instead.
                </p></dd>
<dt><span class="term"><span><strong class="command">files</strong></span></span></dt>
<dd><p>
                  The maximum number of files the server
                  may have open concurrently. The default is <code class="literal">unlimited</code>.
                </p></dd>
<dt><span class="term"><span><strong class="command">stacksize</strong></span></span></dt>
<dd><p>
                  The maximum amount of stack memory the server
                  may use. The default is <code class="literal">default</code>.
                </p></dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="server_resource_limits"></a>Server  Resource Limits</h4></div></div></div>
<p>
            The following options set limits on the server's
            resource consumption that are enforced internally by the
            server rather than the operating system.
          </p>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">max-ixfr-log-size</strong></span></span></dt>
<dd><p>
                  This option is obsolete; it is accepted
                  and ignored for BIND 8 compatibility.  The option
                  <span><strong class="command">max-journal-size</strong></span> performs a
                  similar function in BIND 9.
                </p></dd>
<dt><span class="term"><span><strong class="command">max-journal-size</strong></span></span></dt>
<dd><p>
                  Sets a maximum size for each journal file
                  (see <a href="Bv9ARM.ch04.html#journal" title="The journal file">the section called &#8220;The journal file&#8221;</a>).  When the journal file
                  approaches
                  the specified size, some of the oldest transactions in the
                  journal
                  will be automatically removed.  The largest permitted
                  value is 2 gigabytes. The default is
                  <code class="literal">unlimited</code>, which also
                  means 2 gigabytes.
                  This may also be set on a per-zone basis.
                </p></dd>
<dt><span class="term"><span><strong class="command">host-statistics-max</strong></span></span></dt>
<dd><p>
                  In BIND 8, specifies the maximum number of host statistics
                  entries to be kept.
                  Not implemented in BIND 9.
                </p></dd>
<dt><span class="term"><span><strong class="command">recursive-clients</strong></span></span></dt>
<dd><p>
                  The maximum number of simultaneous recursive lookups
                  the server will perform on behalf of clients.  The default
                  is
                  <code class="literal">1000</code>.  Because each recursing
                  client uses a fair
                  bit of memory, on the order of 20 kilobytes, the value of
                  the
                  <span><strong class="command">recursive-clients</strong></span> option may
                  have to be decreased
                  on hosts with limited memory.
                </p></dd>
<dt><span class="term"><span><strong class="command">tcp-clients</strong></span></span></dt>
<dd><p>
                  The maximum number of simultaneous client TCP
                  connections that the server will accept.
                  The default is <code class="literal">100</code>.
                </p></dd>
<dt><span class="term"><span><strong class="command">reserved-sockets</strong></span></span></dt>
<dd>
<p>
                  The number of file descriptors reserved for TCP, stdio,
                  etc.  This needs to be big enough to cover the number of
                  interfaces <span><strong class="command">named</strong></span> listens on, <span><strong class="command">tcp-clients</strong></span> as well as
                  to provide room for outgoing TCP queries and incoming zone
                  transfers.  The default is <code class="literal">512</code>.
                  The minimum value is <code class="literal">128</code> and the
                  maximum value is <code class="literal">128</code> less than
                  maxsockets (-S).  This option may be removed in the future.
                </p>
<p>
                  This option has little effect on Windows.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">max-cache-size</strong></span></span></dt>
<dd><p>
                  The maximum amount of memory to use for the
                  server's cache, in bytes.
                  When the amount of data in the cache
                  reaches this limit, the server will cause records to expire
                  prematurely based on an LRU based strategy so that
                  the limit is not exceeded.
                  A value of 0 is special, meaning that
                  records are purged from the cache only when their
                  TTLs expire.
                  Another special keyword <strong class="userinput"><code>unlimited</code></strong>
                  means the maximum value of 32-bit unsigned integers
                  (0xffffffff), which may not have the same effect as
                  0 on machines that support more than 32 bits of
                  memory space.
                  Any positive values less than 2MB will be ignored reset
                  to 2MB.
                  In a server with multiple views, the limit applies
                  separately to the cache of each view.
                  The default is 0.
                </p></dd>
<dt><span class="term"><span><strong class="command">tcp-listen-queue</strong></span></span></dt>
<dd><p>
                  The listen queue depth.  The default and minimum is 10.
                  If the kernel supports the accept filter "dataready" this
                  also controls how
                  many TCP connections that will be queued in kernel space
                  waiting for
                  some data before being passed to accept.  Nonzero values
                  less than 10 will be silently raised. A value of 0 may also
                  be used; on most platforms this sets the listen queue 
                  length to a system-defined default value.
                </p></dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2585947"></a>Periodic Task Intervals</h4></div></div></div>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">cleaning-interval</strong></span></span></dt>
<dd><p>
                  This interval is effectively obsolete.  Previously,
                  the server would remove expired resource records
                  from the cache every <span><strong class="command">cleaning-interval</strong></span> minutes.
                  <acronym class="acronym">BIND</acronym> 9 now manages cache
                  memory in a more sophisticated manner and does not
                  rely on the periodic cleaning any more.
                  Specifying this option therefore has no effect on
                  the server's behavior.
                </p></dd>
<dt><span class="term"><span><strong class="command">heartbeat-interval</strong></span></span></dt>
<dd><p>
                  The server will perform zone maintenance tasks
                  for all zones marked as <span><strong class="command">dialup</strong></span> whenever this
                  interval expires. The default is 60 minutes. Reasonable
                  values are up
                  to 1 day (1440 minutes).  The maximum value is 28 days
                  (40320 minutes).
                  If set to 0, no zone maintenance for these zones will occur.
                </p></dd>
<dt><span class="term"><span><strong class="command">interface-interval</strong></span></span></dt>
<dd><p>
                  The server will scan the network interface list
                  every <span><strong class="command">interface-interval</strong></span>
                  minutes. The default
                  is 60 minutes. The maximum value is 28 days (40320 minutes).
                  If set to 0, interface scanning will only occur when
                  the configuration file is  loaded. After the scan, the
                  server will
                  begin listening for queries on any newly discovered
                  interfaces (provided they are allowed by the
                  <span><strong class="command">listen-on</strong></span> configuration), and
                  will
                  stop listening on interfaces that have gone away.
                </p></dd>
<dt><span class="term"><span><strong class="command">statistics-interval</strong></span></span></dt>
<dd>
<p>
                  Name server statistics will be logged
                  every <span><strong class="command">statistics-interval</strong></span>
                  minutes. The default is
                  60. The maximum value is 28 days (40320 minutes).
                  If set to 0, no statistics will be logged.
                  </p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
                    Not yet implemented in
                    <acronym class="acronym">BIND</acronym> 9.
                  </p>
</div>
</dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="topology"></a>Topology</h4></div></div></div>
<p>
            All other things being equal, when the server chooses a name
            server
            to query from a list of name servers, it prefers the one that is
            topologically closest to itself. The <span><strong class="command">topology</strong></span> statement
            takes an <span><strong class="command">address_match_list</strong></span> and
            interprets it
            in a special way. Each top-level list element is assigned a
            distance.
            Non-negated elements get a distance based on their position in the
            list, where the closer the match is to the start of the list, the
            shorter the distance is between it and the server. A negated match
            will be assigned the maximum distance from the server. If there
            is no match, the address will get a distance which is further than
            any non-negated list element, and closer than any negated element.
            For example,
          </p>
<pre class="programlisting">topology {
    10/8;
    !1.2.3/24;
    { 1.2/16; 3/8; };
};</pre>
<p>
            will prefer servers on network 10 the most, followed by hosts
            on network 1.2.0.0 (netmask 255.255.0.0) and network 3, with the
            exception of hosts on network 1.2.3 (netmask 255.255.255.0), which
            is preferred least of all.
          </p>
<p>
            The default topology is
          </p>
<pre class="programlisting">    topology { localhost; localnets; };
</pre>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
              The <span><strong class="command">topology</strong></span> option
              is not implemented in <acronym class="acronym">BIND</acronym> 9.
            </p>
</div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="the_sortlist_statement"></a>The <span><strong class="command">sortlist</strong></span> Statement</h4></div></div></div>
<p>
            The response to a DNS query may consist of multiple resource
            records (RRs) forming a resource records set (RRset).
            The name server will normally return the
            RRs within the RRset in an indeterminate order
            (but see the <span><strong class="command">rrset-order</strong></span>
            statement in <a href="Bv9ARM.ch06.html#rrset_ordering" title="RRset Ordering">the section called &#8220;RRset Ordering&#8221;</a>).
            The client resolver code should rearrange the RRs as appropriate,
            that is, using any addresses on the local net in preference to
            other addresses.
            However, not all resolvers can do this or are correctly
            configured.
            When a client is using a local server, the sorting can be performed
            in the server, based on the client's address. This only requires
            configuring the name servers, not all the clients.
          </p>
<p>
            The <span><strong class="command">sortlist</strong></span> statement (see below)
            takes
            an <span><strong class="command">address_match_list</strong></span> and
            interprets it even
            more specifically than the <span><strong class="command">topology</strong></span>
            statement
            does (<a href="Bv9ARM.ch06.html#topology" title="Topology">the section called &#8220;Topology&#8221;</a>).
            Each top level statement in the <span><strong class="command">sortlist</strong></span> must
            itself be an explicit <span><strong class="command">address_match_list</strong></span> with
            one or two elements. The first element (which may be an IP
            address,
            an IP prefix, an ACL name or a nested <span><strong class="command">address_match_list</strong></span>)
            of each top level list is checked against the source address of
            the query until a match is found.
          </p>
<p>
            Once the source address of the query has been matched, if
            the top level statement contains only one element, the actual
            primitive
            element that matched the source address is used to select the
            address
            in the response to move to the beginning of the response. If the
            statement is a list of two elements, then the second element is
            treated the same as the <span><strong class="command">address_match_list</strong></span> in
            a <span><strong class="command">topology</strong></span> statement. Each top
            level element
            is assigned a distance and the address in the response with the
            minimum
            distance is moved to the beginning of the response.
          </p>
<p>
            In the following example, any queries received from any of
            the addresses of the host itself will get responses preferring
            addresses
            on any of the locally connected networks. Next most preferred are
            addresses
            on the 192.168.1/24 network, and after that either the
            192.168.2/24
            or
            192.168.3/24 network with no preference shown between these two
            networks. Queries received from a host on the 192.168.1/24 network
            will prefer other addresses on that network to the 192.168.2/24
            and
            192.168.3/24 networks. Queries received from a host on the
            192.168.4/24
            or the 192.168.5/24 network will only prefer other addresses on
            their directly connected networks.
          </p>
<pre class="programlisting">sortlist {
    // IF the local host
    // THEN first fit on the following nets
    { localhost;
        { localnets;
            192.168.1/24;
            { 192.168.2/24; 192.168.3/24; }; }; };
    // IF on class C 192.168.1 THEN use .1, or .2 or .3
    { 192.168.1/24;
        { 192.168.1/24;
            { 192.168.2/24; 192.168.3/24; }; }; };
    // IF on class C 192.168.2 THEN use .2, or .1 or .3
    { 192.168.2/24;
        { 192.168.2/24;
            { 192.168.1/24; 192.168.3/24; }; }; };
    // IF on class C 192.168.3 THEN use .3, or .1 or .2
    { 192.168.3/24;
        { 192.168.3/24;
            { 192.168.1/24; 192.168.2/24; }; }; };
    // IF .4 or .5 THEN prefer that net
    { { 192.168.4/24; 192.168.5/24; };
    };
};</pre>
<p>
            The following example will give reasonable behavior for the
            local host and hosts on directly connected networks. It is similar
            to the behavior of the address sort in <acronym class="acronym">BIND</acronym> 4.9.x. Responses sent
            to queries from the local host will favor any of the directly
            connected
            networks. Responses sent to queries from any other hosts on a
            directly
            connected network will prefer addresses on that same network.
            Responses
            to other queries will not be sorted.
          </p>
<pre class="programlisting">sortlist {
           { localhost; localnets; };
           { localnets; };
};
</pre>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="rrset_ordering"></a>RRset Ordering</h4></div></div></div>
<p>
            When multiple records are returned in an answer it may be
            useful to configure the order of the records placed into the
            response.
            The <span><strong class="command">rrset-order</strong></span> statement permits
            configuration
            of the ordering of the records in a multiple record response.
            See also the <span><strong class="command">sortlist</strong></span> statement,
            <a href="Bv9ARM.ch06.html#the_sortlist_statement" title="The sortlist Statement">the section called &#8220;The <span><strong class="command">sortlist</strong></span> Statement&#8221;</a>.
          </p>
<p>
            An <span><strong class="command">order_spec</strong></span> is defined as
            follows:
          </p>
<p>
            [<span class="optional">class <em class="replaceable"><code>class_name</code></em></span>]
            [<span class="optional">type <em class="replaceable"><code>type_name</code></em></span>]
            [<span class="optional">name <em class="replaceable"><code>"domain_name"</code></em></span>]
            order <em class="replaceable"><code>ordering</code></em>
          </p>
<p>
            If no class is specified, the default is <span><strong class="command">ANY</strong></span>.
            If no type is specified, the default is <span><strong class="command">ANY</strong></span>.
            If no name is specified, the default is "<span><strong class="command">*</strong></span>" (asterisk).
          </p>
<p>
            The legal values for <span><strong class="command">ordering</strong></span> are:
          </p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                    <p><span><strong class="command">fixed</strong></span></p>
                  </td>
<td>
                    <p>
                      Records are returned in the order they
                      are defined in the zone file.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">random</strong></span></p>
                  </td>
<td>
                    <p>
                      Records are returned in some random order.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p><span><strong class="command">cyclic</strong></span></p>
                  </td>
<td>
                    <p>
                      Records are returned in a cyclic round-robin order.
                    </p>
                    <p>
                      If <acronym class="acronym">BIND</acronym> is configured with the
                      "--enable-fixed-rrset" option at compile time, then
                      the initial ordering of the RRset will match the
                      one specified in the zone file.
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<p>
            For example:
          </p>
<pre class="programlisting">rrset-order {
   class IN type A name "host.example.com" order random;
   order cyclic;
};
</pre>
<p>
            will cause any responses for type A records in class IN that
            have "<code class="literal">host.example.com</code>" as a
            suffix, to always be returned
            in random order. All other records are returned in cyclic order.
          </p>
<p>
            If multiple <span><strong class="command">rrset-order</strong></span> statements
            appear, they are not combined &#8212; the last one applies.
          </p>
<p>
            By default, all records are returned in random order.
          </p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
              In this release of <acronym class="acronym">BIND</acronym> 9, the
              <span><strong class="command">rrset-order</strong></span> statement does not support
              "fixed" ordering by default.  Fixed ordering can be enabled
              at compile time by specifying "--enable-fixed-rrset" on
              the "configure" command line.
            </p>
</div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="tuning"></a>Tuning</h4></div></div></div>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">lame-ttl</strong></span></span></dt>
<dd>
<p>
                  Sets the number of seconds to cache a
                  lame server indication. 0 disables caching. (This is
                  <span class="bold"><strong>NOT</strong></span> recommended.)
                  The default is <code class="literal">600</code> (10 minutes) and the
                  maximum value is
                  <code class="literal">1800</code> (30 minutes).
                </p>
<p>
                  Lame-ttl also controls the amount of time DNSSEC
                  validation failures are cached.  There is a minimum
                  of 30 seconds applied to bad cache entries if the
                  lame-ttl is set to less than 30 seconds.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">max-ncache-ttl</strong></span></span></dt>
<dd><p>
                  To reduce network traffic and increase performance,
                  the server stores negative answers. <span><strong class="command">max-ncache-ttl</strong></span> is
                  used to set a maximum retention time for these answers in
                  the server
                  in seconds. The default
                  <span><strong class="command">max-ncache-ttl</strong></span> is <code class="literal">10800</code> seconds (3 hours).
                  <span><strong class="command">max-ncache-ttl</strong></span> cannot exceed
                  7 days and will
                  be silently truncated to 7 days if set to a greater value.
                </p></dd>
<dt><span class="term"><span><strong class="command">max-cache-ttl</strong></span></span></dt>
<dd><p>
                  Sets the maximum time for which the server will
                  cache ordinary (positive) answers. The default is
                  one week (7 days).
                  A value of zero may cause all queries to return
                  SERVFAIL, because of lost caches of intermediate
                  RRsets (such as NS and glue AAAA/A records) in the
                  resolution process.
                </p></dd>
<dt><span class="term"><span><strong class="command">min-roots</strong></span></span></dt>
<dd>
<p>
                  The minimum number of root servers that
                  is required for a request for the root servers to be
                  accepted. The default
                  is <strong class="userinput"><code>2</code></strong>.
                </p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
                    Not implemented in <acronym class="acronym">BIND</acronym> 9.
                  </p>
</div>
</dd>
<dt><span class="term"><span><strong class="command">sig-validity-interval</strong></span></span></dt>
<dd>
<p>
                  Specifies the number of days into the future when
                  DNSSEC signatures automatically generated as a
                  result of dynamic updates (<a href="Bv9ARM.ch04.html#dynamic_update" title="Dynamic Update">the section called &#8220;Dynamic Update&#8221;</a>) will expire.  There
                  is an optional second field which specifies how
                  long before expiry that the signatures will be
                  regenerated.  If not specified, the signatures will
                  be regenerated at 1/4 of base interval.  The second
                  field is specified in days if the base interval is
                  greater than 7 days otherwise it is specified in hours.
                  The default base interval is <code class="literal">30</code> days
                  giving a re-signing interval of 7 1/2 days.  The maximum
                  values are 10 years (3660 days).
                </p>
<p>
                  The signature inception time is unconditionally
                  set to one hour before the current time to allow
                  for a limited amount of clock skew.
                </p>
<p>
                  The <span><strong class="command">sig-validity-interval</strong></span>
                  should be, at least, several multiples of the SOA
                  expire interval to allow for reasonable interaction
                  between the various timer and expiry dates.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">sig-signing-nodes</strong></span></span></dt>
<dd><p>
                  Specify the maximum number of nodes to be
                  examined in each quantum when signing a zone with
                  a new DNSKEY. The default is
                  <code class="literal">100</code>.
                </p></dd>
<dt><span class="term"><span><strong class="command">sig-signing-signatures</strong></span></span></dt>
<dd><p>
                  Specify a threshold number of signatures that
                  will terminate processing a quantum when signing
                  a zone with a new DNSKEY.  The default is
                  <code class="literal">10</code>.
                </p></dd>
<dt><span class="term"><span><strong class="command">sig-signing-type</strong></span></span></dt>
<dd>
<p>
                  Specify a private RDATA type to be used when generating
                  signing state records.  The default is
                  <code class="literal">65534</code>.
                </p>
<p>
                  It is expected that this parameter may be removed
                  in a future version once there is a standard type.
                </p>
<p>
                  Signing state records are used to internally by
                  <span><strong class="command">named</strong></span> to track the current state of
                  a zone-signing process, i.e., whether it is still active
                  or has been completed.  The records can be inspected
                  using the command
                  <span><strong class="command">rndc signing -list <em class="replaceable"><code>zone</code></em></strong></span>.
                  Once <span><strong class="command">named</strong></span> has finished signing
                  a zone with a particular key, the signing state
                  record associated with that key can be removed from
                  the zone by running
                  <span><strong class="command">rndc signing -clear <em class="replaceable"><code>keyid/algorithm</code></em> <em class="replaceable"><code>zone</code></em></strong></span>.
                  To clear all of the completed signing state
                  records for a zone, use
                  <span><strong class="command">rndc signing -clear all <em class="replaceable"><code>zone</code></em></strong></span>.
                </p>
</dd>
<dt>
<span class="term"><span><strong class="command">min-refresh-time</strong></span>, </span><span class="term"><span><strong class="command">max-refresh-time</strong></span>, </span><span class="term"><span><strong class="command">min-retry-time</strong></span>, </span><span class="term"><span><strong class="command">max-retry-time</strong></span></span>
</dt>
<dd>
<p>
                  These options control the server's behavior on refreshing a
                  zone
                  (querying for SOA changes) or retrying failed transfers.
                  Usually the SOA values for the zone are used, but these
                  values
                  are set by the master, giving slave server administrators
                  little
                  control over their contents.
                </p>
<p>
                  These options allow the administrator to set a minimum and
                  maximum
                  refresh and retry time either per-zone, per-view, or
                  globally.
                  These options are valid for slave and stub zones,
                  and clamp the SOA refresh and retry times to the specified
                  values.
                </p>
<p>
                  The following defaults apply.
                  <span><strong class="command">min-refresh-time</strong></span> 300 seconds,
                  <span><strong class="command">max-refresh-time</strong></span> 2419200 seconds
                  (4 weeks), <span><strong class="command">min-retry-time</strong></span> 500 seconds,
                  and <span><strong class="command">max-retry-time</strong></span> 1209600 seconds
                  (2 weeks).
                </p>
</dd>
<dt><span class="term"><span><strong class="command">edns-udp-size</strong></span></span></dt>
<dd>
<p>
                  Sets the advertised EDNS UDP buffer size in bytes
                  to control the size of packets received.
                  Valid values are 512 to 4096 (values outside this range
                  will be silently adjusted).  The default value
                  is 4096.  The usual reason for setting
                  <span><strong class="command">edns-udp-size</strong></span> to a non-default
                  value is to get UDP answers to pass through broken
                  firewalls that block fragmented packets and/or
                  block UDP packets that are greater than 512 bytes.
                </p>
<p>
                  <span><strong class="command">named</strong></span> will fallback to using 512 bytes
                  if it get a series of timeout at the initial value.  512
                  bytes is not being offered to encourage sites to fix their
                  firewalls.  Small EDNS UDP sizes will result in the
                  excessive use of TCP.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">max-udp-size</strong></span></span></dt>
<dd>
<p>
                  Sets the maximum EDNS UDP message size
                  <span><strong class="command">named</strong></span> will send in bytes.
                  Valid values are 512 to 4096 (values outside this
                  range will be silently adjusted).  The default
                  value is 4096.  The usual reason for setting
                  <span><strong class="command">max-udp-size</strong></span> to a non-default
                  value is to get UDP answers to pass through broken
                  firewalls that block fragmented packets and/or
                  block UDP packets that are greater than 512 bytes.
                  This is independent of the advertised receive
                  buffer (<span><strong class="command">edns-udp-size</strong></span>).
                </p>
<p>
                  Setting this to a low value will encourage additional
                  TCP traffic to the nameserver.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">masterfile-format</strong></span></span></dt>
<dd>
<p>Specifies
                  the file format of zone files (see
                  <a href="Bv9ARM.ch06.html#zonefile_format" title="Additional File Formats">the section called &#8220;Additional File Formats&#8221;</a>).
                  The default value is <code class="constant">text</code>, which is the
                  standard textual representation, except for slave zones,
                  in which the default value is <code class="constant">raw</code>.
                  Files in other formats than <code class="constant">text</code> are
                  typically expected to be generated by the
                  <span><strong class="command">named-compilezone</strong></span> tool, or dumped by
                  <span><strong class="command">named</strong></span>.
                </p>
<p>
                  Note that when a zone file in a different format than
                  <code class="constant">text</code> is loaded, <span><strong class="command">named</strong></span>
                  may omit some of the checks which would be performed for a
                  file in the <code class="constant">text</code> format.  In particular,
                  <span><strong class="command">check-names</strong></span> checks do not apply
                  for the <code class="constant">raw</code> format.  This means
                  a zone file in the <code class="constant">raw</code> format
                  must be generated with the same check level as that
                  specified in the <span><strong class="command">named</strong></span> configuration
                  file.  This statement sets the
                  <span><strong class="command">masterfile-format</strong></span> for all zones,
                  but can be overridden on a per-zone or per-view basis
                  by including a <span><strong class="command">masterfile-format</strong></span>
                  statement within the <span><strong class="command">zone</strong></span> or
                  <span><strong class="command">view</strong></span> block in the configuration
                  file.
                </p>
</dd>
<dt>
<a name="clients-per-query"></a><span class="term"><span><strong class="command">clients-per-query</strong></span>, </span><span class="term"><span><strong class="command">max-clients-per-query</strong></span></span>
</dt>
<dd>
<p>These set the
                  initial value (minimum) and maximum number of recursive
                  simultaneous clients for any given query
                  (&lt;qname,qtype,qclass&gt;) that the server will accept
                  before dropping additional clients.  <span><strong class="command">named</strong></span> will attempt to
                  self tune this value and changes will be logged.  The
                  default values are 10 and 100.
                </p>
<p>
                  This value should reflect how many queries come in for
                  a given name in the time it takes to resolve that name.
                  If the number of queries exceed this value, <span><strong class="command">named</strong></span> will
                  assume that it is dealing with a non-responsive zone
                  and will drop additional queries.  If it gets a response
                  after dropping queries, it will raise the estimate.  The
                  estimate will then be lowered in 20 minutes if it has
                  remained unchanged.
                </p>
<p>
                  If <span><strong class="command">clients-per-query</strong></span> is set to zero,
                  then there is no limit on the number of clients per query
                  and no queries will be dropped.
                </p>
<p>
                  If <span><strong class="command">max-clients-per-query</strong></span> is set to zero,
                  then there is no upper bound other than imposed by
                  <span><strong class="command">recursive-clients</strong></span>.
                </p>
</dd>
<dt>
<a name="max-recursion-depth"></a><span class="term"><span><strong class="command">max-recursion-depth</strong></span></span>
</dt>
<dd><p>
                  Sets the maximum number of levels of recursion
                  that are permitted at any one time while servicing
                  a recursive query. Resolving a name may require
                  looking up a name server address, which in turn
                  requires resolving another name, etc; if the number
                  of indirections exceeds this value, the recursive
                  query is terminated and returns SERVFAIL.  The
                  default is 7.
                </p></dd>
<dt>
<a name="max-recursion-queries"></a><span class="term"><span><strong class="command">max-recursion-queries</strong></span></span>
</dt>
<dd><p>
                  Sets the maximum number of iterative queries that
                  may be sent while servicing a recursive query.
                  If more queries are sent, the recursive query
                  is terminated and returns SERVFAIL. Queries to
                  look up top level comains such as "com" and "net"
                  and the DNS root zone are exempt from this limitation.
                  The default is 50.
                </p></dd>
<dt><span class="term"><span><strong class="command">notify-delay</strong></span></span></dt>
<dd>
<p>
                  The delay, in seconds, between sending sets of notify
                  messages for a zone.  The default is five (5) seconds.
                </p>
<p>
                  The overall rate that NOTIFY messages are sent for all
                  zones is controlled by <span><strong class="command">serial-query-rate</strong></span>.
                </p>
</dd>
<dt><span class="term"><span><strong class="command">max-rsa-exponent-size</strong></span></span></dt>
<dd><p>
                  The maximum RSA exponent size, in bits, that will
                  be accepted when validating.  Valid values are 35
                  to 4096 bits.  The default zero (0) is also accepted
                  and is equivalent to 4096.
                </p></dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="builtin"></a>Built-in server information zones</h4></div></div></div>
<p>
            The server provides some helpful diagnostic information
            through a number of built-in zones under the
            pseudo-top-level-domain <code class="literal">bind</code> in the
            <span><strong class="command">CHAOS</strong></span> class.  These zones are part
            of a
            built-in view (see <a href="Bv9ARM.ch06.html#view_statement_grammar" title="view Statement Grammar">the section called &#8220;<span><strong class="command">view</strong></span> Statement Grammar&#8221;</a>) of
            class
            <span><strong class="command">CHAOS</strong></span> which is separate from the
            default view of class <span><strong class="command">IN</strong></span>. Most global
            configuration options (<span><strong class="command">allow-query</strong></span>,
            etc) will apply to this view, but some are locally
            overridden: <span><strong class="command">notify</strong></span>,
            <span><strong class="command">recursion</strong></span> and
            <span><strong class="command">allow-new-zones</strong></span> are
            always set to <strong class="userinput"><code>no</code></strong>.
          </p>
<p>
            If you need to disable these zones, use the options
            below, or hide the built-in <span><strong class="command">CHAOS</strong></span>
            view by
            defining an explicit view of class <span><strong class="command">CHAOS</strong></span>
            that matches all clients.
          </p>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">version</strong></span></span></dt>
<dd><p>
                  The version the server should report
                  via a query of the name <code class="literal">version.bind</code>
                  with type <span><strong class="command">TXT</strong></span>, class <span><strong class="command">CHAOS</strong></span>.
                  The default is the real version number of this server.
                  Specifying <span><strong class="command">version none</strong></span>
                  disables processing of the queries.
                </p></dd>
<dt><span class="term"><span><strong class="command">hostname</strong></span></span></dt>
<dd><p>
                  The hostname the server should report via a query of
                  the name <code class="filename">hostname.bind</code>
                  with type <span><strong class="command">TXT</strong></span>, class <span><strong class="command">CHAOS</strong></span>.
                  This defaults to the hostname of the machine hosting the
                  name server as
                  found by the gethostname() function.  The primary purpose of such queries
                  is to
                  identify which of a group of anycast servers is actually
                  answering your queries.  Specifying <span><strong class="command">hostname none;</strong></span>
                  disables processing of the queries.
                </p></dd>
<dt><span class="term"><span><strong class="command">server-id</strong></span></span></dt>
<dd><p>
                  The ID the server should report when receiving a Name
                  Server Identifier (NSID) query, or a query of the name
                  <code class="filename">ID.SERVER</code> with type
                  <span><strong class="command">TXT</strong></span>, class <span><strong class="command">CHAOS</strong></span>.
                  The primary purpose of such queries is to
                  identify which of a group of anycast servers is actually
                  answering your queries.  Specifying <span><strong class="command">server-id none;</strong></span>
                  disables processing of the queries.
                  Specifying <span><strong class="command">server-id hostname;</strong></span> will cause <span><strong class="command">named</strong></span> to
                  use the hostname as found by the gethostname() function.
                  The default <span><strong class="command">server-id</strong></span> is <span><strong class="command">none</strong></span>.
                </p></dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="empty"></a>Built-in Empty Zones</h4></div></div></div>
<p>
            Named has some built-in empty zones (SOA and NS records only).
            These are for zones that should normally be answered locally
            and which queries should not be sent to the Internet's root
            servers.  The official servers which cover these namespaces
            return NXDOMAIN responses to these queries.  In particular,
            these cover the reverse namespaces for addresses from
            RFC 1918, RFC 4193, RFC 5737 and RFC 6598.  They also include the
            reverse namespace for IPv6 local address (locally assigned),
            IPv6 link local addresses, the IPv6 loopback address and the
            IPv6 unknown address.
          </p>
<p>
            Named will attempt to determine if a built-in zone already exists
            or is active (covered by a forward-only forwarding declaration)
            and will not create an empty zone in that case.
          </p>
<p>
            The current list of empty zones is:
            </p>
<div class="itemizedlist"><ul type="disc">
<li>10.IN-ADDR.ARPA</li>
<li>16.172.IN-ADDR.ARPA</li>
<li>17.172.IN-ADDR.ARPA</li>
<li>18.172.IN-ADDR.ARPA</li>
<li>19.172.IN-ADDR.ARPA</li>
<li>20.172.IN-ADDR.ARPA</li>
<li>21.172.IN-ADDR.ARPA</li>
<li>22.172.IN-ADDR.ARPA</li>
<li>23.172.IN-ADDR.ARPA</li>
<li>24.172.IN-ADDR.ARPA</li>
<li>25.172.IN-ADDR.ARPA</li>
<li>26.172.IN-ADDR.ARPA</li>
<li>27.172.IN-ADDR.ARPA</li>
<li>28.172.IN-ADDR.ARPA</li>
<li>29.172.IN-ADDR.ARPA</li>
<li>30.172.IN-ADDR.ARPA</li>
<li>31.172.IN-ADDR.ARPA</li>
<li>168.192.IN-ADDR.ARPA</li>
<li>64.100.IN-ADDR.ARPA</li>
<li>65.100.IN-ADDR.ARPA</li>
<li>66.100.IN-ADDR.ARPA</li>
<li>67.100.IN-ADDR.ARPA</li>
<li>68.100.IN-ADDR.ARPA</li>
<li>69.100.IN-ADDR.ARPA</li>
<li>70.100.IN-ADDR.ARPA</li>
<li>71.100.IN-ADDR.ARPA</li>
<li>72.100.IN-ADDR.ARPA</li>
<li>73.100.IN-ADDR.ARPA</li>
<li>74.100.IN-ADDR.ARPA</li>
<li>75.100.IN-ADDR.ARPA</li>
<li>76.100.IN-ADDR.ARPA</li>
<li>77.100.IN-ADDR.ARPA</li>
<li>78.100.IN-ADDR.ARPA</li>
<li>79.100.IN-ADDR.ARPA</li>
<li>80.100.IN-ADDR.ARPA</li>
<li>81.100.IN-ADDR.ARPA</li>
<li>82.100.IN-ADDR.ARPA</li>
<li>83.100.IN-ADDR.ARPA</li>
<li>84.100.IN-ADDR.ARPA</li>
<li>85.100.IN-ADDR.ARPA</li>
<li>86.100.IN-ADDR.ARPA</li>
<li>87.100.IN-ADDR.ARPA</li>
<li>88.100.IN-ADDR.ARPA</li>
<li>89.100.IN-ADDR.ARPA</li>
<li>90.100.IN-ADDR.ARPA</li>
<li>91.100.IN-ADDR.ARPA</li>
<li>92.100.IN-ADDR.ARPA</li>
<li>93.100.IN-ADDR.ARPA</li>
<li>94.100.IN-ADDR.ARPA</li>
<li>95.100.IN-ADDR.ARPA</li>
<li>96.100.IN-ADDR.ARPA</li>
<li>97.100.IN-ADDR.ARPA</li>
<li>98.100.IN-ADDR.ARPA</li>
<li>99.100.IN-ADDR.ARPA</li>
<li>100.100.IN-ADDR.ARPA</li>
<li>101.100.IN-ADDR.ARPA</li>
<li>102.100.IN-ADDR.ARPA</li>
<li>103.100.IN-ADDR.ARPA</li>
<li>104.100.IN-ADDR.ARPA</li>
<li>105.100.IN-ADDR.ARPA</li>
<li>106.100.IN-ADDR.ARPA</li>
<li>107.100.IN-ADDR.ARPA</li>
<li>108.100.IN-ADDR.ARPA</li>
<li>109.100.IN-ADDR.ARPA</li>
<li>110.100.IN-ADDR.ARPA</li>
<li>111.100.IN-ADDR.ARPA</li>
<li>112.100.IN-ADDR.ARPA</li>
<li>113.100.IN-ADDR.ARPA</li>
<li>114.100.IN-ADDR.ARPA</li>
<li>115.100.IN-ADDR.ARPA</li>
<li>116.100.IN-ADDR.ARPA</li>
<li>117.100.IN-ADDR.ARPA</li>
<li>118.100.IN-ADDR.ARPA</li>
<li>119.100.IN-ADDR.ARPA</li>
<li>120.100.IN-ADDR.ARPA</li>
<li>121.100.IN-ADDR.ARPA</li>
<li>122.100.IN-ADDR.ARPA</li>
<li>123.100.IN-ADDR.ARPA</li>
<li>124.100.IN-ADDR.ARPA</li>
<li>125.100.IN-ADDR.ARPA</li>
<li>126.100.IN-ADDR.ARPA</li>
<li>127.100.IN-ADDR.ARPA</li>
<li>0.IN-ADDR.ARPA</li>
<li>127.IN-ADDR.ARPA</li>
<li>254.169.IN-ADDR.ARPA</li>
<li>2.0.192.IN-ADDR.ARPA</li>
<li>100.51.198.IN-ADDR.ARPA</li>
<li>113.0.203.IN-ADDR.ARPA</li>
<li>255.255.255.255.IN-ADDR.ARPA</li>
<li>0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA</li>
<li>1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA</li>
<li>8.B.D.0.1.0.0.2.IP6.ARPA</li>
<li>D.F.IP6.ARPA</li>
<li>8.E.F.IP6.ARPA</li>
<li>9.E.F.IP6.ARPA</li>
<li>A.E.F.IP6.ARPA</li>
<li>B.E.F.IP6.ARPA</li>
</ul></div>
<p>
          </p>
<p>
            Empty zones are settable at the view level and only apply to
            views of class IN.  Disabled empty zones are only inherited
            from options if there are no disabled empty zones specified
            at the view level.  To override the options list of disabled
            zones, you can disable the root zone at the view level, for example:
</p>
<pre class="programlisting">
            disable-empty-zone ".";
</pre>
<p>
          </p>
<p>
            If you are using the address ranges covered here, you should
            already have reverse zones covering the addresses you use.
            In practice this appears to not be the case with many queries
            being made to the infrastructure servers for names in these
            spaces.  So many in fact that sacrificial servers were needed
            to be deployed to channel the query load away from the
            infrastructure servers.
          </p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
            The real parent servers for these zones should disable all
            empty zone under the parent zone they serve.  For the real
            root servers, this is all built-in empty zones.  This will
            enable them to return referrals to deeper in the tree.
          </div>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">empty-server</strong></span></span></dt>
<dd><p>
                  Specify what server name will appear in the returned
                  SOA record for empty zones.  If none is specified, then
                  the zone's name will be used.
                </p></dd>
<dt><span class="term"><span><strong class="command">empty-contact</strong></span></span></dt>
<dd><p>
                  Specify what contact name will appear in the returned
                  SOA record for empty zones.  If none is specified, then
                  "." will be used.
                </p></dd>
<dt><span class="term"><span><strong class="command">empty-zones-enable</strong></span></span></dt>
<dd><p>
                  Enable or disable all empty zones.  By default, they
                  are enabled.
                </p></dd>
<dt><span class="term"><span><strong class="command">disable-empty-zone</strong></span></span></dt>
<dd><p>
                  Disable individual empty zones.  By default, none are
                  disabled.  This option can be specified multiple times.
                </p></dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="acache"></a>Additional Section Caching</h4></div></div></div>
<p>
            The additional section cache, also called <span><strong class="command">acache</strong></span>,
            is an internal cache to improve the response performance of BIND 9.
            When additional section caching is enabled, BIND 9 will
            cache an internal short-cut to the additional section content for
            each answer RR.
            Note that <span><strong class="command">acache</strong></span> is an internal caching
            mechanism of BIND 9, and is not related to the DNS caching
            server function.
          </p>
<p>
            Additional section caching does not change the
            response content (except the RRsets ordering of the additional
            section, see below), but can improve the response performance
            significantly.
            It is particularly effective when BIND 9 acts as an authoritative
            server for a zone that has many delegations with many glue RRs.
          </p>
<p>
            In order to obtain the maximum performance improvement
            from additional section caching, setting
            <span><strong class="command">additional-from-cache</strong></span>
            to <span><strong class="command">no</strong></span> is recommended, since the current
            implementation of <span><strong class="command">acache</strong></span>
            does not short-cut of additional section information from the
            DNS cache data.
          </p>
<p>
            One obvious disadvantage of <span><strong class="command">acache</strong></span> is
            that it requires much more
            memory for the internal cached data.
            Thus, if the response performance does not matter and memory
            consumption is much more critical, the
            <span><strong class="command">acache</strong></span> mechanism can be
            disabled by setting <span><strong class="command">acache-enable</strong></span> to
            <span><strong class="command">no</strong></span>.
            It is also possible to specify the upper limit of memory
            consumption
            for acache by using <span><strong class="command">max-acache-size</strong></span>.
          </p>
<p>
            Additional section caching also has a minor effect on the
            RRset ordering in the additional section.
            Without <span><strong class="command">acache</strong></span>,
            <span><strong class="command">cyclic</strong></span> order is effective for the additional
            section as well as the answer and authority sections.
            However, additional section caching fixes the ordering when it
            first caches an RRset for the additional section, and the same
            ordering will be kept in succeeding responses, regardless of the
            setting of <span><strong class="command">rrset-order</strong></span>.
            The effect of this should be minor, however, since an
            RRset in the additional section
            typically only contains a small number of RRs (and in many cases
            it only contains a single RR), in which case the
            ordering does not matter much.
          </p>
<p>
            The following is a summary of options related to
            <span><strong class="command">acache</strong></span>.
          </p>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">acache-enable</strong></span></span></dt>
<dd><p>
                  If <span><strong class="command">yes</strong></span>, additional section caching is
                  enabled.  The default value is <span><strong class="command">no</strong></span>.
                </p></dd>
<dt><span class="term"><span><strong class="command">acache-cleaning-interval</strong></span></span></dt>
<dd><p>
                  The server will remove stale cache entries, based on an LRU
                  based
                  algorithm, every <span><strong class="command">acache-cleaning-interval</strong></span> minutes.
                  The default is 60 minutes.
                  If set to 0, no periodic cleaning will occur.
                </p></dd>
<dt><span class="term"><span><strong class="command">max-acache-size</strong></span></span></dt>
<dd><p>
                  The maximum amount of memory in bytes to use for the server's acache.
                  When the amount of data in the acache reaches this limit,
                  the server
                  will clean more aggressively so that the limit is not
                  exceeded.
                  In a server with multiple views, the limit applies
                  separately to the
                  acache of each view.
                  The default is <code class="literal">16M</code>.
                </p></dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2588571"></a>Content Filtering</h4></div></div></div>
<p>
            <acronym class="acronym">BIND</acronym> 9 provides the ability to filter
            out DNS responses from external DNS servers containing
            certain types of data in the answer section.
            Specifically, it can reject address (A or AAAA) records if
            the corresponding IPv4 or IPv6 addresses match the given
            <code class="varname">address_match_list</code> of the
            <span><strong class="command">deny-answer-addresses</strong></span> option.
            It can also reject CNAME or DNAME records if the "alias"
            name (i.e., the CNAME alias or the substituted query name
            due to DNAME) matches the
            given <code class="varname">namelist</code> of the
            <span><strong class="command">deny-answer-aliases</strong></span> option, where
            "match" means the alias name is a subdomain of one of
            the <code class="varname">name_list</code> elements.
            If the optional <code class="varname">namelist</code> is specified
            with <span><strong class="command">except-from</strong></span>, records whose query name
            matches the list will be accepted regardless of the filter
            setting.
            Likewise, if the alias name is a subdomain of the
            corresponding zone, the <span><strong class="command">deny-answer-aliases</strong></span>
            filter will not apply;
            for example, even if "example.com" is specified for
            <span><strong class="command">deny-answer-aliases</strong></span>,
          </p>
<pre class="programlisting">www.example.com. CNAME xxx.example.com.</pre>
<p>
            returned by an "example.com" server will be accepted.
          </p>
<p>
            In the <code class="varname">address_match_list</code> of the
            <span><strong class="command">deny-answer-addresses</strong></span> option, only
            <code class="varname">ip_addr</code>
            and <code class="varname">ip_prefix</code>
            are meaningful;
            any <code class="varname">key_id</code> will be silently ignored.
          </p>
<p>
            If a response message is rejected due to the filtering,
            the entire message is discarded without being cached, and
            a SERVFAIL error will be returned to the client.
          </p>
<p>
            This filtering is intended to prevent "DNS rebinding attacks," in
            which an attacker, in response to a query for a domain name the
            attacker controls, returns an IP address within your own network or
            an alias name within your own domain.
            A naive web browser or script could then serve as an
            unintended proxy, allowing the attacker
            to get access to an internal node of your local network
            that couldn't be externally accessed otherwise.
            See the paper available at
            <a href="http://portal.acm.org/citation.cfm?id=1315245.1315298" target="_top">
            http://portal.acm.org/citation.cfm?id=1315245.1315298
            </a>
            for more details about the attacks.
          </p>
<p>
            For example, if you own a domain named "example.net" and
            your internal network uses an IPv4 prefix 192.0.2.0/24,
            you might specify the following rules:
          </p>
<pre class="programlisting">deny-answer-addresses { 192.0.2.0/24; } except-from { "example.net"; };
deny-answer-aliases { "example.net"; };
</pre>
<p>
            If an external attacker lets a web browser in your local
            network look up an IPv4 address of "attacker.example.com",
            the attacker's DNS server would return a response like this:
          </p>
<pre class="programlisting">attacker.example.com. A 192.0.2.1</pre>
<p>
            in the answer section.
            Since the rdata of this record (the IPv4 address) matches
            the specified prefix 192.0.2.0/24, this response will be
            ignored.
          </p>
<p>
            On the other hand, if the browser looks up a legitimate
            internal web server "www.example.net" and the
            following response is returned to
            the <acronym class="acronym">BIND</acronym> 9 server
          </p>
<pre class="programlisting">www.example.net. A 192.0.2.2</pre>
<p>
            it will be accepted since the owner name "www.example.net"
            matches the <span><strong class="command">except-from</strong></span> element,
            "example.net".
          </p>
<p>
            Note that this is not really an attack on the DNS per se.
            In fact, there is nothing wrong for an "external" name to
            be mapped to your "internal" IP address or domain name
            from the DNS point of view.
            It might actually be provided for a legitimate purpose,
            such as for debugging.
            As long as the mapping is provided by the correct owner,
            it is not possible or does not make sense to detect
            whether the intent of the mapping is legitimate or not
            within the DNS.
            The "rebinding" attack must primarily be protected at the
            application that uses the DNS.
            For a large site, however, it may be difficult to protect
            all possible applications at once.
            This filtering feature is provided only to help such an
            operational environment;
            it is generally discouraged to turn it on unless you are
            very sure you have no other choice and the attack is a
            real threat for your applications.
          </p>
<p>
            Care should be particularly taken if you want to use this
            option for addresses within 127.0.0.0/8.
            These addresses are obviously "internal", but many
            applications conventionally rely on a DNS mapping from
            some name to such an address.
            Filtering out DNS records containing this address
            spuriously can break such applications.
          </p>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2588765"></a>Response Policy Zone (RPZ) Rewriting</h4></div></div></div>
<p>
            <acronym class="acronym">BIND</acronym> 9 includes a limited
            mechanism to modify DNS responses for requests
            analogous to email anti-spam DNS blacklists.
            Responses can be changed to deny the existence of domains(NXDOMAIN),
            deny the existence of IP addresses for domains (NODATA),
            or contain other IP addresses or data.
          </p>
<p>
            Response policy zones are named in the
            <span><strong class="command">response-policy</strong></span> option for the view or among the
            global options if there is no response-policy option for the view.
            RPZs are ordinary DNS zones containing RRsets
            that can be queried normally if allowed.
            It is usually best to restrict those queries with something like
            <span><strong class="command">allow-query { localhost; };</strong></span>.
          </p>
<p>
            Four policy triggers are encoded in RPZ records, QNAME, IP, NSIP,
            and NSDNAME.
            QNAME RPZ records triggered by query names of requests and targets
            of CNAME records resolved to generate the response.
            The owner name of a QNAME RPZ record is the query name relativized
            to the RPZ.
          </p>
<p>
            The second kind of RPZ trigger is an IP address in an A and AAAA
            record in the ANSWER section of a response.
            IP address triggers are encoded in records that have owner names
            that are subdomains of <strong class="userinput"><code>rpz-ip</code></strong> relativized
            to the RPZ origin name and encode an IP address or address block.
            IPv4 trigger addresses are represented as
            <strong class="userinput"><code>prefixlength.B4.B3.B2.B1.rpz-ip</code></strong>.
            The prefix length must be between 1 and 32.
            All four bytes, B4, B3, B2, and B1, must be present.
            B4 is the decimal value of the least significant byte of the
            IPv4 address as in IN-ADDR.ARPA.
            IPv6 addresses are encoded in a format similar to the standard
            IPv6 text representation,
            <strong class="userinput"><code>prefixlength.W8.W7.W6.W5.W4.W3.W2.W1.rpz-ip</code></strong>.
            Each of W8,...,W1 is a one to four digit hexadecimal number
            representing 16 bits of the IPv6 address as in the standard text
            representation of IPv6 addresses, but reversed as in IN-ADDR.ARPA.
            All 8 words must be present except when consecutive
            zero words are replaced with <strong class="userinput"><code>.zz.</code></strong>
            analogous to double colons (::) in standard IPv6 text encodings.
            The prefix length must be between 1 and 128.
          </p>
<p>
            NSDNAME triggers match names of authoritative servers
            for the query name, a parent of the query name, a CNAME for
            query name, or a parent of a CNAME.
            They are encoded as subdomains of
            <strong class="userinput"><code>rpz-nsdomain</code></strong> relativized
            to the RPZ origin name.
            NSIP triggers match IP addresses in A and
            AAAA RRsets for domains that can be checked against NSDNAME
            policy records.
            NSIP triggers are encoded like IP triggers except as subdomains of
            <strong class="userinput"><code>rpz-nsip</code></strong>.
            NSDNAME and NSIP triggers are checked only for names with at
            least <span><strong class="command">min-ns-dots</strong></span> dots.
            The default value of <span><strong class="command">min-ns-dots</strong></span> is 1 to
            exclude top level domains.
          </p>
<p>
            The query response is checked against all RPZs, so
            two or more policy records can be triggered by a response.
            Because DNS responses can be rewritten according to at most one
            policy record, a single record encoding an action (other than
            <span><strong class="command">DISABLED</strong></span> actions) must be chosen.
            Triggers or the records that encode them are chosen in
            the following order:
            </p>
<div class="itemizedlist"><ul type="disc">
<li>Choose the triggered record in the zone that appears
                first in the response-policy option.
              </li>
<li>Prefer QNAME to IP to NSDNAME to NSIP triggers
                in a single zone.
              </li>
<li>Among NSDNAME triggers, prefer the
                trigger that matches the smallest name under the DNSSEC ordering.
              </li>
<li>Among IP or NSIP triggers, prefer the trigger
                with the longest prefix.
              </li>
<li>Among triggers with the same prefix length,
                prefer the IP or NSIP trigger that matches
                the smallest IP address.
              </li>
</ul></div>
<p>
          </p>
<p>
            When the processing of a response is restarted to resolve
            DNAME or CNAME records and a policy record set has
            not been triggered,
            all RPZs are again consulted for the DNAME or CNAME names
            and addresses.
          </p>
<p>
            RPZ record sets are sets of any types of DNS record except
            DNAME or DNSSEC that encode actions or responses to queries.
            </p>
<div class="itemizedlist"><ul type="disc">
<li>The <span><strong class="command">NXDOMAIN</strong></span> response is encoded
                by a CNAME whose target is the root domain (.)
              </li>
<li>A CNAME whose target is the wildcard top-level
                domain (*.) specifies the <span><strong class="command">NODATA</strong></span> action,
                which rewrites the response to NODATA or ANCOUNT=1.
              </li>
<li>The <span><strong class="command">Local Data</strong></span> action is
                represented by a set ordinary DNS records that are used
                to answer queries.  Queries for record types not the
                set are answered with NODATA.

                A special form of local data is a CNAME whose target is a
                wildcard such as *.example.com.
                It is used as if were an ordinary CNAME after the astrisk (*)
                has been replaced with the query name.
                The purpose for this special form is query logging in the
                walled garden's authority DNS server.
              </li>
<li>The <span><strong class="command">PASSTHRU</strong></span> policy is specified
                by a CNAME whose target is <span><strong class="command">rpz-passthru.</strong></span>
                It causes the response to not be rewritten
                and is most often used to "poke holes" in policies for
                CIDR blocks.
                (A CNAME whose target is the variable part of its owner name
                is an obsolete specification of the PASSTHRU policy.)
              </li>
</ul></div>
<p>
          </p>
<p>
            The actions specified in an RPZ can be overridden with a
            <span><strong class="command">policy</strong></span> clause in the
            <span><strong class="command">response-policy</strong></span> option.
            An organization using an RPZ provided by another organization might
            use this mechanism to redirect domains to its own walled garden.
            </p>
<div class="itemizedlist"><ul type="disc">
<li>
<span><strong class="command">GIVEN</strong></span> says "do not override but
                perform the action specified in the zone."
              </li>
<li>
<span><strong class="command">DISABLED</strong></span> causes policy records to do
                nothing but log what they might have done.
                The response to the DNS query will be written according to
                any triggered policy records that are not disabled.
                Disabled policy zones should appear first,
                because they will often not be logged
                if a higher precedence trigger is found first.
              </li>
<li>
<span><strong class="command">PASSTHRU</strong></span> causes all policy records
                to act as if they were CNAME records with targets the variable
                part of their owner name.  They protect the response from
                being changed.
              </li>
<li>
<span><strong class="command">NXDOMAIN</strong></span> causes all RPZ records
                to specify NXDOMAIN policies.
              </li>
<li>
<span><strong class="command">NODATA</strong></span> overrides with the
                NODATA policy
              </li>
<li>
<span><strong class="command">CNAME domain</strong></span> causes all RPZ
                policy records to act as if they were "cname domain" records.
              </li>
</ul></div>
<p>
          </p>
<p>
            By default, the actions encoded in an RPZ are applied
            only to queries that ask for recursion (RD=1).
            That default can be changed for a single RPZ or all RPZs in a view
            with a <span><strong class="command">recursive-only no</strong></span> clause.
            This feature is useful for serving the same zone files
            both inside and outside an RFC 1918 cloud and using RPZ to
            delete answers that would otherwise contain RFC 1918 values
            on the externally visible name server or view.
          </p>
<p>
            Also by default, RPZ actions are applied only to DNS requests that
            either do not request DNSSEC metadata (DO=0) or when no DNSSEC
            records are available for request name in the original zone (not
            the response policy zone).
            This default can be changed for all RPZs in a view with a
            <span><strong class="command">break-dnssec yes</strong></span> clause.
            In that case, RPZ actions are applied regardless of DNSSEC.
            The name of the clause option reflects the fact that results
            rewritten by RPZ actions cannot verify.
          </p>
<p>
            The TTL of a record modified by RPZ policies is set from the
            TTL of the relevant record in policy zone.  It is then limited
            to a maximum value.
            The <span><strong class="command">max-policy-ttl</strong></span> clause changes that
            maximum from its default of 5.
          </p>
<p>
            For example, you might use this option statement
          </p>
<pre class="programlisting">    response-policy { zone "badlist"; };</pre>
<p>
            and this zone statement
          </p>
<pre class="programlisting">    zone "badlist" {type master; file "master/badlist"; allow-query {none;}; };</pre>
<p>
            with this zone file
          </p>
<pre class="programlisting">$TTL 1H
@                       SOA LOCALHOST. named-mgr.example.com (1 1h 15m 30d 2h)
                        NS  LOCALHOST.

; QNAME policy records.  There are no periods (.) after the owner names.
nxdomain.domain.com     CNAME   .               ; NXDOMAIN policy
nodata.domain.com       CNAME   *.              ; NODATA policy
bad.domain.com          A       10.0.0.1        ; redirect to a walled garden
                        AAAA    2001:2::1

; do not rewrite (PASSTHRU) OK.DOMAIN.COM
ok.domain.com           CNAME   rpz-passthru.

bzone.domain.com        CNAME   garden.example.com.

; redirect x.bzone.domain.com to x.bzone.domain.com.garden.example.com
*.bzone.domain.com      CNAME   *.garden.example.com.


; IP policy records that rewrite all answers for 127/8 except 127.0.0.1
8.0.0.0.127.rpz-ip      CNAME   .
32.1.0.0.127.rpz-ip     CNAME   rpz-passthru.

; NSDNAME and NSIP policy records
ns.domain.com.rpz-nsdname   CNAME   .
48.zz.2.2001.rpz-nsip       CNAME   .
</pre>
<p>
            RPZ can affect server performance.
            Each configured response policy zone requires the server to
            perform one to four additional database lookups before a
            query can be answered.
            For example, a DNS server with four policy zones, each with all
            four kinds of response triggers, QNAME, IP, NSIP, and
            NSDNAME, requires a total of 17 times as many database
            lookups as a similar DNS server with no response policy zones.
            A <acronym class="acronym">BIND9</acronym> server with adequate memory and one
            response policy zone with QNAME and IP triggers might achieve a
            maximum queries-per-second rate about 20% lower.
            A server with four response policy zones with QNAME and IP
            triggers might have a maximum QPS rate about 50% lower.
          </p>
<p>
            Responses rewritten by RPZ are counted in the
            <span><strong class="command">RPZRewrites</strong></span> statistics.
          </p>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2589264"></a>Response Rate Limiting</h4></div></div></div>
<p>
            This feature is only available when <acronym class="acronym">BIND</acronym> 9
            is compiled with the <strong class="userinput"><code>--enable-rrl</code></strong>
            option on the "configure" command line.
          </p>
<p>
            Excessive almost identical UDP <span class="emphasis"><em>responses</em></span>
            can be controlled by configuring a
            <span><strong class="command">rate-limit</strong></span> clause in an
            <span><strong class="command">options</strong></span> or <span><strong class="command">view</strong></span> statement.
            This mechanism keeps authoritative BIND 9 from being used
            in amplifying reflection denial of service (DoS) attacks.
            Short truncated (TC=1) responses can be sent to provide
            rate-limited responses to legitimate clients within
            a range of forged, attacked IP addresses.
            Legitimate clients react to dropped or truncated response
            by retrying with UDP or with TCP respectively.
          </p>
<p>
            This mechanism is intended for authoritative DNS servers.
            It can be used on recursive servers but can slow
            applications such as SMTP servers (mail receivers) and
            HTTP clients (web browsers) that repeatedly request the
            same domains.
            When possible, closing "open" recursive servers is better.
          </p>
<p>
            Response rate limiting uses a "credit" or "token bucket" scheme.
            Each combination of identical response and client
            has a conceptual account that earns a specified number
            of credits every second.
            A prospective response debits its account by one.
            Responses are dropped or truncated
            while the account is negative.
            Responses are tracked within a rolling window of time
            which defaults to 15 seconds, but can be configured with
            the <span><strong class="command">window</strong></span> option to any value from
            1 to 3600 seconds (1 hour).
            The account cannot become more positive than
            the per-second limit
            or more negative than <span><strong class="command">window</strong></span>
            times the per-second limit.
            When the specified number of credits for a class of
            responses is set to 0, those responses are not rate limited.
          </p>
<p>
            The notions of "identical response" and "DNS client"
            for rate limiting are not simplistic.
            All responses to an address block are counted as if to a
            single client.
            The prefix lengths of addresses blocks are
            specified with <span><strong class="command">ipv4-prefix-length</strong></span> (default 24)
            and <span><strong class="command">ipv6-prefix-length</strong></span> (default 56).
          </p>
<p>
            All non-empty responses for a valid domain name (qname)
            and record type (qtype) are identical and have a limit specified
            with <span><strong class="command">responses-per-second</strong></span>
            (default 0 or no limit).
            All empty (NODATA) responses for a valid domain,
            regardless of query type, are identical.
            Responses in the NODATA class are limited by
            <span><strong class="command">nodata-per-second</strong></span>
            (default <span><strong class="command">responses-per-second</strong></span>).
            Requests for any and all undefined subdomains of a given
            valid domain result in NXDOMAIN errors, and are identical
            regardless of query type.
            They are limited by <span><strong class="command">nxdomain-per-second</strong></span>
            (default <span><strong class="command">responses-per-second</strong></span>).
            This controls some attacks using random names, but
            can be relaxed or turned off (set to 0)
            on servers that expect many legitimate
            NXDOMAIN responses, such as from anti-spam blacklists.
            Referrals or delegations to the server of a given
            domain are identical and are limited by
            <span><strong class="command">referrals-per-second</strong></span>
            (default <span><strong class="command">responses-per-second</strong></span>).
          </p>
<p>
            Responses generated from local wildcards are counted and limited
            as if they were for the parent domain name.
            This controls flooding using random.wild.example.com.
          </p>
<p>
            All requests that result in DNS errors other
            than NXDOMAIN, such as SERVFAIL and FORMERR, are identical
            regardless of requested name (qname) or record type (qtype).
            This controls attacks using invalid requests or distant,
            broken authoritative servers.
            By default the limit on errors is the same as the
            <span><strong class="command">responses-per-second</strong></span> value,
            but it can be set separately with
            <span><strong class="command">errors-per-second</strong></span>.
          </p>
<p>
            Many attacks using DNS involve UDP requests with forged source
            addresses.
            Rate limiting prevents the use of BIND 9 to flood a network
            with responses to requests with forged source addresses,
            but could let a third party block responses to legitimate requests.
            There is a mechanism that can answer some legitimate
            requests from a client whose address is being forged in a flood.
            Setting <span><strong class="command">slip</strong></span> to 2 (its default) causes every
            other UDP request to be answered with a small truncated (TC=1)
            response.
            The small size and reduced frequency, and so lack of
            amplification, of "slipped" responses make them unattractive
            for reflection DoS attacks.
            <span><strong class="command">slip</strong></span> must be between 0 and 10.
            A value of 0 does not "slip":
            no truncated responses are sent due to rate limiting,
            all responses are dropped.
            A value of 1 causes every response to slip;
            values between 2 and 10 cause every n'th response to slip.
            Some error responses including REFUSED and SERVFAIL
            cannot be replaced with truncated responses and are instead
            leaked at the <span><strong class="command">slip</strong></span> rate.
          </p>
<p>
            (NOTE: Dropped responses from an authoritative server may
            reduce the difficulty of a third party successfully forging
            a response to a recursive resolver. The best security
            against forged responses is for authoritative operators
            to sign their zones using DNSSEC and for resolver operators
            to validate the responses. When this is not an option,
            operators who are more concerned with response integrity
            than with flood mitigation may consider setting
            <span><strong class="command">slip</strong></span> to 1, causing all rate-limited
            responses to be truncated rather than dropped.  This reduces
            the effectiveness of rate-limiting against reflection attacks.)
          </p>
<p>
            When the approximate query per second rate exceeds
            the <span><strong class="command">qps-scale</strong></span> value,
            then the <span><strong class="command">responses-per-second</strong></span>,
            <span><strong class="command">errors-per-second</strong></span>,
            <span><strong class="command">nxdomains-per-second</strong></span> and
            <span><strong class="command">all-per-second</strong></span> values are reduced by the
            ratio of the current rate to the <span><strong class="command">qps-scale</strong></span> value.
            This feature can tighten defenses during attacks.
            For example, with
            <span><strong class="command">qps-scale 250; responses-per-second 20;</strong></span> and
            a total query rate of 1000 queries/second for all queries from
            all DNS clients including via TCP,
            then the effective responses/second limit changes to
            (250/1000)*20 or 5.
            Responses sent via TCP are not limited
            but are counted to compute the query per second rate.
          </p>
<p>
            Communities of DNS clients can be given their own parameters or no
            rate limiting by putting
            <span><strong class="command">rate-limit</strong></span> statements in <span><strong class="command">view</strong></span>
            statements instead of the global <span><strong class="command">option</strong></span>
            statement.
            A <span><strong class="command">rate-limit</strong></span> statement in a view replaces,
            rather than supplementing, a <span><strong class="command">rate-limit</strong></span>
            statement among the main options.
            DNS clients within a view can be exempted from rate limits
            with the <span><strong class="command">exempt-clients</strong></span> clause.
          </p>
<p>
            UDP responses of all kinds can be limited with the
            <span><strong class="command">all-per-second</strong></span> phrase.
            This rate limiting is unlike the rate limiting provided by
            <span><strong class="command">responses-per-second</strong></span>,
            <span><strong class="command">errors-per-second</strong></span>, and
            <span><strong class="command">nxdomains-per-second</strong></span> on a DNS server
            which are often invisible to the victim of a DNS reflection attack.
            Unless the forged requests of the attack are the same as the
            legitimate requests of the victim, the victim's requests are
            not affected.
            Responses affected by an <span><strong class="command">all-per-second</strong></span> limit
            are always dropped; the <span><strong class="command">slip</strong></span> value has no
            effect.
            An <span><strong class="command">all-per-second</strong></span> limit should be
            at least 4 times as large as the other limits,
            because single DNS clients often send bursts of legitimate
            requests.
            For example, the receipt of a single mail message can prompt
            requests from an SMTP server for NS, PTR, A, and AAAA records
            as the incoming SMTP/TCP/IP connection is considered.
            The SMTP server can need additional NS, A, AAAA, MX, TXT, and SPF
            records as it considers the STMP <span><strong class="command">Mail From</strong></span>
            command.
            Web browsers often repeatedly resolve the same names that
            are repeated in HTML &lt;IMG&gt; tags in a page.
            <span><strong class="command">All-per-second</strong></span> is similar to the
            rate limiting offered by firewalls but often inferior.
            Attacks that justify ignoring the
            contents of DNS responses are likely to be attacks on the
            DNS server itself.
            They usually should be discarded before the DNS server
            spends resources making TCP connections or parsing DNS requests,
            but that rate limiting must be done before the
            DNS server sees the requests.
          </p>
<p>
            The maximum size of the table used to track requests and
            rate limit responses is set with <span><strong class="command">max-table-size</strong></span>.
            Each entry in the table is between 40 and 80 bytes.
            The table needs approximately as many entries as the number
            of requests received per second.
            The default is 20,000.
            To reduce the cold start of growing the table,
            <span><strong class="command">min-table-size</strong></span> (default 500)
            can set the minimum table size.
            Enable <span><strong class="command">rate-limit</strong></span> category logging to monitor
            expansions of the table and inform
            choices for the initial and maximum table size.
          </p>
<p>
            Use <span><strong class="command">log-only yes</strong></span> to test rate limiting parameters
            without actually dropping any requests.
          </p>
<p>
            Responses dropped by rate limits are included in the
            <span><strong class="command">RateDropped</strong></span> and <span><strong class="command">QryDropped</strong></span>
            statistics.
            Responses that truncated by rate limits are included in
            <span><strong class="command">RateSlipped</strong></span> and <span><strong class="command">RespTruncated</strong></span>.
          </p>
</div>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="server_statement_grammar"></a><span><strong class="command">server</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span><strong class="command">server</strong></span> <em class="replaceable"><code>ip_addr[/prefixlen]</code></em> {
    [<span class="optional"> bogus <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> provide-ixfr <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> request-ixfr <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> request-nsid <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> edns <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> edns-udp-size <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-udp-size <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> transfers <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> transfer-format <em class="replaceable"><code>( one-answer | many-answers )</code></em> ; ]</span>]
    [<span class="optional"> keys <em class="replaceable"><code>{ string ; [<span class="optional"> string ; [<span class="optional">...</span>]</span>] }</code></em> ; </span>]
    [<span class="optional"> transfer-source (<em class="replaceable"><code>ip4_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> transfer-source-v6 (<em class="replaceable"><code>ip6_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> notify-source (<em class="replaceable"><code>ip4_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> notify-source-v6 (<em class="replaceable"><code>ip6_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> query-source [<span class="optional"> address ( <em class="replaceable"><code>ip_addr</code></em> | <em class="replaceable"><code>*</code></em> ) </span>]
                  [<span class="optional"> port ( <em class="replaceable"><code>ip_port</code></em> | <em class="replaceable"><code>*</code></em> ) </span>]; </span>]
    [<span class="optional"> query-source-v6 [<span class="optional"> address ( <em class="replaceable"><code>ip_addr</code></em> | <em class="replaceable"><code>*</code></em> ) </span>]
                     [<span class="optional"> port ( <em class="replaceable"><code>ip_port</code></em> | <em class="replaceable"><code>*</code></em> ) </span>]; </span>]
    [<span class="optional"> use-queryport-pool <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> queryport-pool-ports <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> queryport-pool-updateinterval <em class="replaceable"><code>number</code></em>; </span>]
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="server_statement_definition_and_usage"></a><span><strong class="command">server</strong></span> Statement Definition and
            Usage</h3></div></div></div>
<p>
            The <span><strong class="command">server</strong></span> statement defines
            characteristics
            to be associated with a remote name server.  If a prefix length is
            specified, then a range of servers is covered.  Only the most
            specific
            server clause applies regardless of the order in
            <code class="filename">named.conf</code>.
          </p>
<p>
            The <span><strong class="command">server</strong></span> statement can occur at
            the top level of the
            configuration file or inside a <span><strong class="command">view</strong></span>
            statement.
            If a <span><strong class="command">view</strong></span> statement contains
            one or more <span><strong class="command">server</strong></span> statements, only
            those
            apply to the view and any top-level ones are ignored.
            If a view contains no <span><strong class="command">server</strong></span>
            statements,
            any top-level <span><strong class="command">server</strong></span> statements are
            used as
            defaults.
          </p>
<p>
            If you discover that a remote server is giving out bad data,
            marking it as bogus will prevent further queries to it. The
            default
            value of <span><strong class="command">bogus</strong></span> is <span><strong class="command">no</strong></span>.
          </p>
<p>
            The <span><strong class="command">provide-ixfr</strong></span> clause determines
            whether
            the local server, acting as master, will respond with an
            incremental
            zone transfer when the given remote server, a slave, requests it.
            If set to <span><strong class="command">yes</strong></span>, incremental transfer
            will be provided
            whenever possible. If set to <span><strong class="command">no</strong></span>,
            all transfers
            to the remote server will be non-incremental. If not set, the
            value
            of the <span><strong class="command">provide-ixfr</strong></span> option in the
            view or
            global options block is used as a default.
          </p>
<p>
            The <span><strong class="command">request-ixfr</strong></span> clause determines
            whether
            the local server, acting as a slave, will request incremental zone
            transfers from the given remote server, a master. If not set, the
            value of the <span><strong class="command">request-ixfr</strong></span> option in
            the view or global options block is used as a default. It may
            also be set in the zone block and, if set there, it will
            override the global or view setting for that zone.
          </p>
<p>
            IXFR requests to servers that do not support IXFR will
            automatically
            fall back to AXFR.  Therefore, there is no need to manually list
            which servers support IXFR and which ones do not; the global
            default
            of <span><strong class="command">yes</strong></span> should always work.
            The purpose of the <span><strong class="command">provide-ixfr</strong></span> and
            <span><strong class="command">request-ixfr</strong></span> clauses is
            to make it possible to disable the use of IXFR even when both
            master
            and slave claim to support it, for example if one of the servers
            is buggy and crashes or corrupts data when IXFR is used.
          </p>
<p>
            The <span><strong class="command">edns</strong></span> clause determines whether
            the local server will attempt to use EDNS when communicating
            with the remote server.  The default is <span><strong class="command">yes</strong></span>.
          </p>
<p>
            The <span><strong class="command">edns-udp-size</strong></span> option sets the EDNS UDP size
            that is advertised by <span><strong class="command">named</strong></span> when querying the remote server.
            Valid values are 512 to 4096 bytes (values outside this range will be
            silently adjusted).  This option is useful when you wish to
            advertises a different value to this server than the value you
            advertise globally, for example, when there is a firewall at the
            remote site that is blocking large replies.
          </p>
<p>
            The <span><strong class="command">max-udp-size</strong></span> option sets the
            maximum EDNS UDP message size <span><strong class="command">named</strong></span> will send.  Valid
            values are 512 to 4096 bytes (values outside this range will
            be silently adjusted).  This option is useful when you
            know that there is a firewall that is blocking large
            replies from <span><strong class="command">named</strong></span>.
          </p>
<p>
            The server supports two zone transfer methods. The first, <span><strong class="command">one-answer</strong></span>,
            uses one DNS message per resource record transferred. <span><strong class="command">many-answers</strong></span> packs
            as many resource records as possible into a message. <span><strong class="command">many-answers</strong></span> is
            more efficient, but is only known to be understood by <acronym class="acronym">BIND</acronym> 9, <acronym class="acronym">BIND</acronym>
            8.x, and patched versions of <acronym class="acronym">BIND</acronym>
            4.9.5. You can specify which method
            to use for a server with the <span><strong class="command">transfer-format</strong></span> option.
            If <span><strong class="command">transfer-format</strong></span> is not
            specified, the <span><strong class="command">transfer-format</strong></span>
            specified
            by the <span><strong class="command">options</strong></span> statement will be
            used.
          </p>
<p><span><strong class="command">transfers</strong></span>
            is used to limit the number of concurrent inbound zone
            transfers from the specified server. If no
            <span><strong class="command">transfers</strong></span> clause is specified, the
            limit is set according to the
            <span><strong class="command">transfers-per-ns</strong></span> option.
          </p>
<p>
            The <span><strong class="command">keys</strong></span> clause identifies a
            <span><strong class="command">key_id</strong></span> defined by the <span><strong class="command">key</strong></span> statement,
            to be used for transaction security (TSIG, <a href="Bv9ARM.ch04.html#tsig" title="TSIG">the section called &#8220;TSIG&#8221;</a>)
            when talking to the remote server.
            When a request is sent to the remote server, a request signature
            will be generated using the key specified here and appended to the
            message. A request originating from the remote server is not
            required
            to be signed by this key.
          </p>
<p>
            Although the grammar of the <span><strong class="command">keys</strong></span>
            clause
            allows for multiple keys, only a single key per server is
            currently
            supported.
          </p>
<p>
            The <span><strong class="command">transfer-source</strong></span> and
            <span><strong class="command">transfer-source-v6</strong></span> clauses specify
            the IPv4 and IPv6 source
            address to be used for zone transfer with the remote server,
            respectively.
            For an IPv4 remote server, only <span><strong class="command">transfer-source</strong></span> can
            be specified.
            Similarly, for an IPv6 remote server, only
            <span><strong class="command">transfer-source-v6</strong></span> can be
            specified.
            For more details, see the description of
            <span><strong class="command">transfer-source</strong></span> and
            <span><strong class="command">transfer-source-v6</strong></span> in
            <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
          </p>
<p>
            The <span><strong class="command">notify-source</strong></span> and
            <span><strong class="command">notify-source-v6</strong></span> clauses specify the
            IPv4 and IPv6 source address to be used for notify
            messages sent to remote servers, respectively.  For an
            IPv4 remote server, only <span><strong class="command">notify-source</strong></span>
            can be specified.  Similarly, for an IPv6 remote server,
            only <span><strong class="command">notify-source-v6</strong></span> can be specified.
          </p>
<p>
            The <span><strong class="command">query-source</strong></span> and
            <span><strong class="command">query-source-v6</strong></span> clauses specify the
            IPv4 and IPv6 source address to be used for queries
            sent to remote servers, respectively.  For an IPv4
            remote server, only <span><strong class="command">query-source</strong></span> can
            be specified.  Similarly, for an IPv6 remote server,
            only <span><strong class="command">query-source-v6</strong></span> can be specified.
          </p>
<p>
            The <span><strong class="command">request-nsid</strong></span> clause determines
            whether the local server will add a NSID EDNS option
            to requests sent to the server.  This overrides
            <span><strong class="command">request-nsid</strong></span> set at the view or
            option level. 
          </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="statschannels"></a><span><strong class="command">statistics-channels</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span><strong class="command">statistics-channels</strong></span> {
   [ inet ( ip_addr | * ) [ port ip_port ]
   [ allow { <em class="replaceable"><code> address_match_list </code></em> } ]; ]
   [ inet ...; ]
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2590489"></a><span><strong class="command">statistics-channels</strong></span> Statement Definition and
            Usage</h3></div></div></div>
<p>
          The <span><strong class="command">statistics-channels</strong></span> statement
          declares communication channels to be used by system
          administrators to get access to statistics information of
          the name server.
        </p>
<p>
          This statement intends to be flexible to support multiple
          communication protocols in the future, but currently only
          HTTP access is supported.
          It requires that BIND 9 be compiled with libxml2;
          the <span><strong class="command">statistics-channels</strong></span> statement is
          still accepted even if it is built without the library,
          but any HTTP access will fail with an error.
        </p>
<p>
          An <span><strong class="command">inet</strong></span> control channel is a TCP socket
          listening at the specified <span><strong class="command">ip_port</strong></span> on the
          specified <span><strong class="command">ip_addr</strong></span>, which can be an IPv4 or IPv6
          address.  An <span><strong class="command">ip_addr</strong></span> of <code class="literal">*</code> (asterisk) is
          interpreted as the IPv4 wildcard address; connections will be
          accepted on any of the system's IPv4 addresses.
          To listen on the IPv6 wildcard address,
          use an <span><strong class="command">ip_addr</strong></span> of <code class="literal">::</code>.
        </p>
<p>
          If no port is specified, port 80 is used for HTTP channels.
          The asterisk "<code class="literal">*</code>" cannot be used for
          <span><strong class="command">ip_port</strong></span>.
        </p>
<p>
          The attempt of opening a statistics channel is
          restricted by the optional <span><strong class="command">allow</strong></span> clause.
          Connections to the statistics channel are permitted based on the
          <span><strong class="command">address_match_list</strong></span>.
          If no <span><strong class="command">allow</strong></span> clause is present,
          <span><strong class="command">named</strong></span> accepts connection
          attempts from any address; since the statistics may
          contain sensitive internal information, it is highly
          recommended to restrict the source of connection requests
          appropriately.
        </p>
<p>
          If no <span><strong class="command">statistics-channels</strong></span> statement is present,
          <span><strong class="command">named</strong></span> will not open any communication channels.
        </p>
<p>
          If the statistics channel is configured to listen on 127.0.0.1
          port 8888, then the statistics are accessible in XML format at
          <a href="http://127.0.0.1:8888/" target="_top">http://127.0.0.1:8888/</a> or
          <a href="http://127.0.0.1:8888/xml" target="_top">http://127.0.0.1:8888/xml</a>. A CSS file is
          included which can format the XML statistics into tables 
          when viewed with a stylesheet-capable browser.  When
          <acronym class="acronym">BIND</acronym> 9 is configured with --enable-newstats, 
          a new XML schema is used (version 3) which adds additional
          zone statistics and uses a flatter tree for more efficient
          parsing.  The stylesheet included uses the Google Charts API
          to render data into into charts and graphs when using a
          javascript-capable browser.
        </p>
<p>
          Applications that depend on a particular XML schema
          can request 
          <a href="http://127.0.0.1:8888/xml/v2" target="_top">http://127.0.0.1:8888/xml/v2</a> for version 2
          of the statistics XML schema or 
          <a href="http://127.0.0.1:8888/xml/v3" target="_top">http://127.0.0.1:8888/xml/v3</a> for version 3.
          If the requested schema is supported by the server, then
          it will respond; if not, it will return a "page not found"
          error.
        </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="trusted-keys"></a><span><strong class="command">trusted-keys</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span><strong class="command">trusted-keys</strong></span> {
    <em class="replaceable"><code>string</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>string</code></em> ;
    [<span class="optional"> <em class="replaceable"><code>string</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>string</code></em> ; [<span class="optional">...</span>]</span>]
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2590796"></a><span><strong class="command">trusted-keys</strong></span> Statement Definition
            and Usage</h3></div></div></div>
<p>
            The <span><strong class="command">trusted-keys</strong></span> statement defines
            DNSSEC security roots. DNSSEC is described in <a href="Bv9ARM.ch04.html#DNSSEC" title="DNSSEC">the section called &#8220;DNSSEC&#8221;</a>. A security root is defined when the
            public key for a non-authoritative zone is known, but
            cannot be securely obtained through DNS, either because
            it is the DNS root zone or because its parent zone is
            unsigned.  Once a key has been configured as a trusted
            key, it is treated as if it had been validated and
            proven secure. The resolver attempts DNSSEC validation
            on all DNS data in subdomains of a security root.
          </p>
<p>
            All keys (and corresponding zones) listed in
            <span><strong class="command">trusted-keys</strong></span> are deemed to exist regardless
            of what parent zones say.  Similarly for all keys listed in
            <span><strong class="command">trusted-keys</strong></span> only those keys are
            used to validate the DNSKEY RRset.  The parent's DS RRset
            will not be used.
          </p>
<p>
            The <span><strong class="command">trusted-keys</strong></span> statement can contain
            multiple key entries, each consisting of the key's
            domain name, flags, protocol, algorithm, and the Base-64
            representation of the key data.
            Spaces, tabs, newlines and carriage returns are ignored
            in the key data, so the configuration may be split up into
            multiple lines.
          </p>
<p>
            <span><strong class="command">trusted-keys</strong></span> may be set at the top level
            of <code class="filename">named.conf</code> or within a view.  If it is
            set in both places, they are additive: keys defined at the top
            level are inherited by all views, but keys defined in a view
            are only used within that view.
          </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2590843"></a><span><strong class="command">managed-keys</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span><strong class="command">managed-keys</strong></span> {
    <em class="replaceable"><code>name</code></em> initial-key <em class="replaceable"><code>flags</code></em> <em class="replaceable"><code>protocol</code></em> <em class="replaceable"><code>algorithm</code></em> <em class="replaceable"><code>key-data</code></em> ;
    [<span class="optional"> <em class="replaceable"><code>name</code></em> initial-key <em class="replaceable"><code>flags</code></em> <em class="replaceable"><code>protocol</code></em> <em class="replaceable"><code>algorithm</code></em> <em class="replaceable"><code>key-data</code></em> ; [<span class="optional">...</span>]</span>]
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="managed-keys"></a><span><strong class="command">managed-keys</strong></span> Statement Definition
            and Usage</h3></div></div></div>
<p>
            The <span><strong class="command">managed-keys</strong></span> statement, like 
            <span><strong class="command">trusted-keys</strong></span>, defines DNSSEC
            security roots.  The difference is that
            <span><strong class="command">managed-keys</strong></span> can be kept up to date
            automatically, without intervention from the resolver
            operator.
          </p>
<p>
            Suppose, for example, that a zone's key-signing
            key was compromised, and the zone owner had to revoke and
            replace the key.  A resolver which had the old key in a
            <span><strong class="command">trusted-keys</strong></span> statement would be
            unable to validate this zone any longer; it would
            reply with a SERVFAIL response code.  This would
            continue until the resolver operator had updated the
            <span><strong class="command">trusted-keys</strong></span> statement with the new key.
          </p>
<p>
            If, however, the zone were listed in a
            <span><strong class="command">managed-keys</strong></span> statement instead, then the
            zone owner could add a "stand-by" key to the zone in advance.
            <span><strong class="command">named</strong></span> would store the stand-by key, and
            when the original key was revoked, <span><strong class="command">named</strong></span>
            would be able to transition smoothly to the new key.  It would
            also recognize that the old key had been revoked, and cease
            using that key to validate answers, minimizing the damage that
            the compromised key could do.
          </p>
<p>
            A <span><strong class="command">managed-keys</strong></span> statement contains a list of
            the keys to be managed, along with information about how the
            keys are to be initialized for the first time.  The only
            initialization method currently supported (as of
            <acronym class="acronym">BIND</acronym> 9.7.0) is <code class="literal">initial-key</code>.
            This means the <span><strong class="command">managed-keys</strong></span> statement must
            contain a copy of the initializing key.  (Future releases may
            allow keys to be initialized by other methods, eliminating this
            requirement.)
          </p>
<p>
            Consequently, a <span><strong class="command">managed-keys</strong></span> statement
            appears similar to a <span><strong class="command">trusted-keys</strong></span>, differing
            in the presence of the second field, containing the keyword
            <code class="literal">initial-key</code>.  The difference is, whereas the
            keys listed in a <span><strong class="command">trusted-keys</strong></span> continue to be
            trusted until they are removed from
            <code class="filename">named.conf</code>, an initializing key listed 
            in a <span><strong class="command">managed-keys</strong></span> statement is only trusted
            <span class="emphasis"><em>once</em></span>: for as long as it takes to load the
            managed key database and start the RFC 5011 key maintenance
            process.
          </p>
<p>
            The first time <span><strong class="command">named</strong></span> runs with a managed key
            configured in <code class="filename">named.conf</code>, it fetches the
            DNSKEY RRset directly from the zone apex, and validates it
            using the key specified in the <span><strong class="command">managed-keys</strong></span>
            statement.  If the DNSKEY RRset is validly signed, then it is
            used as the basis for a new managed keys database.
          </p>
<p>
            From that point on, whenever <span><strong class="command">named</strong></span> runs, it
            sees the <span><strong class="command">managed-keys</strong></span> statement, checks to
            make sure RFC 5011 key maintenance has already been initialized
            for the specified domain, and if so, it simply moves on.  The
            key specified in the <span><strong class="command">managed-keys</strong></span> is not
            used to validate answers; it has been superseded by the key or
            keys stored in the managed keys database.
          </p>
<p>
            The next time <span><strong class="command">named</strong></span> runs after a name
            has been <span class="emphasis"><em>removed</em></span> from the
            <span><strong class="command">managed-keys</strong></span> statement, the corresponding
            zone will be removed from the managed keys database,
            and RFC 5011 key maintenance will no longer be used for that
            domain.
          </p>
<p>
            <span><strong class="command">named</strong></span> only maintains a single managed keys
            database; consequently, unlike <span><strong class="command">trusted-keys</strong></span>,
            <span><strong class="command">managed-keys</strong></span> may only be set at the top
            level of <code class="filename">named.conf</code>, not within a view.
          </p>
<p>
            In the current implementation, the managed keys database is
            stored as a master-format zone file called
            <code class="filename">managed-keys.bind</code>.  When the key database
            is changed, the zone is updated.  As with any other dynamic
            zone, changes will be written into a journal file,
            <code class="filename">managed-keys.bind.jnl</code>.  They are committed
            to the master file as soon as possible afterward; in the case
            of the managed key database, this will usually occur within 30
            seconds.  So, whenever <span><strong class="command">named</strong></span> is using
            automatic key maintenance, those two files can be expected to
            exist in the working directory.  (For this reason among others,
            the working directory should be always be writable by
            <span><strong class="command">named</strong></span>.)
          </p>
<p>
            If the <span><strong class="command">dnssec-validation</strong></span> option is
            set to <strong class="userinput"><code>auto</code></strong>, <span><strong class="command">named</strong></span>
            will automatically initialize a managed key for the
            root zone.  Similarly, if the <span><strong class="command">dnssec-lookaside</strong></span>
            option is set to <strong class="userinput"><code>auto</code></strong>,
            <span><strong class="command">named</strong></span> will automatically initialize
            a managed key for the zone <code class="literal">dlv.isc.org</code>.
            In both cases, the key that is used to initialize the key
            maintenance process is built into <span><strong class="command">named</strong></span>,
            and can be overridden from <span><strong class="command">bindkeys-file</strong></span>.
          </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="view_statement_grammar"></a><span><strong class="command">view</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span><strong class="command">view</strong></span> <em class="replaceable"><code>view_name</code></em>
      [<span class="optional"><em class="replaceable"><code>class</code></em></span>] {
      match-clients { <em class="replaceable"><code>address_match_list</code></em> };
      match-destinations { <em class="replaceable"><code>address_match_list</code></em> };
      match-recursive-only <em class="replaceable"><code>yes_or_no</code></em> ;
      [<span class="optional"> <em class="replaceable"><code>view_option</code></em>; ...</span>]
      [<span class="optional"> <em class="replaceable"><code>zone_statement</code></em>; ...</span>]
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2591278"></a><span><strong class="command">view</strong></span> Statement Definition and Usage</h3></div></div></div>
<p>
            The <span><strong class="command">view</strong></span> statement is a powerful
            feature
            of <acronym class="acronym">BIND</acronym> 9 that lets a name server
            answer a DNS query differently
            depending on who is asking. It is particularly useful for
            implementing
            split DNS setups without having to run multiple servers.
          </p>
<p>
            Each <span><strong class="command">view</strong></span> statement defines a view
            of the
            DNS namespace that will be seen by a subset of clients.  A client
            matches
            a view if its source IP address matches the
            <code class="varname">address_match_list</code> of the view's
            <span><strong class="command">match-clients</strong></span> clause and its
            destination IP address matches
            the <code class="varname">address_match_list</code> of the
            view's
            <span><strong class="command">match-destinations</strong></span> clause.  If not
            specified, both
            <span><strong class="command">match-clients</strong></span> and <span><strong class="command">match-destinations</strong></span>
            default to matching all addresses.  In addition to checking IP
            addresses
            <span><strong class="command">match-clients</strong></span> and <span><strong class="command">match-destinations</strong></span>
            can also take <span><strong class="command">keys</strong></span> which provide an
            mechanism for the
            client to select the view.  A view can also be specified
            as <span><strong class="command">match-recursive-only</strong></span>, which
            means that only recursive
            requests from matching clients will match that view.
            The order of the <span><strong class="command">view</strong></span> statements is
            significant &#8212;
            a client request will be resolved in the context of the first
            <span><strong class="command">view</strong></span> that it matches.
          </p>
<p>
            Zones defined within a <span><strong class="command">view</strong></span>
            statement will
            only be accessible to clients that match the <span><strong class="command">view</strong></span>.
            By defining a zone of the same name in multiple views, different
            zone data can be given to different clients, for example,
            "internal"
            and "external" clients in a split DNS setup.
          </p>
<p>
            Many of the options given in the <span><strong class="command">options</strong></span> statement
            can also be used within a <span><strong class="command">view</strong></span>
            statement, and then
            apply only when resolving queries with that view.  When no
            view-specific
            value is given, the value in the <span><strong class="command">options</strong></span> statement
            is used as a default.  Also, zone options can have default values
            specified
            in the <span><strong class="command">view</strong></span> statement; these
            view-specific defaults
            take precedence over those in the <span><strong class="command">options</strong></span> statement.
          </p>
<p>
            Views are class specific.  If no class is given, class IN
            is assumed.  Note that all non-IN views must contain a hint zone,
            since only the IN class has compiled-in default hints.
          </p>
<p>
            If there are no <span><strong class="command">view</strong></span> statements in
            the config
            file, a default view that matches any client is automatically
            created
            in class IN. Any <span><strong class="command">zone</strong></span> statements
            specified on
            the top level of the configuration file are considered to be part
            of
            this default view, and the <span><strong class="command">options</strong></span>
            statement will
            apply to the default view. If any explicit <span><strong class="command">view</strong></span>
            statements are present, all <span><strong class="command">zone</strong></span>
            statements must
            occur inside <span><strong class="command">view</strong></span> statements.
          </p>
<p>
            Here is an example of a typical split DNS setup implemented
            using <span><strong class="command">view</strong></span> statements:
          </p>
<pre class="programlisting">view "internal" {
      // This should match our internal networks.
      match-clients { 10.0.0.0/8; };

      // Provide recursive service to internal
      // clients only.
      recursion yes;

      // Provide a complete view of the example.com
      // zone including addresses of internal hosts.
      zone "example.com" {
            type master;
            file "example-internal.db";
      };
};

view "external" {
      // Match all clients not matched by the
      // previous view.
      match-clients { any; };

      // Refuse recursive service to external clients.
      recursion no;

      // Provide a restricted view of the example.com
      // zone containing only publicly accessible hosts.
      zone "example.com" {
           type master;
           file "example-external.db";
      };
};
</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="zone_statement_grammar"></a><span><strong class="command">zone</strong></span>
            Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span><strong class="command">zone</strong></span> <em class="replaceable"><code>zone_name</code></em> [<span class="optional"><em class="replaceable"><code>class</code></em></span>] {
    type master;
    [<span class="optional"> allow-query { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-query-on { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-transfer { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-update { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> update-check-ksk <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> dnssec-dnskey-kskonly <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> dnssec-loadkeys-interval <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> update-policy <em class="replaceable"><code>local</code></em> | { <em class="replaceable"><code>update_policy_rule</code></em> [<span class="optional">...</span>] }; </span>]
    [<span class="optional"> also-notify { <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ;
                  [<span class="optional"> <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; ... </span>] }; </span>]
    [<span class="optional"> check-names (<code class="constant">warn</code>|<code class="constant">fail</code>|<code class="constant">ignore</code>) ; </span>]
    [<span class="optional"> check-mx (<code class="constant">warn</code>|<code class="constant">fail</code>|<code class="constant">ignore</code>) ; </span>]
    [<span class="optional"> check-wildcard <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> check-spf ( <em class="replaceable"><code>warn</code></em> | <em class="replaceable"><code>ignore</code></em> ); </span>]
    [<span class="optional"> check-integrity <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> dialup <em class="replaceable"><code>dialup_option</code></em> ; </span>]
    [<span class="optional"> file <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> masterfile-format (<code class="constant">text</code>|<code class="constant">raw</code>) ; </span>]
    [<span class="optional"> journal <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> max-journal-size <em class="replaceable"><code>size_spec</code></em>; </span>]
    [<span class="optional"> forward (<code class="constant">only</code>|<code class="constant">first</code>) ; </span>]
    [<span class="optional"> forwarders { [<span class="optional"> <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; ... </span>] }; </span>]
    [<span class="optional"> ixfr-base <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> ixfr-from-differences <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> ixfr-tmp-file <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> request-ixfr <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> maintain-ixfr-base <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> max-ixfr-log-size <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-transfer-idle-out <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-transfer-time-out <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> notify <em class="replaceable"><code>yes_or_no</code></em> | <em class="replaceable"><code>explicit</code></em> | <em class="replaceable"><code>master-only</code></em> ; </span>]
    [<span class="optional"> notify-delay <em class="replaceable"><code>seconds</code></em> ; </span>]
    [<span class="optional"> notify-to-soa <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> pubkey <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> notify-source (<em class="replaceable"><code>ip4_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> notify-source-v6 (<em class="replaceable"><code>ip6_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> zone-statistics <em class="replaceable"><code>full</code></em> | <em class="replaceable"><code>terse</code></em> | <em class="replaceable"><code>none</code></em>; </span>]
    [<span class="optional"> sig-validity-interval <em class="replaceable"><code>number</code></em> [<span class="optional"><em class="replaceable"><code>number</code></em></span>] ; </span>]
    [<span class="optional"> sig-signing-nodes <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> sig-signing-signatures <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> sig-signing-type <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> database <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> min-refresh-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-refresh-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> min-retry-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-retry-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> key-directory <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> auto-dnssec <code class="constant">allow</code>|<code class="constant">maintain</code>|<code class="constant">off</code>; </span>]
    [<span class="optional"> inline-signing <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> zero-no-soa-ttl <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> serial-update-method <code class="constant">increment</code>|<code class="constant">unixtime</code>; </span>]
};

zone <em class="replaceable"><code>zone_name</code></em> [<span class="optional"><em class="replaceable"><code>class</code></em></span>] {
    type slave;
    [<span class="optional"> allow-notify { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-query { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-query-on { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-transfer { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-update-forwarding { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> dnssec-update-mode ( <em class="replaceable"><code>maintain</code></em> | <em class="replaceable"><code>no-resign</code></em> ); </span>]
    [<span class="optional"> update-check-ksk <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> dnssec-dnskey-kskonly <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> dnssec-loadkeys-interval <em class="replaceable"><code>number</code></em>; </span>]
    [<span class="optional"> dnssec-secure-to-insecure <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> try-tcp-refresh <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> also-notify [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] { ( <em class="replaceable"><code>masters_list</code></em> | <em class="replaceable"><code>ip_addr</code></em>
                              [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>]
                              [<span class="optional">key <em class="replaceable"><code>key</code></em></span>] ) ; [<span class="optional">...</span>] }; </span>]
    [<span class="optional"> check-names (<code class="constant">warn</code>|<code class="constant">fail</code>|<code class="constant">ignore</code>) ; </span>]
    [<span class="optional"> dialup <em class="replaceable"><code>dialup_option</code></em> ; </span>]
    [<span class="optional"> file <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> masterfile-format (<code class="constant">text</code>|<code class="constant">raw</code>) ; </span>]
    [<span class="optional"> journal <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> max-journal-size <em class="replaceable"><code>size_spec</code></em>; </span>]
    [<span class="optional"> forward (<code class="constant">only</code>|<code class="constant">first</code>) ; </span>]
    [<span class="optional"> forwarders { [<span class="optional"> <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; ... </span>] }; </span>]
    [<span class="optional"> ixfr-base <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> ixfr-from-differences <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> ixfr-tmp-file <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> maintain-ixfr-base <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> masters [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] { ( <em class="replaceable"><code>masters_list</code></em> | <em class="replaceable"><code>ip_addr</code></em>
                              [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>]
                              [<span class="optional">key <em class="replaceable"><code>key</code></em></span>] ) ; [<span class="optional">...</span>] }; </span>]
    [<span class="optional"> max-ixfr-log-size <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-transfer-idle-in <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-transfer-idle-out <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-transfer-time-in <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-transfer-time-out <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> notify <em class="replaceable"><code>yes_or_no</code></em> | <em class="replaceable"><code>explicit</code></em> | <em class="replaceable"><code>master-only</code></em> ; </span>]
    [<span class="optional"> notify-delay <em class="replaceable"><code>seconds</code></em> ; </span>]
    [<span class="optional"> notify-to-soa <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> pubkey <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> transfer-source (<em class="replaceable"><code>ip4_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> transfer-source-v6 (<em class="replaceable"><code>ip6_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> alt-transfer-source (<em class="replaceable"><code>ip4_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> alt-transfer-source-v6 (<em class="replaceable"><code>ip6_addr</code></em> | <code class="constant">*</code>)
                             [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> use-alt-transfer-source <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> notify-source (<em class="replaceable"><code>ip4_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> notify-source-v6 (<em class="replaceable"><code>ip6_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> zone-statistics <em class="replaceable"><code>full</code></em> | <em class="replaceable"><code>terse</code></em> | <em class="replaceable"><code>none</code></em>; </span>]
    [<span class="optional"> sig-validity-interval <em class="replaceable"><code>number</code></em> [<span class="optional"><em class="replaceable"><code>number</code></em></span>] ; </span>]
    [<span class="optional"> sig-signing-nodes <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> sig-signing-signatures <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> sig-signing-type <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> database <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> min-refresh-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-refresh-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> min-retry-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-retry-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> key-directory <em class="replaceable"><code>path_name</code></em>; </span>]
    [<span class="optional"> auto-dnssec <code class="constant">allow</code>|<code class="constant">maintain</code>|<code class="constant">off</code>; </span>]
    [<span class="optional"> inline-signing <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> multi-master <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> zero-no-soa-ttl <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
};

zone <em class="replaceable"><code>zone_name</code></em> [<span class="optional"><em class="replaceable"><code>class</code></em></span>] {
    type hint;
    file <em class="replaceable"><code>string</code></em> ;
    [<span class="optional"> delegation-only <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> check-names (<code class="constant">warn</code>|<code class="constant">fail</code>|<code class="constant">ignore</code>) ; </span>] // Not Implemented.
};

zone <em class="replaceable"><code>zone_name</code></em> [<span class="optional"><em class="replaceable"><code>class</code></em></span>] {
    type stub;
    [<span class="optional"> allow-query { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> allow-query-on { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> check-names (<code class="constant">warn</code>|<code class="constant">fail</code>|<code class="constant">ignore</code>) ; </span>]
    [<span class="optional"> dialup <em class="replaceable"><code>dialup_option</code></em> ; </span>]
    [<span class="optional"> delegation-only <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> file <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> masterfile-format (<code class="constant">text</code>|<code class="constant">raw</code>) ; </span>]
    [<span class="optional"> forward (<code class="constant">only</code>|<code class="constant">first</code>) ; </span>]
    [<span class="optional"> forwarders { [<span class="optional"> <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; ... </span>] }; </span>]
    [<span class="optional"> masters [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] { ( <em class="replaceable"><code>masters_list</code></em> | <em class="replaceable"><code>ip_addr</code></em>
                              [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>]
                              [<span class="optional">key <em class="replaceable"><code>key</code></em></span>] ) ; [<span class="optional">...</span>] }; </span>]
    [<span class="optional"> max-transfer-idle-in <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-transfer-time-in <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> pubkey <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>number</code></em> <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> transfer-source (<em class="replaceable"><code>ip4_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> transfer-source-v6 (<em class="replaceable"><code>ip6_addr</code></em> | <code class="constant">*</code>)
                         [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> alt-transfer-source (<em class="replaceable"><code>ip4_addr</code></em> | <code class="constant">*</code>) [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> alt-transfer-source-v6 (<em class="replaceable"><code>ip6_addr</code></em> | <code class="constant">*</code>)
                            [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; </span>]
    [<span class="optional"> use-alt-transfer-source <em class="replaceable"><code>yes_or_no</code></em>; </span>]
    [<span class="optional"> zone-statistics <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
    [<span class="optional"> database <em class="replaceable"><code>string</code></em> ; </span>]
    [<span class="optional"> min-refresh-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-refresh-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> min-retry-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> max-retry-time <em class="replaceable"><code>number</code></em> ; </span>]
    [<span class="optional"> multi-master <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
};

zone <em class="replaceable"><code>zone_name</code></em> [<span class="optional"><em class="replaceable"><code>class</code></em></span>] {
    type static-stub;
    [<span class="optional"> allow-query { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
    [<span class="optional"> server-addresses { [<span class="optional"> <em class="replaceable"><code>ip_addr</code></em> ; ... </span>] }; </span>]
    [<span class="optional"> server-names { [<span class="optional"> <em class="replaceable"><code>namelist</code></em> </span>] }; </span>]  
    [<span class="optional"> zone-statistics <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
};

zone <em class="replaceable"><code>zone_name</code></em> [<span class="optional"><em class="replaceable"><code>class</code></em></span>] {
    type forward;
    [<span class="optional"> forward (<code class="constant">only</code>|<code class="constant">first</code>) ; </span>]
    [<span class="optional"> forwarders { [<span class="optional"> <em class="replaceable"><code>ip_addr</code></em> [<span class="optional">port <em class="replaceable"><code>ip_port</code></em></span>] ; ... </span>] }; </span>]
    [<span class="optional"> delegation-only <em class="replaceable"><code>yes_or_no</code></em> ; </span>]
};

zone <em class="replaceable"><code>"."</code></em> [<span class="optional"><em class="replaceable"><code>class</code></em></span>] {
    type redirect;
    file <em class="replaceable"><code>string</code></em> ;
    [<span class="optional"> masterfile-format (<code class="constant">text</code>|<code class="constant">raw</code>) ; </span>]
    [<span class="optional"> allow-query { <em class="replaceable"><code>address_match_list</code></em> }; </span>]
};

zone <em class="replaceable"><code>zone_name</code></em> [<span class="optional"><em class="replaceable"><code>class</code></em></span>] {
    type delegation-only;
};

</pre>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2592987"></a><span><strong class="command">zone</strong></span> Statement Definition and Usage</h3></div></div></div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2592995"></a>Zone Types</h4></div></div></div>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                      <p>
                        <code class="varname">master</code>
                      </p>
                    </td>
<td>
                      <p>
                        The server has a master copy of the data
                        for the zone and will be able to provide authoritative
                        answers for
                        it.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">slave</code>
                      </p>
                    </td>
<td>
                      <p>
                        A slave zone is a replica of a master
                        zone. The <span><strong class="command">masters</strong></span> list
                        specifies one or more IP addresses
                        of master servers that the slave contacts to update
                        its copy of the zone.
                        Masters list elements can also be names of other
                        masters lists.
                        By default, transfers are made from port 53 on the
                        servers; this can
                        be changed for all servers by specifying a port number
                        before the
                        list of IP addresses, or on a per-server basis after
                        the IP address.
                        Authentication to the master can also be done with
                        per-server TSIG keys.
                        If a file is specified, then the
                        replica will be written to this file whenever the zone
                        is changed,
                        and reloaded from this file on a server restart. Use
                        of a file is
                        recommended, since it often speeds server startup and
                        eliminates
                        a needless waste of bandwidth. Note that for large
                        numbers (in the
                        tens or hundreds of thousands) of zones per server, it
                        is best to
                        use a two-level naming scheme for zone filenames. For
                        example,
                        a slave server for the zone <code class="literal">example.com</code> might place
                        the zone contents into a file called
                        <code class="filename">ex/example.com</code> where <code class="filename">ex/</code> is
                        just the first two letters of the zone name. (Most
                        operating systems
                        behave very slowly if you put 100000 files into
                        a single directory.)
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">stub</code>
                      </p>
                    </td>
<td>
                      <p>
                        A stub zone is similar to a slave zone,
                        except that it replicates only the NS records of a
                        master zone instead
                        of the entire zone. Stub zones are not a standard part
                        of the DNS;
                        they are a feature specific to the <acronym class="acronym">BIND</acronym> implementation.
                      </p>

                      <p>
                        Stub zones can be used to eliminate the need for glue
                        NS record
                        in a parent zone at the expense of maintaining a stub
                        zone entry and
                        a set of name server addresses in <code class="filename">named.conf</code>.
                        This usage is not recommended for new configurations,
                        and BIND 9
                        supports it only in a limited way.
                        In <acronym class="acronym">BIND</acronym> 4/8, zone
                        transfers of a parent zone
                        included the NS records from stub children of that
                        zone. This meant
                        that, in some cases, users could get away with
                        configuring child stubs
                        only in the master server for the parent zone. <acronym class="acronym">BIND</acronym>
                        9 never mixes together zone data from different zones
                        in this
                        way. Therefore, if a <acronym class="acronym">BIND</acronym> 9 master serving a parent
                        zone has child stub zones configured, all the slave
                        servers for the
                        parent zone also need to have the same child stub
                        zones
                        configured.
                      </p>

                      <p>
                        Stub zones can also be used as a way of forcing the
                        resolution
                        of a given domain to use a particular set of
                        authoritative servers.
                        For example, the caching name servers on a private
                        network using
                        RFC1918 addressing may be configured with stub zones
                        for
                        <code class="literal">10.in-addr.arpa</code>
                        to use a set of internal name servers as the
                        authoritative
                        servers for that domain.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">static-stub</code>
                      </p>
                    </td>
<td>
                      <p>
                        A static-stub zone is similar to a stub zone
                        with the following exceptions:
                        the zone data is statically configured, rather
                        than transferred from a master server;
                        when recursion is necessary for a query that
                        matches a static-stub zone, the locally
                        configured data (nameserver names and glue addresses)
                        is always used even if different authoritative
                        information is cached.
                      </p>
                      <p>
                        Zone data is configured via the
                        <span><strong class="command">server-addresses</strong></span> and
                        <span><strong class="command">server-names</strong></span> zone options.
                      </p>
                      <p>
                        The zone data is maintained in the form of NS
                        and (if necessary) glue A or AAAA RRs
                        internally, which can be seen by dumping zone
                        databases by <span><strong class="command">rndc dumpdb -all</strong></span>.
                        The configured RRs are considered local configuration
                        parameters rather than public data.
                        Non recursive queries (i.e., those with the RD
                        bit off) to a static-stub zone are therefore
                        prohibited and will be responded with REFUSED.
                      </p>
                      <p>
                        Since the data is statically configured, no
                        zone maintenance action takes place for a static-stub
                        zone.
                        For example, there is no periodic refresh
                        attempt, and an incoming notify message
                        will be rejected with an rcode of NOTAUTH.
                      </p>
                      <p>
                        Each static-stub zone is configured with
                        internally generated NS and (if necessary)
                        glue A or AAAA RRs 
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">forward</code>
                      </p>
                    </td>
<td>
                      <p>
                        A "forward zone" is a way to configure
                        forwarding on a per-domain basis.  A <span><strong class="command">zone</strong></span> statement
                        of type <span><strong class="command">forward</strong></span> can
                        contain a <span><strong class="command">forward</strong></span>
                        and/or <span><strong class="command">forwarders</strong></span>
                        statement,
                        which will apply to queries within the domain given by
                        the zone
                        name. If no <span><strong class="command">forwarders</strong></span>
                        statement is present or
                        an empty list for <span><strong class="command">forwarders</strong></span> is given, then no
                        forwarding will be done for the domain, canceling the
                        effects of
                        any forwarders in the <span><strong class="command">options</strong></span> statement. Thus
                        if you want to use this type of zone to change the
                        behavior of the
                        global <span><strong class="command">forward</strong></span> option
                        (that is, "forward first"
                        to, then "forward only", or vice versa, but want to
                        use the same
                        servers as set globally) you need to re-specify the
                        global forwarders.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">hint</code>
                      </p>
                    </td>
<td>
                      <p>
                        The initial set of root name servers is
                        specified using a "hint zone". When the server starts
                        up, it uses
                        the root hints to find a root name server and get the
                        most recent
                        list of root name servers. If no hint zone is
                        specified for class
                        IN, the server uses a compiled-in default set of root
                        servers hints.
                        Classes other than IN have no built-in defaults hints.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">redirect</code>
                      </p>
                    </td>
<td>
                      <p>
                        Redirect zones are used to provide answers to
                        queries when normal resolution would result in
                        NXDOMAIN being returned.
                        Only one redirect zone is supported
                        per view.  <span><strong class="command">allow-query</strong></span> can be
                        used to restrict which clients see these answers.
                      </p>
                      <p>
                        If the client has requested DNSSEC records (DO=1) and
                        the NXDOMAIN response is signed then no substitution
                        will occur.
                      </p>
                      <p>
                        To redirect all NXDOMAIN responses to
                        100.100.100.2 and
                        2001:ffff:ffff::100.100.100.2, one would
                        configure a type redirect zone named ".",
                        with the zone file containing wildcard records
                        that point to the desired addresses: 
                        <code class="literal">"*. IN A 100.100.100.2"</code>
                        and
                        <code class="literal">"*. IN AAAA 2001:ffff:ffff::100.100.100.2"</code>.
                      </p>
                      <p>
                        To redirect all Spanish names (under .ES) one
                        would use similar entries but with the names
                        "*.ES." instead of "*.".  To redirect all 
                        commercial Spanish names (under COM.ES) one
                        would use wildcard entries called "*.COM.ES.".
                      </p>
                      <p>
                        Note that the redirect zone supports all
                        possible types; it is not limited to A and
                        AAAA records.
                      </p>
                      <p>
                        Because redirect zones are not referenced
                        directly by name, they are not kept in the
                        zone lookup table with normal master and slave
                        zones. Consequently, it is not currently possible
                        to use
                        <span><strong class="command">rndc reload
                                <em class="replaceable"><code>zonename</code></em></strong></span>
                        to reload a redirect zone.  However, when using
                        <span><strong class="command">rndc reload</strong></span> without specifying
                        a zone name, redirect zones will be reloaded along
                        with other zones.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">delegation-only</code>
                      </p>
                    </td>
<td>
                      <p>
                        This is used to enforce the delegation-only
                        status of infrastructure zones (e.g. COM,
                        NET, ORG).  Any answer that is received
                        without an explicit or implicit delegation
                        in the authority section will be treated
                        as NXDOMAIN.  This does not apply to the
                        zone apex.  This should not be applied to
                        leaf zones.
                      </p>
                      <p>
                        <code class="varname">delegation-only</code> has no
                        effect on answers received from forwarders.
                      </p>
                      <p>
                        See caveats in <a href="Bv9ARM.ch06.html#root_delegation_only"><span><strong class="command">root-delegation-only</strong></span></a>.
                      </p>
                    </td>
</tr>
</tbody>
</table></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2593739"></a>Class</h4></div></div></div>
<p>
              The zone's name may optionally be followed by a class. If
              a class is not specified, class <code class="literal">IN</code> (for <code class="varname">Internet</code>),
              is assumed. This is correct for the vast majority of cases.
            </p>
<p>
              The <code class="literal">hesiod</code> class is
              named for an information service from MIT's Project Athena. It
              is
              used to share information about various systems databases, such
              as users, groups, printers and so on. The keyword
              <code class="literal">HS</code> is
              a synonym for hesiod.
            </p>
<p>
              Another MIT development is Chaosnet, a LAN protocol created
              in the mid-1970s. Zone data for it can be specified with the <code class="literal">CHAOS</code> class.
            </p>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2593772"></a>Zone Options</h4></div></div></div>
<div class="variablelist"><dl>
<dt><span class="term"><span><strong class="command">allow-notify</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">allow-notify</strong></span> in <a href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">allow-query</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">allow-query</strong></span> in <a href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">allow-query-on</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">allow-query-on</strong></span> in <a href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">allow-transfer</strong></span></span></dt>
<dd><p>
                    See the description of <span><strong class="command">allow-transfer</strong></span>
                    in <a href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">allow-update</strong></span></span></dt>
<dd><p>
                    See the description of <span><strong class="command">allow-update</strong></span>
                    in <a href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">update-policy</strong></span></span></dt>
<dd><p>
                    Specifies a "Simple Secure Update" policy. See
                    <a href="Bv9ARM.ch06.html#dynamic_update_policies" title="Dynamic Update Policies">the section called &#8220;Dynamic Update Policies&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">allow-update-forwarding</strong></span></span></dt>
<dd><p>
                    See the description of <span><strong class="command">allow-update-forwarding</strong></span>
                    in <a href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">also-notify</strong></span></span></dt>
<dd><p>
                    Only meaningful if <span><strong class="command">notify</strong></span>
                    is
                    active for this zone. The set of machines that will
                    receive a
                    <code class="literal">DNS NOTIFY</code> message
                    for this zone is made up of all the listed name servers
                    (other than
                    the primary master) for the zone plus any IP addresses
                    specified
                    with <span><strong class="command">also-notify</strong></span>. A port
                    may be specified
                    with each <span><strong class="command">also-notify</strong></span>
                    address to send the notify
                    messages to a port other than the default of 53.
                    A TSIG key may also be specified to cause the
                    <code class="literal">NOTIFY</code> to be signed by the
                    given key.
                    <span><strong class="command">also-notify</strong></span> is not
                    meaningful for stub zones.
                    The default is the empty list.
                  </p></dd>
<dt><span class="term"><span><strong class="command">check-names</strong></span></span></dt>
<dd><p>
                    This option is used to restrict the character set and
                    syntax of
                    certain domain names in master files and/or DNS responses
                    received from the
                    network.  The default varies according to zone type.  For <span><strong class="command">master</strong></span> zones the default is <span><strong class="command">fail</strong></span>.  For <span><strong class="command">slave</strong></span>
                    zones the default is <span><strong class="command">warn</strong></span>.
                    It is not implemented for <span><strong class="command">hint</strong></span> zones.
                  </p></dd>
<dt><span class="term"><span><strong class="command">check-mx</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">check-mx</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">check-spf</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">check-spf</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">check-wildcard</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">check-wildcard</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">check-integrity</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">check-integrity</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">check-sibling</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">check-sibling</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">zero-no-soa-ttl</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">zero-no-soa-ttl</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">update-check-ksk</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">update-check-ksk</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">dnssec-update-mode</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">dnssec-update-mode</strong></span> in <a href="Bv9ARM.ch06.html#options" title="options Statement Definition and
          Usage">the section called &#8220;<span><strong class="command">options</strong></span> Statement Definition and
          Usage&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">dnssec-dnskey-kskonly</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">dnssec-dnskey-kskonly</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">try-tcp-refresh</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">try-tcp-refresh</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">database</strong></span></span></dt>
<dd>
<p>
                    Specify the type of database to be used for storing the
                    zone data.  The string following the <span><strong class="command">database</strong></span> keyword
                    is interpreted as a list of whitespace-delimited words.
                    The first word
                    identifies the database type, and any subsequent words are
                    passed
                    as arguments to the database to be interpreted in a way
                    specific
                    to the database type.
                  </p>
<p>
                    The default is <strong class="userinput"><code>"rbt"</code></strong>, BIND 9's
                    native in-memory
                    red-black-tree database.  This database does not take
                    arguments.
                  </p>
<p>
                    Other values are possible if additional database drivers
                    have been linked into the server.  Some sample drivers are
                    included
                    with the distribution but none are linked in by default.
                  </p>
</dd>
<dt><span class="term"><span><strong class="command">dialup</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">dialup</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">delegation-only</strong></span></span></dt>
<dd>
<p>
                    The flag only applies to forward, hint and stub
                    zones.  If set to <strong class="userinput"><code>yes</code></strong>,
                    then the zone will also be treated as if it is
                    also a delegation-only type zone.
                  </p>
<p>
                    See caveats in <a href="Bv9ARM.ch06.html#root_delegation_only"><span><strong class="command">root-delegation-only</strong></span></a>.
                  </p>
</dd>
<dt><span class="term"><span><strong class="command">forward</strong></span></span></dt>
<dd><p>
                    Only meaningful if the zone has a forwarders
                    list. The <span><strong class="command">only</strong></span> value causes
                    the lookup to fail
                    after trying the forwarders and getting no answer, while <span><strong class="command">first</strong></span> would
                    allow a normal lookup to be tried.
                  </p></dd>
<dt><span class="term"><span><strong class="command">forwarders</strong></span></span></dt>
<dd><p>
                    Used to override the list of global forwarders.
                    If it is not specified in a zone of type <span><strong class="command">forward</strong></span>,
                    no forwarding is done for the zone and the global options are
                    not used.
                  </p></dd>
<dt><span class="term"><span><strong class="command">ixfr-base</strong></span></span></dt>
<dd><p>
                    Was used in <acronym class="acronym">BIND</acronym> 8 to
                    specify the name
                    of the transaction log (journal) file for dynamic update
                    and IXFR.
                    <acronym class="acronym">BIND</acronym> 9 ignores the option
                    and constructs the name of the journal
                    file by appending "<code class="filename">.jnl</code>"
                    to the name of the
                    zone file.
                  </p></dd>
<dt><span class="term"><span><strong class="command">ixfr-tmp-file</strong></span></span></dt>
<dd><p>
                    Was an undocumented option in <acronym class="acronym">BIND</acronym> 8.
                    Ignored in <acronym class="acronym">BIND</acronym> 9.
                  </p></dd>
<dt><span class="term"><span><strong class="command">journal</strong></span></span></dt>
<dd><p>
                    Allow the default journal's filename to be overridden.
                    The default is the zone's filename with "<code class="filename">.jnl</code>" appended.
                    This is applicable to <span><strong class="command">master</strong></span> and <span><strong class="command">slave</strong></span> zones.
                  </p></dd>
<dt><span class="term"><span><strong class="command">max-journal-size</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">max-journal-size</strong></span> in <a href="Bv9ARM.ch06.html#server_resource_limits" title="Server  Resource Limits">the section called &#8220;Server  Resource Limits&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">max-transfer-time-in</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">max-transfer-time-in</strong></span> in <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">max-transfer-idle-in</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">max-transfer-idle-in</strong></span> in <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">max-transfer-time-out</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">max-transfer-time-out</strong></span> in <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">max-transfer-idle-out</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">max-transfer-idle-out</strong></span> in <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">notify</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">notify</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">notify-delay</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">notify-delay</strong></span> in <a href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">notify-to-soa</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">notify-to-soa</strong></span> in
                    <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">pubkey</strong></span></span></dt>
<dd><p>
                    In <acronym class="acronym">BIND</acronym> 8, this option was
                    intended for specifying
                    a public zone key for verification of signatures in DNSSEC
                    signed
                    zones when they are loaded from disk. <acronym class="acronym">BIND</acronym> 9 does not verify signatures
                    on load and ignores the option.
                  </p></dd>
<dt><span class="term"><span><strong class="command">zone-statistics</strong></span></span></dt>
<dd><p>
                    If <strong class="userinput"><code>yes</code></strong>, the server will keep
                    statistical
                    information for this zone, which can be dumped to the
                    <span><strong class="command">statistics-file</strong></span> defined in
                    the server options.
                  </p></dd>
<dt><span class="term"><span><strong class="command">server-addresses</strong></span></span></dt>
<dd>
<p>
                    Only meaningful for static-stub zones.
                    This is a list of IP addresses to which queries
                    should be sent in recursive resolution for the
                    zone.
                    A non empty list for this option will internally
                    configure the apex NS RR with associated glue A or
                    AAAA RRs.
                  </p>
<p>
                    For example, if "example.com" is configured as a
                    static-stub zone with 192.0.2.1 and 2001:db8::1234
                    in a <span><strong class="command">server-addresses</strong></span> option,
                    the following RRs will be internally configured.
                  </p>
<pre class="programlisting">example.com. NS example.com.
example.com. A 192.0.2.1
example.com. AAAA 2001:db8::1234</pre>
<p>
                    These records are internally used to resolve
                    names under the static-stub zone.
                    For instance, if the server receives a query for
                    "www.example.com" with the RD bit on, the server
                    will initiate recursive resolution and send
                    queries to 192.0.2.1 and/or 2001:db8::1234.
                  </p>
</dd>
<dt><span class="term"><span><strong class="command">server-names</strong></span></span></dt>
<dd>
<p>
                    Only meaningful for static-stub zones.
                    This is a list of domain names of nameservers that
                    act as authoritative servers of the static-stub
                    zone.
                    These names will be resolved to IP addresses when
                    <span><strong class="command">named</strong></span> needs to send queries to
                    these servers.
                    To make this supplemental resolution successful,
                    these names must not be a subdomain of the origin
                    name of static-stub zone.
                    That is, when "example.net" is the origin of a
                    static-stub zone, "ns.example" and
                    "master.example.com" can be specified in the
                    <span><strong class="command">server-names</strong></span> option, but
                    "ns.example.net" cannot, and will be rejected by
                    the configuration parser.
                  </p>
<p>
                    A non empty list for this option will internally
                    configure the apex NS RR with the specified names.
                    For example, if "example.com" is configured as a
                    static-stub zone with "ns1.example.net" and
                    "ns2.example.net"
                    in a <span><strong class="command">server-names</strong></span> option,
                    the following RRs will be internally configured.
                  </p>
<pre class="programlisting">example.com. NS ns1.example.net.
example.com. NS ns2.example.net.
</pre>
<p>
                    These records are internally used to resolve
                    names under the static-stub zone.
                    For instance, if the server receives a query for
                    "www.example.com" with the RD bit on, the server
                    initiate recursive resolution,
                    resolve "ns1.example.net" and/or
                    "ns2.example.net" to IP addresses, and then send
                    queries to (one or more of) these addresses.
                  </p>
</dd>
<dt><span class="term"><span><strong class="command">sig-validity-interval</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">sig-validity-interval</strong></span> in <a href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">sig-signing-nodes</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">sig-signing-nodes</strong></span> in <a href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">sig-signing-signatures</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">sig-signing-signatures</strong></span> in <a href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">sig-signing-type</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">sig-signing-type</strong></span> in <a href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">transfer-source</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">transfer-source</strong></span> in <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">transfer-source-v6</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">transfer-source-v6</strong></span> in <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">alt-transfer-source</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">alt-transfer-source</strong></span> in <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">alt-transfer-source-v6</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">alt-transfer-source-v6</strong></span> in <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">use-alt-transfer-source</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">use-alt-transfer-source</strong></span> in <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">notify-source</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">notify-source</strong></span> in <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">notify-source-v6</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">notify-source-v6</strong></span> in <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
                  </p></dd>
<dt>
<span class="term"><span><strong class="command">min-refresh-time</strong></span>, </span><span class="term"><span><strong class="command">max-refresh-time</strong></span>, </span><span class="term"><span><strong class="command">min-retry-time</strong></span>, </span><span class="term"><span><strong class="command">max-retry-time</strong></span></span>
</dt>
<dd><p>
                    See the description in <a href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">ixfr-from-differences</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">ixfr-from-differences</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                    (Note that the <span><strong class="command">ixfr-from-differences</strong></span>
                    <strong class="userinput"><code>master</code></strong> and
                    <strong class="userinput"><code>slave</code></strong> choices are not
                    available at the zone level.)
                  </p></dd>
<dt><span class="term"><span><strong class="command">key-directory</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">key-directory</strong></span> in <a href="Bv9ARM.ch06.html#options" title="options Statement Definition and
          Usage">the section called &#8220;<span><strong class="command">options</strong></span> Statement Definition and
          Usage&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">auto-dnssec</strong></span></span></dt>
<dd>
<p>
                    Zones configured for dynamic DNS may also use this
                    option to allow varying levels of automatic DNSSEC key
                    management. There are three possible settings:
                  </p>
<p>
                    <span><strong class="command">auto-dnssec allow;</strong></span> permits
                    keys to be updated and the zone fully re-signed
                    whenever the user issues the command <span><strong class="command">rndc sign
                    <em class="replaceable"><code>zonename</code></em></strong></span>.
                  </p>
<p>
                    <span><strong class="command">auto-dnssec maintain;</strong></span> includes the
                    above, but also automatically adjusts the zone's DNSSEC
                    keys on schedule, according to the keys' timing metadata
                    (see <a href="man.dnssec-keygen.html" title="dnssec-keygen"><span class="refentrytitle"><span class="application">dnssec-keygen</span></span>(8)</a> and
                    <a href="man.dnssec-settime.html" title="dnssec-settime"><span class="refentrytitle"><span class="application">dnssec-settime</span></span>(8)</a>).  The command
                    <span><strong class="command">rndc sign
                    <em class="replaceable"><code>zonename</code></em></strong></span> causes
                    <span><strong class="command">named</strong></span> to load keys from the key
                    repository and sign the zone with all keys that are
                    active. 
                    <span><strong class="command">rndc loadkeys
                    <em class="replaceable"><code>zonename</code></em></strong></span> causes
                    <span><strong class="command">named</strong></span> to load keys from the key
                    repository and schedule key maintenance events to occur
                    in the future, but it does not sign the full zone
                    immediately.  Note: once keys have been loaded for a
                    zone the first time, the repository will be searched
                    for changes periodically, regardless of whether
                    <span><strong class="command">rndc loadkeys</strong></span> is used.  The recheck
                    interval is defined by
                    <span><strong class="command">dnssec-loadkeys-interval</strong></span>.)
                  </p>
<p>
                    The default setting is <span><strong class="command">auto-dnssec off</strong></span>.
                  </p>
</dd>
<dt><span class="term"><span><strong class="command">serial-update-method</strong></span></span></dt>
<dd>
<p>
                    Zones configured for dynamic DNS may use this
                    option to set the update method that will be used for
                    the zone serial number in the SOA record.
                  </p>
<p>
                    With the default setting of
                    <span><strong class="command">serial-update-method increment;</strong></span>, the
                    SOA serial number will be incremented by one each time
                    the zone is updated.
                  </p>
<p>
                    When set to 
                    <span><strong class="command">serial-update-method unixtime;</strong></span>, the
                    SOA serial number will be set to the number of seconds
                    since the UNIX epoch, unless the serial number is
                    already greater than or equal to that value, in which
                    case it is simply incremented by one.
                  </p>
</dd>
<dt><span class="term"><span><strong class="command">inline-signing</strong></span></span></dt>
<dd><p>
                    If <code class="literal">yes</code>, this enables
                    "bump in the wire" signing of a zone, where a
                    unsigned zone is transferred in or loaded from
                    disk and a signed version of the zone is served,
                    with possibly, a different serial number.  This
                    behaviour is disabled by default.
                  </p></dd>
<dt><span class="term"><span><strong class="command">multi-master</strong></span></span></dt>
<dd><p>
                    See the description of <span><strong class="command">multi-master</strong></span> in
                    <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">masterfile-format</strong></span></span></dt>
<dd><p>
                    See the description of <span><strong class="command">masterfile-format</strong></span>
                    in <a href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
                  </p></dd>
<dt><span class="term"><span><strong class="command">dnssec-secure-to-insecure</strong></span></span></dt>
<dd><p>
                    See the description of
                    <span><strong class="command">dnssec-secure-to-insecure</strong></span> in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
                  </p></dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="dynamic_update_policies"></a>Dynamic Update Policies</h4></div></div></div>
<p><acronym class="acronym">BIND</acronym> 9 supports two alternative
              methods of granting clients the right to perform
              dynamic updates to a zone, configured by the
              <span><strong class="command">allow-update</strong></span> and
              <span><strong class="command">update-policy</strong></span> option, respectively.
            </p>
<p>
              The <span><strong class="command">allow-update</strong></span> clause works the
              same way as in previous versions of <acronym class="acronym">BIND</acronym>.
              It grants given clients the permission to update any
              record of any name in the zone.
            </p>
<p>
              The <span><strong class="command">update-policy</strong></span> clause
              allows more fine-grained control over what updates are
              allowed.  A set of rules is specified, where each rule
              either grants or denies permissions for one or more
              names to be updated by one or more identities.  If
              the dynamic update request message is signed (that is,
              it includes either a TSIG or SIG(0) record), the
              identity of the signer can be determined.
            </p>
<p>
              Rules are specified in the <span><strong class="command">update-policy</strong></span>
              zone option, and are only meaningful for master zones.
              When the <span><strong class="command">update-policy</strong></span> statement
              is present, it is a configuration error for the
              <span><strong class="command">allow-update</strong></span> statement to be
              present.  The <span><strong class="command">update-policy</strong></span> statement
              only examines the signer of a message; the source
              address is not relevant.
            </p>
<p>
              There is a pre-defined <span><strong class="command">update-policy</strong></span>
              rule which can be switched on with the command
              <span><strong class="command">update-policy local;</strong></span>.
              Switching on this rule in a zone causes
              <span><strong class="command">named</strong></span> to generate a TSIG session
              key and place it in a file, and to allow that key
              to update the zone.  (By default, the file is
              <code class="filename">/var/run/named/session.key</code>, the key
              name is "local-ddns" and the key algorithm is HMAC-SHA256,
              but these values are configurable with the
              <span><strong class="command">session-keyfile</strong></span>,
              <span><strong class="command">session-keyname</strong></span> and
              <span><strong class="command">session-keyalg</strong></span> options, respectively).
            </p>
<p>
              A client running on the local system, and with appropriate
              permissions, may read that file and use the key to sign update
              requests.  The zone's update policy will be set to allow that
              key to change any record within the zone.  Assuming the
              key name is "local-ddns", this policy is equivalent to:
            </p>
<pre class="programlisting">update-policy { grant local-ddns zonesub any; };
            </pre>
<p>
              The command <span><strong class="command">nsupdate -l</strong></span> sends update
              requests to localhost, and signs them using the session key.
            </p>
<p>
              Other rule definitions look like this:
            </p>
<pre class="programlisting">
( <span><strong class="command">grant</strong></span> | <span><strong class="command">deny</strong></span> ) <em class="replaceable"><code>identity</code></em> <em class="replaceable"><code>nametype</code></em> [<span class="optional"> <em class="replaceable"><code>name</code></em> </span>] [<span class="optional"> <em class="replaceable"><code>types</code></em> </span>]
</pre>
<p>
              Each rule grants or denies privileges.  Once a message has
              successfully matched a rule, the operation is immediately
              granted or denied and no further rules are examined.  A rule
              is matched when the signer matches the identity field, the
              name matches the name field in accordance with the nametype
              field, and the type matches the types specified in the type
              field.
            </p>
<p>
              No signer is required for <em class="replaceable"><code>tcp-self</code></em>
              or <em class="replaceable"><code>6to4-self</code></em> however the standard
              reverse mapping / prefix conversion must match the identity
              field.
            </p>
<p>
              The identity field specifies a name or a wildcard
              name.  Normally, this is the name of the TSIG or
              SIG(0) key used to sign the update request.  When a
              TKEY exchange has been used to create a shared secret,
              the identity of the shared secret is the same as the
              identity of the key used to authenticate the TKEY
              exchange.  TKEY is also the negotiation method used
              by GSS-TSIG, which establishes an identity that is
              the Kerberos principal of the client, such as
              <strong class="userinput"><code>"user@host.domain"</code></strong>.  When the
              <em class="replaceable"><code>identity</code></em> field specifies
              a wildcard name, it is subject to DNS wildcard
              expansion, so the rule will apply to multiple identities.
              The <em class="replaceable"><code>identity</code></em> field must
              contain a fully-qualified domain name.
            </p>
<p>
              For nametypes <code class="varname">krb5-self</code>,
              <code class="varname">ms-self</code>, <code class="varname">krb5-subdomain</code>,
              and <code class="varname">ms-subdomain</code> the
              <em class="replaceable"><code>identity</code></em> field specifies
              the Windows or Kerberos realm of the machine belongs to.
            </p>
<p>
              The <em class="replaceable"><code>nametype</code></em> field has 13
              values:
              <code class="varname">name</code>, <code class="varname">subdomain</code>,
              <code class="varname">wildcard</code>, <code class="varname">self</code>,
              <code class="varname">selfsub</code>, <code class="varname">selfwild</code>,
              <code class="varname">krb5-self</code>, <code class="varname">ms-self</code>,
              <code class="varname">krb5-subdomain</code>,
              <code class="varname">ms-subdomain</code>,
              <code class="varname">tcp-self</code>, <code class="varname">6to4-self</code>,
              <code class="varname">zonesub</code>, and <code class="varname">external</code>.
            </p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                      <p>
                        <code class="varname">name</code>
                      </p>
                    </td>
<td>
                      <p>
                        Exact-match semantics.  This rule matches
                        when the name being updated is identical
                        to the contents of the
                        <em class="replaceable"><code>name</code></em> field.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">subdomain</code>
                      </p>
                    </td>
<td>
                      <p>
                        This rule matches when the name being updated
                        is a subdomain of, or identical to, the
                        contents of the <em class="replaceable"><code>name</code></em>
                        field.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">zonesub</code>
                      </p>
                    </td>
<td>
                      <p>
                        This rule is similar to subdomain, except that
                        it matches when the name being updated is a
                        subdomain of the zone in which the
                        <span><strong class="command">update-policy</strong></span> statement
                        appears.  This obviates the need to type the zone
                        name twice, and enables the use of a standard
                        <span><strong class="command">update-policy</strong></span> statement in
                        multiple zones without modification.
                      </p>
                      <p>
                        When this rule is used, the
                        <em class="replaceable"><code>name</code></em> field is omitted.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">wildcard</code>
                      </p>
                    </td>
<td>
                      <p>
                        The <em class="replaceable"><code>name</code></em> field
                        is subject to DNS wildcard expansion, and
                        this rule matches when the name being updated
                        name is a valid expansion of the wildcard.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">self</code>
                      </p>
                    </td>
<td>
                      <p>
                        This rule matches when the name being updated
                        matches the contents of the
                        <em class="replaceable"><code>identity</code></em> field.
                        The <em class="replaceable"><code>name</code></em> field
                        is ignored, but should be the same as the
                        <em class="replaceable"><code>identity</code></em> field.
                        The <code class="varname">self</code> nametype is
                        most useful when allowing using one key per
                        name to update, where the key has the same
                        name as the name to be updated.  The
                        <em class="replaceable"><code>identity</code></em> would
                        be specified as <code class="constant">*</code> (an asterisk) in
                        this case.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">selfsub</code>
                      </p>
                    </td>
<td>
                      <p>
                        This rule is similar to <code class="varname">self</code>
                        except that subdomains of <code class="varname">self</code>
                        can also be updated.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">selfwild</code>
                      </p>
                    </td>
<td>
                      <p>
                        This rule is similar to <code class="varname">self</code>
                        except that only subdomains of
                        <code class="varname">self</code> can be updated.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">ms-self</code>
                      </p>
                    </td>
<td>
                      <p>
                        This rule takes a Windows machine principal
                        (machine$@REALM) for machine in REALM and
                        and converts it machine.realm allowing the machine 
                        to update machine.realm.  The REALM to be matched
                        is specified in the <em class="replaceable"><code>identity</code></em>
                        field.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">ms-subdomain</code>
                      </p>
                    </td>
<td>
                      <p>
                        This rule takes a Windows machine principal 
                        (machine$@REALM) for machine in REALM and
                        converts it to machine.realm allowing the machine
                        to update subdomains of machine.realm.  The REALM
                        to be matched is specified in the
                        <em class="replaceable"><code>identity</code></em> field.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">krb5-self</code>
                      </p>
                    </td>
<td>
                      <p>
                        This rule takes a Kerberos machine principal
                        (host/machine@REALM) for machine in REALM and
                        and converts it machine.realm allowing the machine 
                        to update machine.realm.  The REALM to be matched
                        is specified in the <em class="replaceable"><code>identity</code></em>
                        field.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">krb5-subdomain</code>
                      </p>
                    </td>
<td>
                      <p>
                        This rule takes a Kerberos machine principal 
                        (host/machine@REALM) for machine in REALM and
                        converts it to machine.realm allowing the machine
                        to update subdomains of machine.realm.  The REALM
                        to be matched is specified in the
                        <em class="replaceable"><code>identity</code></em> field.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">tcp-self</code>
                      </p>
                    </td>
<td>
                      <p>
                        Allow updates that have been sent via TCP and
                        for which the standard mapping from the initiating
                        IP address into the IN-ADDR.ARPA and IP6.ARPA
                        namespaces match the name to be updated.
                      </p>
                      <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
                        It is theoretically possible to spoof these TCP
                        sessions.
                      </div>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">6to4-self</code>
                      </p>
                    </td>
<td>
                      <p>
                        Allow the 6to4 prefix to be update by any TCP
                        connection from the 6to4 network or from the
                        corresponding IPv4 address.  This is intended
                        to allow NS or DNAME RRsets to be added to the
                        reverse tree.
                      </p>
                      <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
                        It is theoretically possible to spoof these TCP
                        sessions.
                      </div>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        <code class="varname">external</code>
                      </p>
                    </td>
<td>
                      <p>
                        This rule allows <span><strong class="command">named</strong></span>
                        to defer the decision of whether to allow a
                        given update to an external daemon.
                      </p>
                      <p>
                        The method of communicating with the daemon is
                        specified in the <em class="replaceable"><code>identity</code></em>
                        field, the format of which is
                        "<code class="constant">local:</code><em class="replaceable"><code>path</code></em>",
                        where <em class="replaceable"><code>path</code></em> is the location
                        of a UNIX-domain socket.  (Currently, "local" is the
                        only supported mechanism.)
                      </p>
                      <p>
                        Requests to the external daemon are sent over the
                        UNIX-domain socket as datagrams with the following
                        format:
                      </p>
                      <pre class="programlisting">
   Protocol version number (4 bytes, network byte order, currently 1)
   Request length (4 bytes, network byte order)
   Signer (null-terminated string)
   Name (null-terminated string)
   TCP source address (null-terminated string)
   Rdata type (null-terminated string)
   Key (null-terminated string)
   TKEY token length (4 bytes, network byte order)
   TKEY token (remainder of packet)</pre>
                      <p>
                        The daemon replies with a four-byte value in
                        network byte order, containing either 0 or 1; 0
                        indicates that the specified update is not
                        permitted, and 1 indicates that it is.
                      </p>
                    </td>
</tr>
</tbody>
</table></div>
<p>
              In all cases, the <em class="replaceable"><code>name</code></em>
              field must specify a fully-qualified domain name.
            </p>
<p>
              If no types are explicitly specified, this rule matches
              all types except RRSIG, NS, SOA, NSEC and NSEC3. Types
              may be specified by name, including "ANY" (ANY matches
              all types except NSEC and NSEC3, which can never be
              updated).  Note that when an attempt is made to delete
              all records associated with a name, the rules are
              checked for each existing record type.
            </p>
</div>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2596605"></a>Zone File</h2></div></div></div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="types_of_resource_records_and_when_to_use_them"></a>Types of Resource Records and When to Use Them</h3></div></div></div>
<p>
            This section, largely borrowed from RFC 1034, describes the
            concept of a Resource Record (RR) and explains when each is used.
            Since the publication of RFC 1034, several new RRs have been
            identified
            and implemented in the DNS. These are also included.
          </p>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2596624"></a>Resource Records</h4></div></div></div>
<p>
              A domain name identifies a node.  Each node has a set of
              resource information, which may be empty.  The set of resource
              information associated with a particular name is composed of
              separate RRs. The order of RRs in a set is not significant and
              need not be preserved by name servers, resolvers, or other
              parts of the DNS. However, sorting of multiple RRs is
              permitted for optimization purposes, for example, to specify
              that a particular nearby server be tried first. See <a href="Bv9ARM.ch06.html#the_sortlist_statement" title="The sortlist Statement">the section called &#8220;The <span><strong class="command">sortlist</strong></span> Statement&#8221;</a> and <a href="Bv9ARM.ch06.html#rrset_ordering" title="RRset Ordering">the section called &#8220;RRset Ordering&#8221;</a>.
            </p>
<p>
              The components of a Resource Record are:
            </p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                      <p>
                        owner name
                      </p>
                    </td>
<td>
                      <p>
                        The domain name where the RR is found.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        type
                      </p>
                    </td>
<td>
                      <p>
                        An encoded 16-bit value that specifies
                        the type of the resource record.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        TTL
                      </p>
                    </td>
<td>
                      <p>
                        The time-to-live of the RR. This field
                        is a 32-bit integer in units of seconds, and is
                        primarily used by
                        resolvers when they cache RRs. The TTL describes how
                        long a RR can
                        be cached before it should be discarded.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        class
                      </p>
                    </td>
<td>
                      <p>
                        An encoded 16-bit value that identifies
                        a protocol family or instance of a protocol.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        RDATA
                      </p>
                    </td>
<td>
                      <p>
                        The resource data.  The format of the
                        data is type (and sometimes class) specific.
                      </p>
                    </td>
</tr>
</tbody>
</table></div>
<p>
              The following are <span class="emphasis"><em>types</em></span> of valid RRs:
            </p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                      <p>
                        A
                      </p>
                    </td>
<td>
                      <p>
                        A host address.  In the IN class, this is a
                        32-bit IP address.  Described in RFC 1035.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        AAAA
                      </p>
                    </td>
<td>
                      <p>
                        IPv6 address.  Described in RFC 1886.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        A6
                      </p>
                    </td>
<td>
                      <p>
                        IPv6 address.  This can be a partial
                        address (a suffix) and an indirection to the name
                        where the rest of the
                        address (the prefix) can be found.  Experimental.
                        Described in RFC 2874.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        AFSDB
                      </p>
                    </td>
<td>
                      <p>
                        Location of AFS database servers.
                        Experimental.  Described in RFC 1183.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        APL
                      </p>
                    </td>
<td>
                      <p>
                        Address prefix list.  Experimental.
                        Described in RFC 3123.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        CERT
                      </p>
                    </td>
<td>
                      <p>
                        Holds a digital certificate.
                        Described in RFC 2538.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        CNAME
                      </p>
                    </td>
<td>
                      <p>
                        Identifies the canonical name of an alias.
                        Described in RFC 1035.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        DHCID
                      </p>
                    </td>
<td>
                      <p>
                        Is used for identifying which DHCP client is
                        associated with this name.  Described in RFC 4701.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        DNAME
                      </p>
                    </td>
<td>
                      <p>
                        Replaces the domain name specified with
                        another name to be looked up, effectively aliasing an
                        entire
                        subtree of the domain name space rather than a single
                        record
                        as in the case of the CNAME RR.
                        Described in RFC 2672.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        DNSKEY
                      </p>
                    </td>
<td>
                      <p>
                        Stores a public key associated with a signed
                        DNS zone.  Described in RFC 4034.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        DS
                      </p>
                    </td>
<td>
                      <p>
                        Stores the hash of a public key associated with a
                        signed DNS zone.  Described in RFC 4034.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        GPOS
                      </p>
                    </td>
<td>
                      <p>
                        Specifies the global position.  Superseded by LOC.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        HINFO
                      </p>
                    </td>
<td>
                      <p>
                        Identifies the CPU and OS used by a host.
                        Described in RFC 1035.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        IPSECKEY
                      </p>
                    </td>
<td>
                      <p>
                        Provides a method for storing IPsec keying material in
                        DNS.  Described in RFC 4025.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        ISDN
                      </p>
                    </td>
<td>
                      <p>
                        Representation of ISDN addresses.
                        Experimental.  Described in RFC 1183.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        KEY
                      </p>
                    </td>
<td>
                      <p>
                        Stores a public key associated with a
                        DNS name.  Used in original DNSSEC; replaced
                        by DNSKEY in DNSSECbis, but still used with
                        SIG(0).  Described in RFCs 2535 and 2931.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        KX
                      </p>
                    </td>
<td>
                      <p>
                        Identifies a key exchanger for this
                        DNS name.  Described in RFC 2230.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        LOC
                      </p>
                    </td>
<td>
                      <p>
                        For storing GPS info.  Described in RFC 1876.
                        Experimental.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        MX
                      </p>
                    </td>
<td>
                      <p>
                        Identifies a mail exchange for the domain with
                        a 16-bit preference value (lower is better)
                        followed by the host name of the mail exchange.
                        Described in RFC 974, RFC 1035.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        NAPTR
                      </p>
                    </td>
<td>
                      <p>
                        Name authority pointer.  Described in RFC 2915.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        NSAP
                      </p>
                    </td>
<td>
                      <p>
                        A network service access point.
                        Described in RFC 1706.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        NS
                      </p>
                    </td>
<td>
                      <p>
                        The authoritative name server for the
                        domain.  Described in RFC 1035.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        NSEC
                      </p>
                    </td>
<td>
                      <p>
                        Used in DNSSECbis to securely indicate that
                        RRs with an owner name in a certain name interval do
                        not exist in
                        a zone and indicate what RR types are present for an
                        existing name.
                        Described in RFC 4034.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        NSEC3
                      </p>
                    </td>
<td>
                      <p>
                        Used in DNSSECbis to securely indicate that
                        RRs with an owner name in a certain name
                        interval do not exist in a zone and indicate
                        what RR types are present for an existing
                        name.  NSEC3 differs from NSEC in that it
                        prevents zone enumeration but is more
                        computationally expensive on both the server
                        and the client than NSEC.  Described in RFC
                        5155.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        NSEC3PARAM
                      </p>
                    </td>
<td>
                      <p>
                        Used in DNSSECbis to tell the authoritative
                        server which NSEC3 chains are available to use.
                        Described in RFC 5155.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        NXT
                      </p>
                    </td>
<td>
                      <p>
                        Used in DNSSEC to securely indicate that
                        RRs with an owner name in a certain name interval do
                        not exist in
                        a zone and indicate what RR types are present for an
                        existing name.
                        Used in original DNSSEC; replaced by NSEC in
                        DNSSECbis.
                        Described in RFC 2535.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        PTR
                      </p>
                    </td>
<td>
                      <p>
                        A pointer to another part of the domain
                        name space.  Described in RFC 1035.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        PX
                      </p>
                    </td>
<td>
                      <p>
                        Provides mappings between RFC 822 and X.400
                        addresses.  Described in RFC 2163.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        RP
                      </p>
                    </td>
<td>
                      <p>
                        Information on persons responsible
                        for the domain.  Experimental.  Described in RFC 1183.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        RRSIG
                      </p>
                    </td>
<td>
                      <p>
                        Contains DNSSECbis signature data.  Described
                        in RFC 4034.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        RT
                      </p>
                    </td>
<td>
                      <p>
                        Route-through binding for hosts that
                        do not have their own direct wide area network
                        addresses.
                        Experimental.  Described in RFC 1183.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        SIG
                      </p>
                    </td>
<td>
                      <p>
                        Contains DNSSEC signature data.  Used in
                        original DNSSEC; replaced by RRSIG in
                        DNSSECbis, but still used for SIG(0).
                        Described in RFCs 2535 and 2931.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        SOA
                      </p>
                    </td>
<td>
                      <p>
                        Identifies the start of a zone of authority.
                        Described in RFC 1035.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        SPF
                      </p>
                    </td>
<td>
                      <p>
                        Contains the Sender Policy Framework information
                        for a given email domain.  Described in RFC 4408.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        SRV
                      </p>
                    </td>
<td>
                      <p>
                        Information about well known network
                        services (replaces WKS).  Described in RFC 2782.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        SSHFP
                      </p>
                    </td>
<td>
                      <p>
                        Provides a way to securely publish a secure shell key's
                        fingerprint.  Described in RFC 4255.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        TXT
                      </p>
                    </td>
<td>
                      <p>
                        Text records.  Described in RFC 1035.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        WKS
                      </p>
                    </td>
<td>
                      <p>
                        Information about which well known
                        network services, such as SMTP, that a domain
                        supports. Historical.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        X25
                      </p>
                    </td>
<td>
                      <p>
                        Representation of X.25 network addresses.
                        Experimental.  Described in RFC 1183.
                      </p>
                    </td>
</tr>
</tbody>
</table></div>
<p>
              The following <span class="emphasis"><em>classes</em></span> of resource records
              are currently valid in the DNS:
            </p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>
                      <p>
                        IN
                      </p>
                    </td>
<td>
                      <p>
                        The Internet.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        CH
                      </p>
                    </td>
<td>
                      <p>
                        Chaosnet, a LAN protocol created at MIT in the
                        mid-1970s.
                        Rarely used for its historical purpose, but reused for
                        BIND's
                        built-in server information zones, e.g.,
                        <code class="literal">version.bind</code>.
                      </p>
                    </td>
</tr>
<tr>
<td>
                      <p>
                        HS
                      </p>
                    </td>
<td>
                      <p>
                        Hesiod, an information service
                        developed by MIT's Project Athena. It is used to share
                        information
                        about various systems databases, such as users,
                        groups, printers
                        and so on.
                      </p>
                    </td>
</tr>
</tbody>
</table></div>
<p>
              The owner name is often implicit, rather than forming an
              integral
              part of the RR.  For example, many name servers internally form
              tree
              or hash structures for the name space, and chain RRs off nodes.
              The remaining RR parts are the fixed header (type, class, TTL)
              which is consistent for all RRs, and a variable part (RDATA)
              that
              fits the needs of the resource being described.
            </p>
<p>
              The meaning of the TTL field is a time limit on how long an
              RR can be kept in a cache.  This limit does not apply to
              authoritative
              data in zones; it is also timed out, but by the refreshing
              policies
              for the zone.  The TTL is assigned by the administrator for the
              zone where the data originates.  While short TTLs can be used to
              minimize caching, and a zero TTL prohibits caching, the
              realities
              of Internet performance suggest that these times should be on
              the
              order of days for the typical host.  If a change can be
              anticipated,
              the TTL can be reduced prior to the change to minimize
              inconsistency
              during the change, and then increased back to its former value
              following
              the change.
            </p>
<p>
              The data in the RDATA section of RRs is carried as a combination
              of binary strings and domain names.  The domain names are
              frequently
              used as "pointers" to other data in the DNS.
            </p>