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<div class="chapter">
<div class="titlepage"><div><div><h1 class="title">
<a name="Bv9ARM.ch06"></a>Chapter 6. <acronym class="acronym">BIND</acronym> 9 Configuration Reference</h1></div></div></div>
<div class="toc">
Table of Contents
<dl class="toc">
<dt><a href="Bv9ARM.ch06.html#configuration_file_elements">Configuration File Elements</a></dt>
<dd><dl>
<dt><a href="Bv9ARM.ch06.html#address_match_lists">Address Match Lists</a></dt>
<dt><a href="Bv9ARM.ch06.html#comment_syntax">Comment Syntax</a></dt>
</dl></dd>
<dt><a href="Bv9ARM.ch06.html#Configuration_File_Grammar">Configuration File Grammar</a></dt>
<dd><dl>
<dt><a href="Bv9ARM.ch06.html#acl_grammar">acl Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#acl">acl Statement Definition and
 Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#controls_grammar">controls Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#controls_statement_definition_and_usage">controls Statement Definition and
 Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#include_grammar">include Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#include_statement">include Statement Definition and Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#key_grammar">key Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#key_statement">key Statement Definition and Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#logging_grammar">logging Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#logging_statement">logging Statement Definition and Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#lwres_grammar">lwres Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#lwres_statement">lwres Statement Definition and Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#masters_grammar">masters Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#masters_statement">masters Statement Definition and
 Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#options_grammar">options Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#options">options Statement Definition and
 Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#server_statement_grammar">server Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#server_statement_definition_and_usage">server Statement Definition and
 Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#statschannels">statistics-channels Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#statistics_channels">statistics-channels Statement Definition and
 Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#trusted-keys">trusted-keys Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#trusted_keys">trusted-keys Statement Definition
 and Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#managed_keys">managed-keys Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#managed-keys">managed-keys Statement Definition
 and Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#view_statement_grammar">view Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#view_statement">view Statement Definition and Usage</a></dt>
<dt><a href="Bv9ARM.ch06.html#zone_statement_grammar">zone
 Statement Grammar</a></dt>
<dt><a href="Bv9ARM.ch06.html#zone_statement">zone Statement Definition and Usage</a></dt>
</dl></dd>
<dt><a href="Bv9ARM.ch06.html#zone_file">Zone File</a></dt>
<dd><dl>
<dt><a href="Bv9ARM.ch06.html#types_of_resource_records_and_when_to_use_them">Types of Resource Records and When to Use Them</a></dt>
<dt><a href="Bv9ARM.ch06.html#mx_records">Discussion of MX Records</a></dt>
<dt><a href="Bv9ARM.ch06.html#Setting_TTLs">Setting TTLs</a></dt>
<dt><a href="Bv9ARM.ch06.html#ipv4_reverse">Inverse Mapping in IPv4</a></dt>
<dt><a href="Bv9ARM.ch06.html#zone_directives">Other Zone File Directives</a></dt>
<dt><a href="Bv9ARM.ch06.html#generate_directive"><acronym class="acronym">BIND</acronym> Master File Extension: the $GENERATE Directive</a></dt>
<dt><a href="Bv9ARM.ch06.html#zonefile_format">Additional File Formats</a></dt>
</dl></dd>
<dt><a href="Bv9ARM.ch06.html#statistics">BIND9 Statistics</a></dt>
<dd><dl>
<dt><a href="Bv9ARM.ch06.html#statsfile">The Statistics File</a></dt>
<dt><a href="Bv9ARM.ch06.html#statistics_counters">Statistics Counters</a></dt>
</dl></dd>
</dl>
</div>

<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.

<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>.
 
 <div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="configuration_file_elements"></a>Configuration File Elements</h2></div></div></div>

Following is a list of elements used throughout the <acronym class="acronym">BIND</acronym> configuration
 file documentation:
 
 <div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.855in" class="1">
<col width="3.770in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 
 <code class="varname">acl_name</code>
 
 </td>
<td>
 
 The name of an <code class="varname">address_match_list</code> as
 defined by the acl statement.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">address_match_list</code>
 
 </td>
<td>
 
 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 class="xref" href="Bv9ARM.ch06.html#address_match_lists" title="Address Match Lists">the section called &#8220;Address Match Lists&#8221;</a>.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">masters_list</code>
 
 </td>
<td>
 
 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>.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">domain_name</code>
 
 </td>
<td>
 
 A quoted string which will be used as
 a DNS name, for example "<code class="literal">my.test.domain</code>".
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">namelist</code>
 
 </td>
<td>
 
 A list of one or more <code class="varname">domain_name</code>
 elements.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">dotted_decimal</code>
 
 </td>
<td>
 
 One to four integers valued 0 through
 255 separated by dots (`.'), such as 123,
 45.67 or 89.123.45.67.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">ip4_addr</code>
 
 </td>
<td>
 
 An IPv4 address with exactly four elements
 in <code class="varname">dotted_decimal</code> notation.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">ip6_addr</code>
 
 </td>
<td>
 
 An IPv6 address, such as 2001:db8::1234.
 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 fe80::1 on the link
 attached to the interface ne0
 can be specified as fe80::1%ne0.
 Note that on most systems link-local addresses
 always have the ambiguity, and need to be
 disambiguated.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">ip_addr</code>
 
 </td>
<td>
 
 An <code class="varname">ip4_addr</code> or <code class="varname">ip6_addr</code>.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">ip_dscp</code>
 
 </td>
<td>
 
 A <code class="varname">number</code> between 0 and 63, used
 to select a differentiated services code point (DSCP)
 value for use with outgoing traffic on operating systems
 that support DSCP.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">ip_port</code>
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">ip_prefix</code>
 
 </td>
<td>
 
 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, 127/8 is the
 network 127.0.0.0 with
 netmask 255.0.0.0 and 1.2.3.0/28 is
 network 1.2.3.0 with netmask 255.255.255.240.
 
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">key_id</code>
 
 </td>
<td>
 
 A <code class="varname">domain_name</code> representing
 the name of a shared key, to be used for transaction
 security.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">key_list</code>
 
 </td>
<td>
 
 A list of one or more
 <code class="varname">key_id</code>s,
 separated by semicolons and ending with a semicolon.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">number</code>
 
 </td>
<td>
 
 A non-negative 32-bit integer
 (i.e., a number between 0 and 4294967295, inclusive).
 Its acceptable value might be further
 limited by the context in which it is used.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">fixedpoint</code>
 
 </td>
<td>
 
 A non-negative real number that can be specified to
 the nearest one hundredth. Up to five digits can be
 specified before a decimal point, and up to two
 digits after, so the maximum value is 99999.99.
 Acceptable values might be further limited by the
 context in which it is used.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">path_name</code>
 
 </td>
<td>
 
 A quoted string which will be used as
 a pathname, such as <code class="filename">zones/master/my.test.domain</code>.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">port_list</code>
 
 </td>
<td>
 
 A list of an <code class="varname">ip_port</code> or a port
 range.
 A port range is specified in the form of
 <code>range</code> 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,
 <code>range 1024 65535</code> represents
 ports from 1024 through 65535.
 In either case an asterisk (`*') character is not
 allowed as a valid <code class="varname">ip_port</code>.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">size_spec</code>
 
 </td>
<td>
 
 A 64-bit unsigned integer, or the keywords
 <code>unlimited</code> or
 <code>default</code>.
 
 
 Integers may take values
 0 &lt;= value &lt;= 18446744073709551615, though
 certain parameters
 (such as max-journal-size) 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.
 
 
 Numeric values can optionally be followed by a
 scaling factor:
 <code>K</code> or <code>k</code>
 for kilobytes,
 <code>M</code> or <code>m</code>
 for megabytes, and
 <code>G</code> or <code>g</code>
 for gigabytes, which scale by 1024, 1024*1024, and
 1024*1024*1024 respectively.
 
 
 <code class="varname">unlimited</code> generally means
 "as big as possible", and is usually the best
 way to safely set a very large number.
 
 
 <code class="varname">default</code>
 uses the limit that was in force when the server was started.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">size_or_percent</code>
 
 </td>
<td>
 
 <code class="varname">size_spec</code> or integer value
 followed by '%' to represent percents.
 
 
 The behavior is exactly the same as
 <code class="varname">size_spec</code>, but
 <code class="varname">size_or_percent</code> allows also
 to specify a positive integer value followed by
 '%' sign to represent percents.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">yes_or_no</code>
 
 </td>
<td>
 
 Either <code>yes</code> or <code>no</code>.
 The words <code>true</code> and <code>false</code> are
 also accepted, as are the numbers <code>1</code>
 and <code>0</code>.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">dialup_option</code>
 
 </td>
<td>
 
 One of <code>yes</code>,
 <code>no</code>, <code>notify</code>,
 <code>notify-passive</code>, <code>refresh</code> or
 <code>passive</code>.
 When used in a zone, <code>notify-passive</code>,
 <code>refresh</code>, and <code>passive</code>
 are restricted to slave and stub zones.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="address_match_lists"></a>Address Match Lists</h3></div></div></div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.7.4.4.2"></a>Syntax</h4></div></div></div>

<pre class="programlisting"><code>address_match_list</code> = <code>address_match_list_element</code> ; ...

<code>address_match_list_element</code> = [ ! ] ( <code>ip_address</code> | <code>ip_prefix</code> |
 key <code>key_id</code> | <code>acl_name</code> | { <code>address_match_list</code> } )
</pre>

</div>
 <div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.7.4.4.3"></a>Definition and Usage</h4></div></div></div>

Address match lists are primarily used to determine access
 control for various server operations. They are also used in
 the listen-on and sortlist
 statements. The elements which constitute an address match
 list can be any of the following:
 
 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
 an IP address (IPv4 or IPv6)
 </li>
<li class="listitem">
 an IP prefix (in `/' notation)
 </li>
<li class="listitem">
 
 a key ID, as defined by the key
 statement
 
 </li>
<li class="listitem">
 the name of an address match list defined with
 the acl statement
 
 </li>
<li class="listitem">
 a nested address match list enclosed in braces
 </li>
</ul></div>

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.

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.

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.

The interpretation of a match depends on whether the list is being
 used for access control, defining listen-on ports, or in a
 sortlist, and whether the element was negated.

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
 allow-notify,
 allow-recursion,
 allow-recursion-on,
 allow-query,
 allow-query-on,
 allow-query-cache,
 allow-query-cache-on,
 allow-transfer,
 allow-update,
 allow-update-forwarding,
 blackhole, and
 keep-response-order all use address match
 lists. Similarly, the listen-on option will cause the
 server to refuse queries on any of the machine's
 addresses which do not match the list.

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
 first 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
 1.2.3/24; ! 1.2.3.13;
 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 ! 1.2.3.13; 1.2.3/24 fixes
 that problem by having 1.2.3.13 blocked by the negation, but
 all other 1.2.3.* hosts fall through.
 
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="comment_syntax"></a>Comment Syntax</h3></div></div></div>

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.

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.7.4.5.3"></a>Syntax</h4></div></div></div>

<pre class="programlisting">/* This is a <acronym class="acronym">BIND</acronym> comment as in C */</pre>

 
<pre class="programlisting">// This is a <acronym class="acronym">BIND</acronym> comment as in C++</pre>

 
<pre class="programlisting"># This is a <acronym class="acronym">BIND</acronym> comment as in common UNIX shells
# and perl</pre>

 
 </div>
 <div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.7.4.5.4"></a>Definition and Usage</h4></div></div></div>

Comments may appear anywhere that whitespace may appear in
 a <acronym class="acronym">BIND</acronym> configuration file.
 
 
 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.
 
 
 C-style comments cannot be nested. For example, the following
 is not valid because the entire comment ends with the first */:

<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>

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:

<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>

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:

<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>

<div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Warning</h3>
 
 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.
 
 </div>
 </div>
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="Configuration_File_Grammar"></a>Configuration File Grammar</h2></div></div></div>

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.

The following statements are supported:

<div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.336in" class="1">
<col width="3.778in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 acl
 </td>
<td>
 
 defines a named IP address
 matching list, for access control and other uses.
 
 </td>
</tr>
<tr>
<td>
 controls
 </td>
<td>
 
 declares control channels to be used
 by the rndc utility.
 
 </td>
</tr>
<tr>
<td>
 include
 </td>
<td>
 
 includes a file.
 
 </td>
</tr>
<tr>
<td>
 key
 </td>
<td>
 
 specifies key information for use in
 authentication and authorization using TSIG.
 
 </td>
</tr>
<tr>
<td>
 logging
 </td>
<td>
 
 specifies what the server logs, and where
 the log messages are sent.
 
 </td>
</tr>
<tr>
<td>
 lwres
 </td>
<td>
 
 configures named to
 also act as a light-weight resolver daemon (lwresd).
 
 </td>
</tr>
<tr>
<td>
 masters
 </td>
<td>
 
 defines a named masters list for
 inclusion in stub and slave zones'
 masters or
 also-notify lists.
 
 </td>
</tr>
<tr>
<td>
 options
 </td>
<td>
 
 controls global server configuration
 options and sets defaults for other statements.
 
 </td>
</tr>
<tr>
<td>
 server
 </td>
<td>
 
 sets certain configuration options on
 a per-server basis.
 
 </td>
</tr>
<tr>
<td>
 statistics-channels
 </td>
<td>
 
 declares communication channels to get access to
 named statistics.
 
 </td>
</tr>
<tr>
<td>
 trusted-keys
 </td>
<td>
 
 defines trusted DNSSEC keys.
 
 </td>
</tr>
<tr>
<td>
 managed-keys
 </td>
<td>
 
 lists DNSSEC keys to be kept up to date
 using RFC 5011 trust anchor maintenance.
 
 </td>
</tr>
<tr>
<td>
 view
 </td>
<td>
 
 defines a view.
 
 </td>
</tr>
<tr>
<td>
 zone
 </td>
<td>
 
 defines a zone.
 
 </td>
</tr>
</tbody>
</table>
 </div>

The logging and
 options statements may only occur once
 per
 configuration.

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="acl_grammar"></a>acl Statement Grammar</h3></div></div></div>
 <pre class="programlisting">
acl <code>string</code> { <code>address_match_element</code>; ... };
</pre>
 </div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="acl"></a>acl Statement Definition and
 Usage</h3></div></div></div>

The acl 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).

The following ACLs are built-in:

<div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.130in" class="1">
<col width="4.000in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 any
 </td>
<td>
 
 Matches all hosts.
 
 </td>
</tr>
<tr>
<td>
 none
 </td>
<td>
 
 Matches no hosts.
 
 </td>
</tr>
<tr>
<td>
 localhost
 </td>
<td>
 
 Matches the IPv4 and IPv6 addresses of all network
 interfaces on the system. When addresses are
 added or removed, the localhost
 ACL element is updated to reflect the changes.
 
 </td>
</tr>
<tr>
<td>
 localnets
 </td>
<td>
 
 Matches any host on an IPv4 or IPv6 network
 for which the system has an interface.
 When addresses are added or removed,
 the localnets
 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, localnets
 only matches the local
 IPv6 addresses, just like localhost.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 </div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="controls_grammar"></a>controls Statement Grammar</h3></div></div></div>
 <pre class="programlisting">
controls {
	inet ( <code>ipv4_address</code> | <code>ipv6_address</code> |
	 * ) [ port ( <code>integer</code> | * ) ] allow
	 { <code>address_match_element</code>; ... } [
	 keys { <code>string</code>; ... } ] [ read-only
	 <code>boolean</code> ];
	unix <code>quoted_string</code> perm <code>integer</code>
	 owner <code>integer</code> group <code>integer</code> [
	 keys { <code>string</code>; ... } ] [ read-only
	 <code>boolean</code> ];
};
</pre>
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="controls_statement_definition_and_usage"></a>controls Statement Definition and
 Usage</h3></div></div></div>

The controls 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 rndc utility to send
 commands to and retrieve non-DNS results from a name server.

An inet control channel is a TCP socket
 listening at the specified ip_port on the
 specified ip_addr, which can be an IPv4 or IPv6
 address. An ip_addr 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 ip_addr of <code class="literal">::</code>.
 If you will only use rndc 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.

If no port is specified, port 953 is used. The asterisk
 "<code class="literal">*</code>" cannot be used for ip_port.

The ability to issue commands over the control channel is
 restricted by the allow and
 keys clauses.
 Connections to the control channel are permitted based on the
 address_match_list. This is for simple
 IP address based filtering only; any key_id
 elements of the address_match_list
 are ignored.

A unix control channel is a UNIX domain
 socket listening at the specified path in the file system.
 Access to the socket is specified by the perm,
 owner and group clauses.
 Note on some platforms (SunOS and Solaris) the permissions
 (perm) are applied to the parent directory
 as the permissions on the socket itself are ignored.

The primary authorization mechanism of the command
 channel is the key_list, which
 contains a list of key_ids.
 Each key_id in the key_list
 is authorized to execute commands over the control channel.
 See <a class="xref" href="Bv9ARM.ch03.html#rndc">Remote Name Daemon Control application</a> in <a class="xref" href="Bv9ARM.ch03.html#admin_tools" title="Administrative Tools">the section called &#8220;Administrative Tools&#8221;</a>)
 for information about configuring keys in rndc.

If the read-only clause is enabled, the
 control channel is limited to the following set of read-only
 commands: nta -dump,
 null, status,
 showzone, testgen, and
 zonestatus. By default,
 read-only is not enabled and the control
 channel allows read-write access.

If no controls statement is present,
 named 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 controls statement
 is present but does not have a keys clause,
 named 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
 <code>rndc-confgen -a</code>.

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 keys 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 rndc work the same way
 ndc worked in BIND 8, simply by executing the
 command <code>rndc-confgen -a</code> after BIND 9 is
 installed.

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
 named is running as) can access it.
 If you
 desire greater flexibility in allowing other users to access
 rndc 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.

To disable the command channel, use an empty
 controls statement:
 controls { };.

</div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="include_grammar"></a>include Statement Grammar</h3></div></div></div>

<pre class="programlisting">include <code>filename</code>;</pre>
 </div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="include_statement"></a>include Statement Definition and Usage</h3></div></div></div>

The include statement inserts the
 specified file at the point where the include
 statement is encountered. The include
 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.

</div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="key_grammar"></a>key Statement Grammar</h3></div></div></div>
 <pre class="programlisting">
key <code>string</code> {
	algorithm <code>string</code>;
	secret <code>string</code>;
};
</pre>
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="key_statement"></a>key Statement Definition and Usage</h3></div></div></div>

The key statement defines a shared
 secret key for use with TSIG (see <a class="xref" href="Bv9ARM.ch04.html#tsig" title="TSIG">the section called &#8220;TSIG&#8221;</a>)
 or the command channel
 (see <a class="xref" href="Bv9ARM.ch06.html#controls_statement_definition_and_usage" title="controls Statement Definition and Usage">the section called &#8220;controls Statement Definition and
 Usage&#8221;</a>).

The key statement can occur at the
 top level
 of the configuration file or inside a view
 statement. Keys defined in top-level key
 statements can be used in all views. Keys intended for use in
 a controls statement
 (see <a class="xref" href="Bv9ARM.ch06.html#controls_statement_definition_and_usage" title="controls Statement Definition and Usage">the section called &#8220;controls Statement Definition and
 Usage&#8221;</a>)
 must be defined at the top level.

The <code>key_id</code>, also known as the
 key name, is a domain name uniquely identifying the key. It can
 be used in a server
 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.

The <code>algorithm_id</code> is a string
 that specifies a security/authentication algorithm. The
 named server 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
 <code>secret_string</code> is the secret
 to be used by the algorithm, and is treated as a Base64
 encoded string.

</div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="logging_grammar"></a>logging Statement Grammar</h3></div></div></div>
 <pre class="programlisting">
logging {
	category <code>string</code> { <code>string</code>; ... };
	channel <code>string</code> {
		buffered <code>boolean</code>;
		file <code>quoted_string</code> [ versions ( "unlimited" | <code>integer</code> )
		 ] [ size <code>size</code> ];
		null;
		print-category <code>boolean</code>;
		print-severity <code>boolean</code>;
		print-time <code>boolean</code>;
		severity <code>log_severity</code>;
		stderr;
		syslog [ <code>syslog_facility</code> ];
	};
};
</pre>
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="logging_statement"></a>logging Statement Definition and Usage</h3></div></div></div>

The logging statement configures a
 wide
 variety of logging options for the name server. Its channel phrase
 associates output methods, format options and severity levels with
 a name that can then be used with the category phrase
 to select how various classes of messages are logged.
 
 
 Only one logging statement is used to
 define
 as many channels and categories as are wanted. If there is no logging statement,
 the logging configuration will be:

<pre class="programlisting">logging {
 category default { default_syslog; default_debug; };
 category unmatched { null; };
};
</pre>

If named is started with the
 <code class="option">-L</code> option, it logs to the specified file
 at startup, instead of using syslog. In this case the logging
 configuration will be:

<pre class="programlisting">logging {
 category default { default_logfile; default_debug; };
 category unmatched { null; };
};
</pre>

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 logging
 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.

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="channel"></a>The channel Phrase</h4></div></div></div>

All log output goes to one or more channels;
 you can make as many of them as you want.

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
 info), and whether to include a
 named-generated time stamp, the
 category name
 and/or severity level (the default is not to include any).

The null destination clause
 causes all messages sent to the channel to be discarded;
 in that case, other options for the channel are meaningless.

The file 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.

If you use the versions log file
 option, then
 named 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 versions unlimited to
 not limit
 the number of versions.
 If a size 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.

The size option for files is used
 to limit log
 growth. If the file ever exceeds the size, then named will
 stop writing to the file unless it has a versions 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
 versions 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.

Example usage of the size and
 versions options:

<pre class="programlisting">channel an_example_channel {
 file "example.log" versions 3 size 20m;
 print-time yes;
 print-category yes;
};
</pre>

The syslog destination clause
 directs the
 channel to the system log. Its argument is a
 syslog facility as described in the syslog man
 page. Known facilities are kern, user,
 mail, daemon, auth,
 syslog, lpr, news,
 uucp, cron, authpriv,
 ftp, local0, local1,
 local2, local3, local4,
 local5, local6 and
 local7, however not all facilities
 are supported on
 all operating systems.
 How syslog will handle messages
 sent to
 this facility is described in the syslog.conf man
 page. If you have a system which uses a very old version of syslog that
 only uses two arguments to the openlog() function,
 then this clause is silently ignored.
 
 
 On Windows machines syslog messages are directed to the EventViewer.
 
 
 The severity clause works like syslog's
 "priorities", except that they can also be used if you are writing
 straight to a file rather than using syslog.
 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.
 
 
 If you are using syslog, then the syslog.conf priorities
 will also determine what eventually passes through. For example,
 defining a channel facility and severity as daemon and debug but
 only logging daemon.warning via syslog.conf will
 cause messages of severity info and
 notice to
 be dropped. If the situation were reversed, with named writing
 messages of only warning or higher,
 then syslogd would
 print all messages it received from the channel.

The stderr 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.

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 named server
 with the <code class="option">-d</code> flag followed by a positive integer,
 or by running rndc trace.
 The global debug level
 can be set to zero, and debugging mode turned off, by running rndc
notrace. 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:

<pre class="programlisting">channel specific_debug_level {
 file "foo";
 severity debug 3;
};
</pre>

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 dynamic
 severity use the
 server's global debug level to determine what messages to print.
 
 
 If print-time has been turned on,
 then
 the date and time will be logged. print-time may
 be specified for a syslog channel,
 but is usually
 pointless since syslog also logs
 the date and
 time. If print-category is
 requested, then the
 category of the message will be logged as well. Finally, if print-severity is
 on, then the severity level of the message will be logged. The print- 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 print- options
 are on:

<code class="computeroutput">28-Feb-2000 15:05:32.863 general: notice: running</code>

If buffered has been turned on the output
 to files will not be flushed after each log entry. By default
 all log messages are flushed.

There are four predefined channels that are used for
 named's default logging as follows.
 If named is started with the
 <code class="option">-L</code> then a
 fifth channel default_logfile is added.
 How they are
 used is described in <a class="xref" href="Bv9ARM.ch06.html#the_category_phrase" title="The category Phrase">the section called &#8220;The category Phrase&#8221;</a>.

<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 '-g' 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;
};

channel default_logfile {
 // this channel is only present if named is
 // started with the -L option, whose argument
 // provides the file name
 file "...";
 // log at the server's current debug level
 severity dynamic;
};
</pre>

The default_debug 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.

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 named has
 changed to the
 new UID, and any debug output generated while named 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">-L</code>
 option to specify a default logfile, or the <code class="option">-g</code>
 option to log to standard error which you can redirect to a file.

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.
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="the_category_phrase"></a>The category Phrase</h4></div></div></div>

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 default category
 instead. If you don't specify a default category, the following
 "default default" is used:

<pre class="programlisting">category default { default_syslog; default_debug; };
</pre>

If you start named with the
 <code class="option">-L</code> option then the default category is:

<pre class="programlisting">category default { default_logfile; default_debug; };
</pre>

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:

<pre class="programlisting">channel my_security_channel {
 file "my_security_file";
 severity info;
};
category security {
 my_security_channel;
 default_syslog;
 default_debug;
};</pre>

To discard all messages in a category, specify the null channel:

<pre class="programlisting">category xfer-out { null; };
category notify { null; };
</pre>

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.
 
 <div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.150in" class="1">
<col width="3.350in" class="2">
</colgroup>
<tbody>
<tr>
<td>
	 client
	</td>
<td>
	 
	 Processing of client requests.
	 
	</td>
</tr>
<tr>
<td>
	 cname
	</td>
<td>
	 
	 Logs nameservers that are skipped due to them being
	 a CNAME rather than A / AAAA records.
	 
	</td>
</tr>
<tr>
<td>
	 config
	</td>
<td>
	 
	 Configuration file parsing and processing.
	 
	</td>
</tr>
<tr>
<td>
	 database
	</td>
<td>
	 
	 Messages relating to the databases used
	 internally by the name server to store zone and cache
	 data.
	 
	</td>
</tr>
<tr>
<td>
	 default
	</td>
<td>
	 
	 The default category defines the logging
	 options for those categories where no specific
	 configuration has been
	 defined.
	 
	</td>
</tr>
<tr>
<td>
	 delegation-only
	</td>
<td>
	 
	 Delegation only. Logs queries that have been
	 forced to NXDOMAIN as the result of a
	 delegation-only zone or a
	 delegation-only in a
	 forward, hint or stub zone declaration.
	 
	</td>
</tr>
<tr>
<td>
	 dispatch
	</td>
<td>
	 
	 Dispatching of incoming packets to the
	 server modules where they are to be processed.
	 
	</td>
</tr>
<tr>
<td>
	 dnssec
	</td>
<td>
	 
	 DNSSEC and TSIG protocol processing.
	 
	</td>
</tr>
<tr>
<td>
	 dnstap
	</td>
<td>
	 
	 The "dnstap" DNS traffic capture system.
	 
	</td>
</tr>
<tr>
<td>
	 edns-disabled
	</td>
<td>
	 
	 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.
	 
	 
	 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.
	 
	 
	 Note: eventually named 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.
	 
	</td>
</tr>
<tr>
<td>
	 general
	</td>
<td>
	 
	 The catch-all. Many things still aren't
	 classified into categories, and they all end up here.
	 
	</td>
</tr>
<tr>
<td>
	 lame-servers
	</td>
<td>
	 
	 Lame servers. These are misconfigurations
	 in remote servers, discovered by BIND 9 when trying to
	 query those servers during resolution.
	 
	</td>
</tr>
<tr>
<td>
	 network
	</td>
<td>
	 
	 Network operations.
	 
	</td>
</tr>
<tr>
<td>
	 notify
	</td>
<td>
	 
	 The NOTIFY protocol.
	 
	</td>
</tr>
<tr>
<td>
	 queries
	</td>
<td>
	 
	 Specify where queries should be logged to.
	 
	 
	 At startup, specifying the category queries will also
	 enable query logging unless querylog option has been
	 specified.

The query log entry first reports a client object
	 identifier in @0x&lt;hexadecimal-number&gt;
	 format. Next, it 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 used along with the EDNS version
	 number (E(#)), if TCP was used (T), if DO
	 (DNSSEC Ok) was set (D), if CD (Checking
	 Disabled) was set (C), if a valid DNS Server
	 COOKIE was received (V), or if a DNS COOKIE
	 option without a valid Server COOKIE was
	 present (K). After this the destination
	 address the query was sent to is reported.

<code class="computeroutput">client 127.0.0.1#62536 (www.example.com): query: www.example.com IN AAAA +SE</code>
	 
	 
	 <code class="computeroutput">client ::1#62537 (www.example.net): query: www.example.net IN AAAA -SE</code>
	 
	 
	 (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.)
	 
	</td>
</tr>
<tr>
<td>
	 query-errors
	</td>
<td>
	 
	 Information about queries that resulted in some
	 failure.
	 
	</td>
</tr>
<tr>
<td>
	 rate-limit
	</td>
<td>
	 
	 The start, periodic, and final notices of the
	 rate limiting of a stream of responses are logged at
	 info 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.
	 
	 
	 Rate limiting of individual requests
	 is logged in the query-errors category.
	 
	</td>
</tr>
<tr>
<td>
	 resolver
	</td>
<td>
	 
	 DNS resolution, such as the recursive
	 lookups performed on behalf of clients by a caching name
	 server.
	 
	</td>
</tr>
<tr>
<td>
	 rpz
	</td>
<td>
	 
	 Information about errors in response policy zone files,
	 rewritten responses, and at the highest
	 debug levels, mere rewriting
	 attempts.
	 
	</td>
</tr>
<tr>
<td>
	 security
	</td>
<td>
	 
	 Approval and denial of requests.
	 
	</td>
</tr>
<tr>
<td>
	 spill
	</td>
<td>
	 
	 Logs queries that have been terminated, either by dropping
	 or responding with SERVFAIL, as a result of a fetchlimit
	 quota being exceeded.
	 
	</td>
</tr>
<tr>
<td>
	 trust-anchor-telemetry
	</td>
<td>
	 
	 Logs trust-anchor-telemetry requests received by named.
	 
	</td>
</tr>
<tr>
<td>
	 unmatched
	</td>
<td>
	 
	 Messages that named was unable to determine the
	 class of or for which there was no matching view.
	 A one line summary is also logged to the client category.
	 This category is best sent to a file or stderr, by
	 default it is sent to
	 the null channel.
	 
	</td>
</tr>
<tr>
<td>
	 update
	</td>
<td>
	 
	 Dynamic updates.
	 
	</td>
</tr>
<tr>
<td>
	 update-security
	</td>
<td>
	 
	 Approval and denial of update requests.
	 
	</td>
</tr>
<tr>
<td>
	 xfer-in
	</td>
<td>
	 
	 Zone transfers the server is receiving.
	 
	</td>
</tr>
<tr>
<td>
	 xfer-out
	</td>
<td>
	 
	 Zone transfers the server is sending.
	 
	</td>
</tr>
</tbody>
</table>
</div>
 </div>
 <div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="query_errors"></a>The query-errors Category</h4></div></div></div>
 
 The query-errors 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 debug levels.

At the debug levels of 1 or higher, each response with the
 rcode of SERVFAIL is logged as follows:
 
 
 <code class="computeroutput">client 127.0.0.1#61502: query failed (SERVFAIL) for www.example.com/IN/AAAA at query.c:3880</code>
 
 
 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.
 
 
 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:

<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>

 
 
 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>.
 
 
 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.
 
 
 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.

<div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.150in" class="1">
<col width="3.350in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 <code class="varname">referral</code>
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 <code class="varname">restart</code>
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 <code class="varname">qrysent</code>
 </td>
<td>
 
 The number of queries the resolver sent at the
 <code class="varname">domain</code> zone.
 
 </td>
</tr>
<tr>
<td>
 <code class="varname">timeout</code>
 </td>
<td>
 
 The number of timeouts since the resolver
 received the last response.
 
 </td>
</tr>
<tr>
<td>
 <code class="varname">lame</code>
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 <code class="varname">neterr</code>
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 <code class="varname">badresp</code>
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 <code class="varname">adberr</code>
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 <code class="varname">findfail</code>
 </td>
<td>
 
 Failures of resolving remote server addresses.
 This is a total number of failures throughout
 the resolution process.
 
 </td>
</tr>
<tr>
<td>
 <code class="varname">valfail</code>
 </td>
<td>
 
 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>.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 
 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.
 
 
 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.
 
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="lwres_grammar"></a>lwres Statement Grammar</h3></div></div></div>

This is the grammar of the lwres
 statement in the <code class="filename">named.conf</code> file:

<pre class="programlisting">lwres {
 [ listen-on {
 ( <code>ip_addr</code> [ port <code>ip_port</code> ] [ dscp <code>ip_dscp</code> ] ; )
 ...
 }; ]
 [ view <code>view_name</code>; ]
 [ search { <code>domain_name</code> ; ... }; ]
 [ ndots <code>number</code>; ]
 [ lwres-tasks <code>number</code>; ]
 [ lwres-clients <code>number</code>; ]
};
</pre>

</div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="lwres_statement"></a>lwres Statement Definition and Usage</h3></div></div></div>

The lwres statement configures the
 name
 server to also act as a lightweight resolver server. (See
 <a class="xref" href="Bv9ARM.ch05.html#lwresd" title="Running a Resolver Daemon">the section called &#8220;Running a Resolver Daemon&#8221;</a>.) There may be multiple
 lwres statements configuring
 lightweight resolver servers with different properties.

The listen-on 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.

The view 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.

The search statement is equivalent to
 the
 search statement in
 <code class="filename">/etc/resolv.conf</code>. It provides a
 list of domains
 which are appended to relative names in queries.

The ndots statement is equivalent to
 the
 ndots 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.
 
 
 The <code class="option">lwres-tasks</code> statement specifies the number
 of worker threads the lightweight resolver will dedicate to serving
 clients. By default the number is the same as the number of CPUs on
 the system; this can be overridden using the <code class="option">-n</code>
 command line option when starting the server.
 
 
 The <code class="option">lwres-clients</code> specifies
 the number of client objects per thread the lightweight
 resolver should create to serve client queries.
 By default, if the lightweight resolver runs as a part
 of named, 256 client objects are
 created for each task; if it runs as lwresd,
 1024 client objects are created for each thread. The maximum
 value is 32768; higher values will be silently ignored and
 the maximum will be used instead.
 Note that setting too high a value may overconsume
 system resources.
 
 
 The maximum number of client queries that the lightweight
 resolver can handle at any one time equals
 <code class="option">lwres-tasks</code> times <code class="option">lwres-clients</code>.
 
 </div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="masters_grammar"></a>masters Statement Grammar</h3></div></div></div>
 <pre class="programlisting">
masters <code>string</code> [ port <code>integer</code> ] [ dscp
 <code>integer</code> ] { ( <code>masters</code> | <code>ipv4_address</code> [
 port <code>integer</code> ] | <code>ipv6_address</code> [ port
 <code>integer</code> ] ) [ key <code>string</code> ]; ... };
</pre>
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="masters_statement"></a>masters Statement Definition and
 Usage</h3></div></div></div>

masters
 lists allow for a common set of masters to be easily used by
 multiple stub and slave zones in their masters
 or also-notify lists.
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="options_grammar"></a>options Statement Grammar</h3></div></div></div>

This is the grammar of the options
 statement in the <code class="filename">named.conf</code> file:
 
 <pre class="programlisting">
options {
	acache-cleaning-interval <code>integer</code>;
	acache-enable <code>boolean</code>;
	additional-from-auth <code>boolean</code>;
	additional-from-cache <code>boolean</code>;
	allow-new-zones <code>boolean</code>;
	allow-notify { <code>address_match_element</code>; ... };
	allow-query { <code>address_match_element</code>; ... };
	allow-query-cache { <code>address_match_element</code>; ... };
	allow-query-cache-on { <code>address_match_element</code>; ... };
	allow-query-on { <code>address_match_element</code>; ... };
	allow-recursion { <code>address_match_element</code>; ... };
	allow-recursion-on { <code>address_match_element</code>; ... };
	allow-transfer { <code>address_match_element</code>; ... };
	allow-update { <code>address_match_element</code>; ... };
	allow-update-forwarding { <code>address_match_element</code>; ... };
	also-notify [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>masters</code> |
	 <code>ipv4_address</code> [ port <code>integer</code> ] | <code>ipv6_address</code> [ port
	 <code>integer</code> ] ) [ key <code>string</code> ]; ... };
	alt-transfer-source ( <code>ipv4_address</code> | * ) [ port ( <code>integer</code> | * )
	 ] [ dscp <code>integer</code> ];
	alt-transfer-source-v6 ( <code>ipv6_address</code> | * ) [ port ( <code>integer</code> |
	 * ) ] [ dscp <code>integer</code> ];
	answer-cookie <code>boolean</code>;
	attach-cache <code>string</code>;
	auth-nxdomain <code>boolean</code>; // default changed
	auto-dnssec ( allow | maintain | off );
	automatic-interface-scan <code>boolean</code>;
	avoid-v4-udp-ports { <code>portrange</code>; ... };
	avoid-v6-udp-ports { <code>portrange</code>; ... };
	bindkeys-file <code>quoted_string</code>;
	blackhole { <code>address_match_element</code>; ... };
	cache-file <code>quoted_string</code>;
	catalog-zones { zone <code>quoted_string</code> [ default-masters [ port
	 <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>masters</code> | <code>ipv4_address</code> [
	 port <code>integer</code> ] | <code>ipv6_address</code> [ port <code>integer</code> ] ) [ key
	 <code>string</code> ]; ... } ] [ zone-directory <code>quoted_string</code> ] [
	 in-memory <code>boolean</code> ] [ min-update-interval <code>integer</code> ]; ... };
	check-dup-records ( fail | warn | ignore );
	check-integrity <code>boolean</code>;
	check-mx ( fail | warn | ignore );
	check-mx-cname ( fail | warn | ignore );
	check-names ( master | slave | response
	 ) ( fail | warn | ignore );
	check-sibling <code>boolean</code>;
	check-spf ( warn | ignore );
	check-srv-cname ( fail | warn | ignore );
	check-wildcard <code>boolean</code>;
	cleaning-interval <code>integer</code>;
	clients-per-query <code>integer</code>;
	cookie-algorithm ( aes | sha1 | sha256 );
	cookie-secret <code>string</code>;
	coresize ( default | unlimited | <code>sizeval</code> );
	datasize ( default | unlimited | <code>sizeval</code> );
	deny-answer-addresses { <code>address_match_element</code>; ... } [
	 except-from { <code>quoted_string</code>; ... } ];
	deny-answer-aliases { <code>quoted_string</code>; ... } [ except-from {
	 <code>quoted_string</code>; ... } ];
	dialup ( notify | notify-passive | passive | refresh | <code>boolean</code> );
	directory <code>quoted_string</code>;
	disable-algorithms <code>string</code> { <code>string</code>;
	 ... };
	disable-ds-digests <code>string</code> { <code>string</code>;
	 ... };
	disable-empty-zone <code>string</code>;
	dns64 <code>netprefix</code> {
		break-dnssec <code>boolean</code>;
		clients { <code>address_match_element</code>; ... };
		exclude { <code>address_match_element</code>; ... };
		mapped { <code>address_match_element</code>; ... };
		recursive-only <code>boolean</code>;
		suffix <code>ipv6_address</code>;
	};
	dns64-contact <code>string</code>;
	dns64-server <code>string</code>;
	dnssec-accept-expired <code>boolean</code>;
	dnssec-dnskey-kskonly <code>boolean</code>;
	dnssec-enable <code>boolean</code>;
	dnssec-loadkeys-interval <code>integer</code>;
	dnssec-lookaside ( <code>string</code> trust-anchor
	 <code>string</code> | auto | no );
	dnssec-must-be-secure <code>string</code> <code>boolean</code>;
	dnssec-secure-to-insecure <code>boolean</code>;
	dnssec-update-mode ( maintain | no-resign );
	dnssec-validation ( yes | no | auto );
	dnstap { ( all | auth | client | forwarder |
	 resolver ) [ ( query | response ) ]; ... };
	dnstap-identity ( <code>quoted_string</code> | none |
	 hostname );
	dnstap-output ( file | unix ) <code>quoted_string</code>;
	dnstap-version ( <code>quoted_string</code> | none );
	dscp <code>integer</code>;
	dual-stack-servers [ port <code>integer</code> ] { ( <code>quoted_string</code> [ port
	 <code>integer</code> ] [ dscp <code>integer</code> ] | <code>ipv4_address</code> [ port
	 <code>integer</code> ] [ dscp <code>integer</code> ] | <code>ipv6_address</code> [ port
	 <code>integer</code> ] [ dscp <code>integer</code> ] ); ... };
	dump-file <code>quoted_string</code>;
	edns-udp-size <code>integer</code>;
	empty-contact <code>string</code>;
	empty-server <code>string</code>;
	empty-zones-enable <code>boolean</code>;
	fetch-quota-params <code>integer</code> <code>fixedpoint</code> <code>fixedpoint</code> <code>fixedpoint</code>;
	fetches-per-server <code>integer</code> [ ( drop | fail ) ];
	fetches-per-zone <code>integer</code> [ ( drop | fail ) ];
	files ( default | unlimited | <code>sizeval</code> );
	filter-aaaa { <code>address_match_element</code>; ... };
	filter-aaaa-on-v4 ( break-dnssec | <code>boolean</code> );
	filter-aaaa-on-v6 ( break-dnssec | <code>boolean</code> );
	flush-zones-on-shutdown <code>boolean</code>;
	forward ( first | only );
	forwarders [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>ipv4_address</code>
	 | <code>ipv6_address</code> ) [ port <code>integer</code> ] [ dscp <code>integer</code> ]; ... };
	fstrm-set-buffer-hint <code>integer</code>;
	fstrm-set-flush-timeout <code>integer</code>;
	fstrm-set-input-queue-size <code>integer</code>;
	fstrm-set-output-notify-threshold <code>integer</code>;
	fstrm-set-output-queue-model ( mpsc | spsc );
	fstrm-set-output-queue-size <code>integer</code>;
	fstrm-set-reopen-interval <code>integer</code>;
	geoip-directory ( <code>quoted_string</code> | none );
	geoip-use-ecs <code>boolean</code>;
	heartbeat-interval <code>integer</code>;
	hostname ( <code>quoted_string</code> | none );
	inline-signing <code>boolean</code>;
	interface-interval <code>integer</code>;
	ixfr-from-differences ( master | slave | <code>boolean</code> );
	keep-response-order { <code>address_match_element</code>; ... };
	key-directory <code>quoted_string</code>;
	lame-ttl <code>ttlval</code>;
	listen-on [ port <code>integer</code> ] [ dscp
	 <code>integer</code> ] {
	 <code>address_match_element</code>; ... };
	listen-on-v6 [ port <code>integer</code> ] [ dscp
	 <code>integer</code> ] {
	 <code>address_match_element</code>; ... };
	lmdb-mapsize <code>sizeval</code>;
	lock-file ( <code>quoted_string</code> | none );
	managed-keys-directory <code>quoted_string</code>;
	masterfile-format ( map | raw | text );
	masterfile-style ( full | relative );
	match-mapped-addresses <code>boolean</code>;
	max-acache-size ( unlimited | <code>sizeval</code> );
	max-cache-size ( default | unlimited | <code>sizeval</code> | <code>percentage</code> );
	max-cache-ttl <code>integer</code>;
	max-clients-per-query <code>integer</code>;
	max-journal-size ( unlimited | <code>sizeval</code> );
	max-ncache-ttl <code>integer</code>;
	max-records <code>integer</code>;
	max-recursion-depth <code>integer</code>;
	max-recursion-queries <code>integer</code>;
	max-refresh-time <code>integer</code>;
	max-retry-time <code>integer</code>;
	max-rsa-exponent-size <code>integer</code>;
	max-transfer-idle-in <code>integer</code>;
	max-transfer-idle-out <code>integer</code>;
	max-transfer-time-in <code>integer</code>;
	max-transfer-time-out <code>integer</code>;
	max-udp-size <code>integer</code>;
	max-zone-ttl ( unlimited | <code>ttlval</code> );
	memstatistics <code>boolean</code>;
	memstatistics-file <code>quoted_string</code>;
	message-compression <code>boolean</code>;
	min-refresh-time <code>integer</code>;
	min-retry-time <code>integer</code>;
	minimal-any <code>boolean</code>;
	minimal-responses ( no-auth | no-auth-recursive | <code>boolean</code> );
	multi-master <code>boolean</code>;
	no-case-compress { <code>address_match_element</code>; ... };
	nocookie-udp-size <code>integer</code>;
	notify ( explicit | master-only | <code>boolean</code> );
	notify-delay <code>integer</code>;
	notify-rate <code>integer</code>;
	notify-source ( <code>ipv4_address</code> | * ) [ port ( <code>integer</code> | * ) ] [
	 dscp <code>integer</code> ];
	notify-source-v6 ( <code>ipv6_address</code> | * ) [ port ( <code>integer</code> | * ) ]
	 [ dscp <code>integer</code> ];
	notify-to-soa <code>boolean</code>;
	nta-lifetime <code>ttlval</code>;
	nta-recheck <code>ttlval</code>;
	nxdomain-redirect <code>string</code>;
	pid-file ( <code>quoted_string</code> | none );
	port <code>integer</code>;
	preferred-glue <code>string</code>;
	prefetch <code>integer</code> [ <code>integer</code> ];
	provide-ixfr <code>boolean</code>;
	query-source ( ( [ address ] ( <code>ipv4_address</code> | * ) [ port (
	 <code>integer</code> | * ) ] ) | ( [ [ address ] ( <code>ipv4_address</code> | * ) ]
	 port ( <code>integer</code> | * ) ) ) [ dscp <code>integer</code> ];
	query-source-v6 ( ( [ address ] ( <code>ipv6_address</code> | * ) [ port (
	 <code>integer</code> | * ) ] ) | ( [ [ address ] ( <code>ipv6_address</code> | * ) ]
	 port ( <code>integer</code> | * ) ) ) [ dscp <code>integer</code> ];
	querylog <code>boolean</code>;
	random-device <code>quoted_string</code>;
	rate-limit {
		all-per-second <code>integer</code>;
		errors-per-second <code>integer</code>;
		exempt-clients { <code>address_match_element</code>; ... };
		ipv4-prefix-length <code>integer</code>;
		ipv6-prefix-length <code>integer</code>;
		log-only <code>boolean</code>;
		max-table-size <code>integer</code>;
		min-table-size <code>integer</code>;
		nodata-per-second <code>integer</code>;
		nxdomains-per-second <code>integer</code>;
		qps-scale <code>integer</code>;
		referrals-per-second <code>integer</code>;
		responses-per-second <code>integer</code>;
		slip <code>integer</code>;
		window <code>integer</code>;
	};
	recursing-file <code>quoted_string</code>;
	recursion <code>boolean</code>;
	recursive-clients <code>integer</code>;
	request-expire <code>boolean</code>;
	request-ixfr <code>boolean</code>;
	request-nsid <code>boolean</code>;
	require-server-cookie <code>boolean</code>;
	reserved-sockets <code>integer</code>;
	resolver-query-timeout <code>integer</code>;
	response-policy { zone <code>quoted_string</code> [ log <code>boolean</code> ] [
	 max-policy-ttl <code>integer</code> ] [ policy ( cname | disabled | drop |
	 given | no-op | nodata | nxdomain | passthru | tcp-only
	 <code>quoted_string</code> ) ] [ recursive-only <code>boolean</code> ]; ... } [
	 break-dnssec <code>boolean</code> ] [ max-policy-ttl <code>integer</code> ] [
	 min-ns-dots <code>integer</code> ] [ nsip-wait-recurse <code>boolean</code> ] [
	 qname-wait-recurse <code>boolean</code> ] [ recursive-only <code>boolean</code> ];
	root-delegation-only [ exclude { <code>quoted_string</code>; ... } ];
	root-key-sentinel <code>boolean</code>;
	rrset-order { [ class <code>string</code> ] [ type <code>string</code> ] [ name
	 <code>quoted_string</code> ] <code>string</code> <code>string</code>; ... };
	secroots-file <code>quoted_string</code>;
	send-cookie <code>boolean</code>;
	serial-query-rate <code>integer</code>;
	serial-update-method ( date | increment | unixtime );
	server-id ( <code>quoted_string</code> | none | hostname );
	servfail-ttl <code>ttlval</code>;
	session-keyalg <code>string</code>;
	session-keyfile ( <code>quoted_string</code> | none );
	session-keyname <code>string</code>;
	sig-signing-nodes <code>integer</code>;
	sig-signing-signatures <code>integer</code>;
	sig-signing-type <code>integer</code>;
	sig-validity-interval <code>integer</code> [ <code>integer</code> ];
	sortlist { <code>address_match_element</code>; ... };
	stacksize ( default | unlimited | <code>sizeval</code> );
	startup-notify-rate <code>integer</code>;
	statistics-file <code>quoted_string</code>;
	tcp-clients <code>integer</code>;
	tcp-listen-queue <code>integer</code>;
	tkey-dhkey <code>quoted_string</code> <code>integer</code>;
	tkey-domain <code>quoted_string</code>;
	tkey-gssapi-credential <code>quoted_string</code>;
	tkey-gssapi-keytab <code>quoted_string</code>;
	transfer-format ( many-answers | one-answer );
	transfer-message-size <code>integer</code>;
	transfer-source ( <code>ipv4_address</code> | * ) [ port ( <code>integer</code> | * ) ] [
	 dscp <code>integer</code> ];
	transfer-source-v6 ( <code>ipv6_address</code> | * ) [ port ( <code>integer</code> | * )
	 ] [ dscp <code>integer</code> ];
	transfers-in <code>integer</code>;
	transfers-out <code>integer</code>;
	transfers-per-ns <code>integer</code>;
	trust-anchor-telemetry <code>boolean</code>; // experimental
	try-tcp-refresh <code>boolean</code>;
	update-check-ksk <code>boolean</code>;
	use-alt-transfer-source <code>boolean</code>;
	use-v4-udp-ports { <code>portrange</code>; ... };
	use-v6-udp-ports { <code>portrange</code>; ... };
	v6-bias <code>integer</code>;
	version ( <code>quoted_string</code> | none );
	zero-no-soa-ttl <code>boolean</code>;
	zero-no-soa-ttl-cache <code>boolean</code>;
	zone-statistics ( full | terse | none | <code>boolean</code> );
};
</pre>
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="options"></a>options Statement Definition and
 Usage</h3></div></div></div>

The options 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 options
 statement, an options block with each option set to its default will
 be used.

<div class="variablelist"><dl class="variablelist">
<dt>attach-cache</dt>
<dd>
 
 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.

The attach-cache option
 may also be specified in view
 statements, in which case it overrides the
 global attach-cache option.

The <code>cache_name</code> specifies
 the cache to be shared.
 When the named 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.

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 attach-cache as a global
 option with an arbitrary name.

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
 attach-cache option as a view A (or
 B)'s option, referring to the other view name:

<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>

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:
 check-names,
 cleaning-interval,
 dnssec-accept-expired,
 dnssec-validation,
 max-cache-ttl,
 max-ncache-ttl,
 max-cache-size, and
 zero-no-soa-ttl.

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.
 
 </dd>
<dt>directory</dt>
<dd>
 
 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. It is
 strongly recommended
 that the directory be writable by the effective user
 ID of the named process.
 
 </dd>
<dt>dnstap</dt>
<dd>
 
 dnstap is a fast, flexible method
 for capturing and logging DNS traffic. Developed by
 Robert Edmonds at Farsight Security, Inc., and supported
 by multiple DNS implementations, dnstap
 uses
 libfstrm (a lightweight high-speed
 framing library, see
 <a class="link" href="https://github.com/farsightsec/fstrm" target="_top">https://github.com/farsightsec/fstrm</a>) to send
 event payloads which are encoded using Protocol Buffers
 (libprotobuf-c, a mechanism for
 serializing structured data developed
 by Google, Inc.; see
 <a class="link" href="https://developers.google.com/protocol-buffers/" target="_top">https://developers.google.com/protocol-buffers</a>).
 
 
 To enable dnstap at compile time,
 the fstrm and protobuf-c
 libraries must be available, and BIND must be configured with
 <code class="option">--enable-dnstap</code>.
 
 
 The dnstap option is a bracketed list
 of message types to be logged. These may be set differently
 for each view. Supported types are <code class="literal">client</code>,
 <code class="literal">auth</code>, <code class="literal">resolver</code>, and
 <code class="literal">forwarder</code>. Specifying type
 <code class="literal">all</code> will cause all dnstap
 messages to be logged, regardless of type.
 
 
 Each type may take an additional argument to indicate whether
 to log <code class="literal">query</code> messages or
 <code class="literal">response</code> messages; if not specified,
 both queries and responses are logged.
 
 
 Example: To log all authoritative queries and responses,
 recursive client responses, and upstream queries sent by
 the resolver, use:

<pre class="programlisting">dnstap {
 auth;
 client response;
 resolver query;
};
</pre>

 
 
 Logged dnstap messages can be parsed
 using the dnstap-read utility (see
 <a class="xref" href="man.dnstap-read.html" title="dnstap-read">dnstap-read(1)</a> for details).
 
 
 For more information on dnstap, see
 <a class="link" href="http://dnstap.info" target="_top">http://dnstap.info</a>.
 
 
 The fstrm library has a number of tunables that are exposed
 in <code class="filename">named.conf</code>, and can be modified
 if necessary to improve performance or prevent loss of data.
 These are:
 
 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
 
 fstrm-set-buffer-hint: The
 threshold number of bytes to accumulate in the output
 buffer before forcing a buffer flush. The minimum is
 1024, the maximum is 65536, and the default is 8192.
 
 </li>
<li class="listitem">
 
 fstrm-set-flush-timeout: The number
 of seconds to allow unflushed data to remain in the
 output buffer. The minimum is 1 second, the maximum is
 600 seconds (10 minutes), and the default is 1 second.
 
 </li>
<li class="listitem">
 
 fstrm-set-output-notify-threshold:
 The number of outstanding queue entries to allow on
 an input queue before waking the I/O thread.
 The minimum is 1 and the default is 32.
 
 </li>
<li class="listitem">
 
 fstrm-set-output-queue-model:
 Controls the queuing semantics to use for queue
 objects. The default is <code class="literal">mpsc</code>
 (multiple producer, single consumer); the other
 option is <code class="literal">spsc</code> (single producer,
 single consumer).
 
 </li>
<li class="listitem">
 
 fstrm-set-input-queue-size: The
 number of queue entries to allocate for each
 input queue. This value must be a power of 2.
 The minimum is 2, the maximum is 16384, and
 the default is 512.
 
 </li>
<li class="listitem">
 
 fstrm-set-output-queue-size:
 The number of queue entries to allocate for each
 output queue. The minimum is 2, the maximum is
 system-dependent and based on <code class="option">IOV_MAX</code>,
 and the default is 64.
 
 </li>
<li class="listitem">
 
 fstrm-set-reopen-interval:
 The number of seconds to wait between attempts to
 reopen a closed output stream. The minimum is 1 second,
 the maximum is 600 seconds (10 minutes), and the default
 is 5 seconds.
 
 </li>
</ul></div>
 
 Note that all of the above minimum, maximum, and default
 values are set by the libfstrm library,
 and may be subject to change in future versions of the
 library. See the libfstrm documentation
 for more information.
 
 </dd>
<dt>dnstap-output</dt>
<dd>
 
 Configures the path to which the dnstap
 frame stream will be sent if dnstap
 is enabled at compile time and active.
 
 
 The first argument is either <code class="literal">file</code> or
 <code class="literal">unix</code>, indicating whether the destination
 is a file or a UNIX domain socket. The second argument
 is the path of the file or socket. (Note: when using a
 socket, dnstap messages will
 only be sent if another process such as
 fstrm_capture
 (provided with libfstrm) is listening on
 the socket.)
 
 
 dnstap-output can only be set globally
 in options. Currently, it can only be
 set once while named is running;
 once set, it cannot be changed by
 rndc reload or
 rndc reconfig.
 
 </dd>
<dt>dnstap-identity</dt>
<dd>
 
 Specifies an identity string to send in
 dnstap messages. If set to
 <code class="literal">hostname</code>, which is the default, the
 server's hostname will be sent. If set to
 <code class="literal">none</code>, no identity string will be sent.
 
 </dd>
<dt>dnstap-version</dt>
<dd>
 
 Specifies a version string to send in
 dnstap messages. The default is the
 version number of the BIND release. If set to
 <code class="literal">none</code>, no version string will be sent.
 
 </dd>
<dt>geoip-directory</dt>
<dd>
 
 Specifies the directory containing GeoIP
 <code class="filename">.dat</code> database files for GeoIP
 initialization. By default, this option is unset
 and the GeoIP support will use libGeoIP's
 built-in directory.
 (For details, see <a class="xref" href="Bv9ARM.ch06.html#acl" title="acl Statement Definition and Usage">the section called &#8220;acl Statement Definition and
 Usage&#8221;</a> about the
 geoip ACL.)
 
 </dd>
<dt>key-directory</dt>
<dd>
 
 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>.)
 
 </dd>
<dt>lmdb-mapsize</dt>
<dd>
 
 When named is built with liblmdb,
 this option sets a maximum size for the memory map of
 the new-zone database (NZD) in LMDB database format.
 This database is used to store configuration information
 for zones added using rndc addzone.
 Note that this is not the NZD database file size, but
 the largest size that the database may grow to.
 
 
 Because the database file is memory mapped, its size is
 limited by the address space of the named process. The
 default of 32 megabytes was chosen to be usable with
 32-bit named builds. The largest
 permitted value is 1 terabyte. Given typical zone
 configurations without elaborate ACLs, a 32 MB NZD file
 ought to be able to hold configurations of about 100,000
 zones.
 
 </dd>
<dt>managed-keys-directory</dt>
<dd>
 
 Specifies the directory in which to store the files that
 track managed DNSSEC keys. By default, this is the working
 directory. The directory must
 be writable by the effective user ID of the
 named process.
 
 
 If named 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 view name
 (or, if it contains characters that are incompatible with
 use as a file name, the SHA256 hash of the view name),
 followed by the extension
 <code class="filename">.mkeys</code>.
 
 
 (Note: in previous releases, file names for views
 always used the SHA256 hash of the view name. To ensure
 compatibility after upgrade, if a file using the old
 name format is found to exist, it will be used instead
 of the new format.)
 
 </dd>
<dt>named-xfer</dt>
<dd>
 
 This option is obsolete. It
 was used in <acronym class="acronym">BIND</acronym> 8 to specify
 the pathname to the named-xfer
 program. In <acronym class="acronym">BIND</acronym> 9, no separate
 named-xfer program is needed;
 its functionality is built into the name server.
 
 </dd>
<dt>tkey-gssapi-keytab</dt>
<dd>
 
 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.
 
 </dd>
<dt>tkey-gssapi-credential</dt>
<dd>
 
 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 "<code>DNS/</code><code class="varname">server.domain</code>".
 To use GSS-TSIG, tkey-domain must
 also be set if a specific keytab is not set with
 tkey-gssapi-keytab.
 
 </dd>
<dt>tkey-domain</dt>
<dd>
 
 The domain appended to the names of all shared keys
 generated with TKEY. When a
 client requests a TKEY 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 domainname
 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.
 
 </dd>
<dt>tkey-dhkey</dt>
<dd>
 
 The Diffie-Hellman key used by the server
 to generate shared keys with clients using the Diffie-Hellman
 mode
 of TKEY. The server must be
 able to load the
 public and private keys from files in the working directory.
 In
 most cases, the <code class="varname">key_name</code> should be the server's host name.
 
 </dd>
<dt>cache-file</dt>
<dd>
 
 This is for testing only. Do not use.
 
 </dd>
<dt>dump-file</dt>
<dd>
 
 The pathname of the file the server dumps
 the database to when instructed to do so with
 rndc dumpdb.
 If not specified, the default is <code class="filename">named_dump.db</code>.
 
 </dd>
<dt>memstatistics-file</dt>
<dd>
 
 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>.
 
 </dd>
<dt>lock-file</dt>
<dd>
 
 The pathname of a file on which named will
 attempt to acquire a file lock when starting up for
 the first time; if unsuccessful, the server will
 will terminate, under the assumption that another
 server is already running. If not specified, the default is
 <code class="filename">/var/run/named/named.lock</code>.
 
 
 Specifying lock-file none disables the
 use of a lock file. lock-file is
 ignored if named was run using the <code class="option">-X</code>
 option, which overrides it. Changes to
 lock-file are ignored if
 named is being reloaded or
 reconfigured; it is only effective when the server is
 first started up.
 
 </dd>
<dt>pid-file</dt>
<dd>
 
 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 pid-file none disables the
 use of a PID file &#8212; no file will be written and any
 existing one will be removed. Note that none
 is a keyword, not a filename, and therefore is not enclosed
 in
 double quotes.
 
 </dd>
<dt>recursing-file</dt>
<dd>
 
 The pathname of the file the server dumps
 the queries that are currently recursing when instructed
 to do so with rndc recursing.
 If not specified, the default is <code class="filename">named.recursing</code>.
 
 </dd>
<dt>statistics-file</dt>
<dd>
 
 The pathname of the file the server appends statistics
 to when instructed to do so using rndc stats.
 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 class="xref" href="Bv9ARM.ch06.html#statsfile" title="The Statistics File">the section called &#8220;The Statistics File&#8221;</a>.
 
 </dd>
<dt>bindkeys-file</dt>
<dd>
 
 The pathname of a file to override the built-in trusted
 keys provided by named.
 See the discussion of dnssec-validation
 for details. If not specified, the default is
 <code class="filename">/etc/bind.keys</code>.
 
 </dd>
<dt>secroots-file</dt>
<dd>
 
 The pathname of the file the server dumps
 security roots to when instructed to do so with
 rndc secroots.
 If not specified, the default is
 <code class="filename">named.secroots</code>.
 
 </dd>
<dt>session-keyfile</dt>
<dd>
 
 The pathname of the file into which to write a TSIG
 session key generated by named for use by
 nsupdate -l. If not specified, the
 default is <code class="filename">/var/run/named/session.key</code>.
 (See <a class="xref" 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
 update-policy statement's
 <code>local</code> option for more
 information about this feature.)
 
 </dd>
<dt>session-keyname</dt>
<dd>
 
 The key name to use for the TSIG session key.
 If not specified, the default is "local-ddns".
 
 </dd>
<dt>session-keyalg</dt>
<dd>
 
 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.
 
 </dd>
<dt>port</dt>
<dd>
 
 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.
 
 </dd>
<dt>dscp</dt>
<dd>
 
 The global Differentiated Services Code Point (DSCP)
 value to classify outgoing DNS traffic on operating
 systems that support DSCP. Valid values are 0 through 63.
 It is not configured by default.
 
 </dd>
<dt>random-device</dt>
<dd>
 
 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
 random-device option takes
 effect during
 the initial configuration load at server startup time and
 is ignored on subsequent reloads.
 
 </dd>
<dt>preferred-glue</dt>
<dd>
 
 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 to prefer A records when responding
 to queries that arrived via IPv4 and AAAA when
 responding to queries that arrived via IPv6.
 
 </dd>
<dt>
<a name="root_delegation_only"></a>root-delegation-only
</dt>
<dd>
 
 Turn on enforcement of delegation-only in TLDs
 (top level domains) and root zones with an optional
 exclude list.
 
 
 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.
 
 
 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.
 
 
 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.
 
 
 Note some TLDs are not delegation only (e.g. "DE", "LV",
 "US" and "MUSEUM"). This list is not exhaustive.

<pre class="programlisting">
options {
 root-delegation-only exclude { "de"; "lv"; "us"; "museum"; };
};
</pre>

</dd>
<dt>disable-algorithms</dt>
<dd>
 
 Disable the specified DNSSEC algorithms at and below the
 specified name.
 Multiple disable-algorithms
 statements are allowed.
 Only the best match disable-algorithms
 clause will be used to determine which algorithms are used.
 
 
 If all supported algorithms are disabled, the zones covered
 by the disable-algorithms will be treated
 as insecure.
 
 </dd>
<dt>disable-ds-digests</dt>
<dd>
 
 Disable the specified DS/DLV digest types at and below the
 specified name.
 Multiple disable-ds-digests
 statements are allowed.
 Only the best match disable-ds-digests
 clause will be used to determine which digest types are used.
 
 
 If all supported digest types are disabled, the zones covered
 by the disable-ds-digests will be treated
 as insecure.
 
 </dd>
<dt>dnssec-lookaside</dt>
<dd>
 
 When set, dnssec-lookaside 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
 dnssec-lookaside, 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.
 
 
 If dnssec-lookaside is set to
 <code>no</code>, then dnssec-lookaside
 is not used.
 
 
 NOTE: The ISC-provided DLV service at
 <code class="literal">dlv.isc.org</code>, has been shut down.
 The dnssec-lookaside auto;
 configuration option, which set named
 up to use ISC DLV with minimal configuration, has
 accordingly been removed.
 
 </dd>
<dt>dnssec-must-be-secure</dt>
<dd>
 
 Specify hierarchies which must be or may not be secure
 (signed and validated). If <code>yes</code>,
 then named will only accept answers if
 they are secure. If <code>no</code>, then normal
 DNSSEC validation applies allowing for insecure answers to
 be accepted. The specified domain must be under a
 trusted-keys or
 managed-keys statement, or
 dnssec-validation auto must be active.
 
 </dd>
<dt>dns64</dt>
<dd>
 
 This directive instructs named 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
 dns64 defines one DNS64 prefix.
 Multiple DNS64 prefixes can be defined.
 
 
 Compatible IPv6 prefixes have lengths of 32, 40, 48, 56,
 64 and 96 as per RFC 6052.
 
 
 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. dns64-server and
 dns64-contact 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.
 
 
 Each dns64 supports an optional
 clients ACL that determines which
 clients are affected by this directive. If not defined,
 it defaults to <code>any;</code>.
 
 
 Each dns64 supports an optional
 mapped ACL that selects which
 IPv4 addresses are to be mapped in the corresponding
 A RRset. If not defined it defaults to
 <code>any;</code>.
 
 
 Normally, DNS64 won't apply to a domain name that
 owns one or more AAAA records; these records will
 simply be returned. The optional
 exclude 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, exclude
 defaults to ::ffff:0.0.0.0/96.
 
 
 A optional suffix can also
 be defined to set the bits trailing the mapped
 IPv4 address bits. By default these bits are
 set to <code>::</code>. The bits
 matching the prefix and mapped IPv4 address
 must be zero.
 
 
 If recursive-only is set to
 yes the DNS64 synthesis will
 only happen for recursive queries. The default
 is no.
 
 
 If break-dnssec is set to
 yes the DNS64 synthesis will
 happen even if the result, if validated, would
 cause a DNSSEC validation failure. If this option
 is set to no (the default), the DO
 is set on the incoming query, and there are RRSIGs on
 the applicable records, then synthesis will not happen.
 
<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>dnssec-loadkeys-interval</dt>
<dd>
 
 When a zone is configured with auto-dnssec
 maintain; 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 class="xref" href="man.dnssec-keygen.html" title="dnssec-keygen">dnssec-keygen(8)</a> and
 <a class="xref" href="man.dnssec-settime.html" title="dnssec-settime">dnssec-settime(8)</a>). The
 dnssec-loadkeys-interval 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.
 
 </dd>
<dt>dnssec-update-mode</dt>
<dd>
 
 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 class="xref" href="Bv9ARM.ch06.html#dynamic_update_policies" title="Dynamic Update Policies">the section called &#8220;Dynamic Update Policies&#8221;</a>), and
 if named has access to the
 private signing key(s) for the zone, then
 named will automatically sign all new
 or changed records and maintain signatures for the zone
 by regenerating RRSIG records whenever they approach
 their expiration date.
 
 
 If the option is changed to <code class="literal">no-resign</code>,
 then named will sign all new or
 changed records, but scheduled maintenance of
 signatures is disabled.
 
 
 With either of these settings, named
 will reject updates to a DNSSEC-signed zone when the
 signing keys are inactive or unavailable to
 named. (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.)
 
 </dd>
<dt>nta-lifetime</dt>
<dd>
 
 Species the default lifetime, in seconds,
 that will be used for negative trust anchors added
 via rndc nta.
 
 
 A negative trust anchor selectively disables
 DNSSEC validation for zones that are known to be
 failing because of misconfiguration rather than
 an attack. When data to be validated is
 at or below an active NTA (and above any other
 configured trust anchors), named will
 abort the DNSSEC validation process and treat the data as
 insecure rather than bogus. This continues until the
 NTA's lifetime is elapsed. NTAs persist
 across named restarts.
 
 
 For convenience, TTL-style time unit suffixes can be
 used to specify the NTA lifetime in seconds, minutes
 or hours. <code class="option">nta-lifetime</code> defaults to
 one hour. It cannot exceed one week.
 
 </dd>
<dt>nta-recheck</dt>
<dd>
 
 Species how often to check whether negative
 trust anchors added via rndc nta
 are still necessary.
 
 
 A negative trust anchor is normally used when a
 domain has stopped validating due to operator error;
 it temporarily disables DNSSEC validation for that
 domain. In the interest of ensuring that DNSSEC
 validation is turned back on as soon as possible,
 named will periodically send a
 query to the domain, ignoring negative trust anchors,
 to find out whether it can now be validated. If so,
 the negative trust anchor is allowed to expire early.
 
 
 Validity checks can be disabled for an individual
 NTA by using rndc nta -f, or
 for all NTAs by setting <code class="option">nta-recheck</code>
 to zero.
 
 
 For convenience, TTL-style time unit suffixes can be
 used to specify the NTA recheck interval in seconds,
 minutes or hours. The default is five minutes. It
 cannot be longer than <code class="option">nta-lifetime</code>
 (which cannot be longer than a week).
 
 </dd>
<dt>max-zone-ttl</dt>
<dd>
 
 Specifies a maximum permissible TTL value in seconds.
 For convenience, TTL-style time unit suffixes may be
 used to specify the maximum value.
 When loading a zone file using a
 <code class="option">masterfile-format</code> of
 <code class="constant">text</code> or <code class="constant">raw</code>,
 any record encountered with a TTL higher than
 <code class="option">max-zone-ttl</code> will cause the zone to
 be rejected.
 
 
 This is useful in DNSSEC-signed zones because when
 rolling to a new DNSKEY, the old key needs to remain
 available until RRSIG records have expired from
 caches. The <code class="option">max-zone-ttl</code> option guarantees
 that the largest TTL in the zone will be no higher
 than the set value.
 
 
 (NOTE: Because <code class="constant">map</code>-format files
 load directly into memory, this option cannot be
 used with them.)
 
 
 The default value is <code class="constant">unlimited</code>.
 A <code class="option">max-zone-ttl</code> of zero is treated as
 <code class="constant">unlimited</code>.
 
 </dd>
<dt>serial-update-method</dt>
<dd>
 
 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.
 
 
 With the default setting of
 serial-update-method increment;, the
 SOA serial number will be incremented by one each time
 the zone is updated.
 
 
 When set to
 serial-update-method unixtime;, 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.
 
 
 When set to
 serial-update-method date;, the
 new SOA serial number will be the current date
 in the form "YYYYMMDD", followed by two zeroes,
 unless the existing serial number is already greater
 than or equal to that value, in which case it is
 incremented by one.
 
 </dd>
<dt>zone-statistics</dt>
<dd>
 
 If <code>full</code>, the server will collect
 statistical data on all zones (unless specifically
 turned off on a per-zone basis by specifying
 zone-statistics terse or
 zone-statistics none
 in the zone statement).
 The default is <code>terse</code>, providing
 minimal statistics on zones (including name and
 current serial number, but not query type
 counters).
 
 
 These statistics may be accessed via the
 statistics-channel or
 using rndc stats, which
 will dump them to the file listed
 in the statistics-file. See
 also <a class="xref" href="Bv9ARM.ch06.html#statsfile" title="The Statistics File">the section called &#8220;The Statistics File&#8221;</a>.
 
 
 For backward compatibility with earlier versions
 of BIND 9, the zone-statistics
 option can also accept <code>yes</code>
 or <code>no</code>; <code>yes</code>
 has the same meaning as <code>full</code>.
 As of <acronym class="acronym">BIND</acronym> 9.10,
 <code>no</code> has the same meaning
 as <code>none</code>; previously, it
 was the same as <code>terse</code>.
 
 </dd>
</dl></div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="boolean_options"></a>Boolean Options</h4></div></div></div>

<div class="variablelist"><dl class="variablelist">
<dt>automatic-interface-scan</dt>
<dd>
 
 If <code>yes</code> and supported by the OS,
 automatically rescan network interfaces when the interface
 addresses are added or removed. The default is
 <code>yes</code>.
 
 
 Currently the OS needs to support routing sockets for
 automatic-interface-scan to be
 supported.
 
 </dd>
<dt>allow-new-zones</dt>
<dd>
 
 If <code>yes</code>, then zones can be
 added at runtime via rndc addzone.
 The default is <code>no</code>.
 
 
 Newly added zones' configuration parameters
 are stored so that they can persist after the
 server is restarted. The configuration information
 is saved in a file called
 <code class="filename"><code>viewname</code>.nzf</code>
 (or, if named is compiled with
 liblmdb, in an LMDB database file called
 <code class="filename"><code>viewname</code>.nzd</code>).
 <code>viewname</code> is the name of the
 view, unless the view name contains characters that are
 incompatible with use as a file name, in which case a
 cryptographic hash of the view name is used instead.
 
 
 Zones added at runtime will have their configuration
 stored either in a new-zone file (NZF) or a new-zone
 database (NZD) depending on whether
 named was linked with
 liblmdb at compile time.
 See <a class="xref" href="man.rndc.html" title="rndc">rndc(8)</a> for further details
 about rndc addzone.
 
 </dd>
<dt>auth-nxdomain</dt>
<dd>
 
 If <code>yes</code>, then the AA bit
 is always set on NXDOMAIN responses, even if the server is
 not actually
 authoritative. The default is <code>no</code>;
 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 <code>yes</code>.
 
 </dd>
<dt>deallocate-on-exit</dt>
<dd>
 
 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.
 
 </dd>
<dt>memstatistics</dt>
<dd>
 
 Write memory statistics to the file specified by
 memstatistics-file at exit.
 The default is <code>no</code> unless
 '-m record' is specified on the command line in
 which case it is <code>yes</code>.
 
 </dd>
<dt>dialup</dt>
<dd>
 
 If <code>yes</code>, 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 heartbeat-interval and
 hopefully during the one call. It also suppresses some of
 the normal
 zone maintenance traffic. The default is <code>no</code>.
 
 
 The dialup option
 may also be specified in the view and
 zone statements,
 in which case it overrides the global dialup
 option.
 
 
 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
 notify and also-notify.
 
 
 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
 heartbeat-interval expires in
 addition to sending
 NOTIFY requests.
 
 
 Finer control can be achieved by using
 <code>notify</code> which only sends NOTIFY
 messages,
 <code>notify-passive</code> which sends NOTIFY
 messages and
 suppresses the normal refresh queries, <code>refresh</code>
 which suppresses normal refresh processing and sends refresh
 queries
 when the heartbeat-interval
 expires, and
 <code>passive</code> which just disables normal
 refresh
 processing.

<div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.150in" class="1">
<col width="1.150in" class="2">
<col width="1.150in" class="3">
<col width="1.150in" class="4">
</colgroup>
<tbody>
<tr>
<td>
 
 dialup mode
 
 </td>
<td>
 
 normal refresh
 
 </td>
<td>
 
 heart-beat refresh
 
 </td>
<td>
 
 heart-beat notify
 
 </td>
</tr>
<tr>
<td>
 no (default)
 </td>
<td>
 
 yes
 
 </td>
<td>
 
 no
 
 </td>
<td>
 
 no
 
 </td>
</tr>
<tr>
<td>
 yes
 </td>
<td>
 
 no
 
 </td>
<td>
 
 yes
 
 </td>
<td>
 
 yes
 
 </td>
</tr>
<tr>
<td>
 notify
 </td>
<td>
 
 yes
 
 </td>
<td>
 
 no
 
 </td>
<td>
 
 yes
 
 </td>
</tr>
<tr>
<td>
 refresh
 </td>
<td>
 
 no
 
 </td>
<td>
 
 yes
 
 </td>
<td>
 
 no
 
 </td>
</tr>
<tr>
<td>
 passive
 </td>
<td>
 
 no
 
 </td>
<td>
 
 no
 
 </td>
<td>
 
 no
 
 </td>
</tr>
<tr>
<td>
 notify-passive
 </td>
<td>
 
 no
 
 </td>
<td>
 
 no
 
 </td>
<td>
 
 yes
 
 </td>
</tr>
</tbody>
</table>
 </div>

Note that normal NOTIFY processing is not affected by
 dialup.

</dd>
<dt>fake-iquery</dt>
<dd>
 
 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.
 
 </dd>
<dt>fetch-glue</dt>
<dd>
 
 This option is obsolete.
 In BIND 8, <code>fetch-glue yes</code>
 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.
 
 </dd>
<dt>flush-zones-on-shutdown</dt>
<dd>
 
 When the nameserver exits due receiving SIGTERM,
 flush or do not flush any pending zone writes. The default
 is
 flush-zones-on-shutdown <code>no</code>.
 
 </dd>
<dt>geoip-use-ecs</dt>
<dd>
 
 When BIND is compiled with GeoIP support and configured
 with "geoip" ACL elements, this option indicates whether
 the EDNS Client Subnet option, if present in a request,
 should be used for matching against the GeoIP database.
 The default is
 geoip-use-ecs <code>yes</code>.
 
 </dd>
<dt>has-old-clients</dt>
<dd>
 
 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
 has-old-clients <code>yes</code>, specify
 the two separate options auth-nxdomain <code>yes</code>
 and rfc2308-type1 <code>no</code> instead.
 
 </dd>
<dt>host-statistics</dt>
<dd>
 
 In BIND 8, this enabled keeping of
 statistics for every host that the name server interacts
 with.
 Not implemented in BIND 9.
 
 </dd>
<dt>root-key-sentinel</dt>
<dd>
 
 Respond to root key sentinel probes as described in
 draft-ietf-dnsop-kskroll-sentinel-08. The default is
 <code>yes</code>.
 
 </dd>
<dt>maintain-ixfr-base</dt>
<dd>
 
 This option is obsolete.
 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 provide-ixfr <code>no</code>.
 
 </dd>
<dt>message-compression</dt>
<dd>
 
 If <code>yes</code>, DNS name compression is
 used in responses to regular queries (not including
 AXFR or IXFR, which always uses compression). Setting
 this option to <code>no</code> reduces CPU
 usage on servers and may improve throughput. However,
 it increases response size, which may cause more queries
 to be processed using TCP; a server with compression
 disabled is out of compliance with RFC 1123 Section
 6.1.3.2. The default is <code>yes</code>.
 
 </dd>
<dt>minimal-responses</dt>
<dd>
 
 If set to <code>yes</code>, 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.
 
 
 When set to <code>no-auth</code>, the
 server will omit records from the authority section
 unless they are required, but it may still add
 records to the additional section. When set to
 <code>no-auth-recursive</code>, this
 is only done if the query is recursive. These
 settings are useful when answering stub clients,
 which usually ignore the authority section.
 <code>no-auth-recursive</code> is
 designed for mixed-mode servers which handle
 both authoritative and recursive queries.
 
 
 The default is <code>no</code>.
 
 </dd>
<dt>minimal-any</dt>
<dd>
 
 If set to <code>yes</code>, then when
 generating a positive response to a query of type
 ANY over UDP, the server will reply with only one
 of the RRsets for the query name, and its covering
 RRSIGs if any, instead of replying with all known
 RRsets for the name. Similarly, a query for type
 RRSIG will be answered with the RRSIG records covering
 only one type. This can reduce the impact of some kinds
 of attack traffic, without harming legitimate
 clients. (Note, however, that the RRset returned is the
 first one found in the database; it is not necessarily
 the smallest available RRset.)
 Additionally, <code class="option">minimal-responses</code> is
 turned on for these queries, so no unnecessary records
 will be added to the authority or additional sections.
 The default is <code>no</code>.
 
 </dd>
<dt>multiple-cnames</dt>
<dd>
 
 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.
 
 </dd>
<dt>notify</dt>
<dd>
 
 If <code>yes</code> (the default),
 DNS NOTIFY messages are sent when a zone the server is
 authoritative for
 changes, see <a class="xref" 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
 also-notify option.
 
 
 If <code>master-only</code>, notifies are only
 sent
 for master zones.
 If <code>explicit</code>, notifies are sent only
 to
 servers explicitly listed using also-notify.
 If <code>no</code>, no notifies are sent.
 
 
 The notify option may also be
 specified in the zone
 statement,
 in which case it overrides the options notify statement.
 It would only be necessary to turn off this option if it
 caused slaves
 to crash.
 
 </dd>
<dt>notify-to-soa</dt>
<dd>
 
 If <code>yes</code> 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.
 
 </dd>
<dt>recursion</dt>
<dd>
 
 If <code>yes</code>, 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
 <code>yes</code>.
 Note that setting recursion no 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.
 
 </dd>
<dt>request-nsid</dt>
<dd>
 
 If <code>yes</code>, 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 resolver category at level
 info.
 The default is <code>no</code>.
 
 </dd>
<dt>request-sit</dt>
<dd>
 
 This experimental option is obsolete.
 
 </dd>
<dt>require-server-cookie</dt>
<dd>
 
 Require a valid server cookie before sending a full
 response to a UDP request from a cookie aware client.
 BADCOOKIE is sent if there is a bad or no existent
 server cookie.
 
 </dd>
<dt>answer-cookie</dt>
<dd>
 
 When set to the default value of <code>yes</code>,
 COOKIE EDNS options will be sent when applicable in
 replies to client queries. If set to
 <code>no</code>, COOKIE EDNS options will not
 be sent in replies. This can only be set at the global
 options level, not per-view.
 
 
 answer-cookie no is only intended as a
 temporary measure, for use when named
 shares an IP address with other servers that do not yet
 support DNS COOKIE. A mismatch between servers on the
 same address is not expected to cause operational
 problems, but the option to disable COOKIE responses so
 that all servers have the same behavior is provided out
 of an abundance of caution. DNS COOKIE is an important
 security mechanism, and should not be disabled unless
 absolutely necessary.
 
 </dd>
<dt>send-cookie</dt>
<dd>
 
 If <code>yes</code>, then a COOKIE EDNS
 option is sent along with the query. If the
 resolver has previously talked to the server, the
 COOKIE returned in the previous transaction is sent.
 This is used by the server to determine whether
 the resolver has talked to it before. A resolver
 sending the correct COOKIE is assumed not to be an
 off-path attacker sending a spoofed-source query;
 the query is therefore unlikely to be part of a
 reflection/amplification attack, so resolvers
 sending a correct COOKIE option are not subject to
 response rate limiting (RRL). Resolvers which
 do not send a correct COOKIE option may be limited
 to receiving smaller responses via the
 nocookie-udp-size option.
 
 </dd>
<dt>nocookie-udp-size</dt>
<dd>
 
 Sets the maximum size of UDP responses that will be
 sent to queries without a valid server COOKIE. A value
 below 128 will be silently raised to 128. The default
 value is 4096, but the max-udp-size
 option may further limit the response size.
 
 </dd>
<dt>sit-secret</dt>
<dd>
 
 This experimental option is obsolete.
 
 </dd>
<dt>cookie-algorithm</dt>
<dd>
 
 Set the algorithm to be used when generating the
 server cookie. One of "aes", "sha1" or "sha256".
 The default is "aes" if supported by the cryptographic
 library or otherwise "sha256".
 
 </dd>
<dt>cookie-secret</dt>
<dd>
 
 If set, this is a shared secret used for generating
 and verifying EDNS COOKIE options
 within an anycast cluster. If not set, the system
 will generate a random secret at startup. The
 shared secret is encoded as a hex string and needs
 to be 128 bits for AES128, 160 bits for SHA1 and
 256 bits for SHA256.
 
 
 If there are multiple secrets specified, the first
 one listed in <code class="filename">named.conf</code> is
 used to generate new server cookies. The others
 will only be used to verify returned cookies.
 
 </dd>
<dt>rfc2308-type1</dt>
<dd>
 
 Setting this to <code>yes</code> will
 cause the server to send NS records along with the SOA
 record for negative
 answers. The default is <code>no</code>.
 
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 Not yet implemented in <acronym class="acronym">BIND</acronym>
 9.
 
 </div>
 </dd>
<dt>trust-anchor-telemetry</dt>
<dd>
 
 Causes named to send specially-formed
 queries once per day to domains for which trust anchors
 have been configured via trusted-keys,
 managed-keys, or
 dnssec-validation auto.
 
 
 The query name used for these queries has the
 form "_ta-xxxx(-xxxx)(...)".&lt;domain&gt;, where
 each "xxxx" is a group of four hexadecimal digits
 representing the key ID of a trusted DNSSEC key.
 The key IDs for each domain are sorted smallest
 to largest prior to encoding. The query type is NULL.
 
 
 By monitoring these queries, zone operators will
 be able to see which resolvers have been updated to
 trust a new key; this may help them decide when it
 is safe to remove an old one.
 
 
 The default is <code>yes</code>.
 
 </dd>
<dt>use-id-pool</dt>
<dd>
 
 This option is obsolete.
 <acronym class="acronym">BIND</acronym> 9 always allocates query
 IDs from a pool.
 
 </dd>
<dt>use-ixfr</dt>
<dd>
 
 This option is obsolete.
 If you need to disable IXFR to a particular server or
 servers, see
 the information on the provide-ixfr option
 in <a class="xref" href="Bv9ARM.ch06.html#server_statement_definition_and_usage" title="server Statement Definition and Usage">the section called &#8220;server Statement Definition and
 Usage&#8221;</a>.
 See also
 <a class="xref" href="Bv9ARM.ch04.html#incremental_zone_transfers" title="Incremental Zone Transfers (IXFR)">the section called &#8220;Incremental Zone Transfers (IXFR)&#8221;</a>.
 
 </dd>
<dt>provide-ixfr</dt>
<dd>
 
 See the description of
 provide-ixfr in
 <a class="xref" href="Bv9ARM.ch06.html#server_statement_definition_and_usage" title="server Statement Definition and Usage">the section called &#8220;server Statement Definition and
 Usage&#8221;</a>.
 
 </dd>
<dt>request-ixfr</dt>
<dd>
 
 See the description of
 request-ixfr in
 <a class="xref" href="Bv9ARM.ch06.html#server_statement_definition_and_usage" title="server Statement Definition and Usage">the section called &#8220;server Statement Definition and
 Usage&#8221;</a>.
 
 </dd>
<dt>request-expire</dt>
<dd>
 
 See the description of
 request-expire in
 <a class="xref" href="Bv9ARM.ch06.html#server_statement_definition_and_usage" title="server Statement Definition and Usage">the section called &#8220;server Statement Definition and
 Usage&#8221;</a>.
 
 </dd>
<dt>treat-cr-as-space</dt>
<dd>
 
 This option was used in <acronym class="acronym">BIND</acronym>
 8 to make
 the server treat carriage return ("\r") 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 "\n"
 and NT/DOS "\r\n" newlines
 are always accepted,
 and the option is ignored.
 
 </dd>
<dt>
additional-from-auth, additional-from-cache
</dt>
<dd>

These options control the behavior of an authoritative
 server when
 answering queries which have additional data, or when
 following CNAME
 and DNAME chains.

When both of these options are set to <code>yes</code>
 (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.

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 no
 disables this behavior and makes
 the server only search for additional data in the zone it
 answers from.

These options are intended for use in authoritative-only
 servers, or in authoritative-only views. Attempts to set
 them to no without also
 specifying
 recursion no will cause the
 server to
 ignore the options and log a warning message.

Specifying additional-from-cache no 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.

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 additional-from-cache no
 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.

</dd>
<dt>match-mapped-addresses</dt>
<dd>
 
 If <code>yes</code>, then an
 IPv4-mapped IPv6 address will match any address match
 list entries that match the corresponding IPv4 address.
 
 
 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,
 named now solves this problem
 internally. The use of this option is discouraged.
 
 </dd>
<dt>filter-aaaa-on-v4</dt>
<dd>
 
 This option is only available when
 <acronym class="acronym">BIND</acronym> 9 is compiled with the
 <code>--enable-filter-aaaa</code> 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 <code>no</code>.
 The filter-aaaa-on-v4 option
 may also be specified in view statements
 to override the global filter-aaaa-on-v4
 option.
 
 
 If <code>yes</code>,
 the DNS client is at an IPv4 address, in filter-aaaa,
 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.
 
 
 If <code>break-dnssec</code>,
 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.
 
 
 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.
 
 
 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.
 
 
 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.
 
 </dd>
<dt>filter-aaaa-on-v6</dt>
<dd>
 
 Identical to filter-aaaa-on-v4,
 except it filters AAAA responses to queries from IPv6
 clients instead of IPv4 clients. To filter all
 responses, set both options to <code>yes</code>.
 
 </dd>
<dt>ixfr-from-differences</dt>
<dd>
 
 When <code>yes</code> 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.
 
 
 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.
 
 ixfr-from-differences
 also accepts master and
 slave at the view and options
 levels which causes
 ixfr-from-differences to be enabled for
 all master or
 slave zones respectively.
 It is off by default.
 
 </dd>
<dt>multi-master</dt>
<dd>
 
 This should be set when you have multiple masters for a zone
 and the
 addresses refer to different machines. If <code>yes</code>, named will
 not log
 when the serial number on the master is less than what named
 currently
 has. The default is <code>no</code>.
 
 </dd>
<dt>auto-dnssec</dt>
<dd>
 
 Zones configured for dynamic DNS may use this
 option to allow varying levels of automatic DNSSEC key
 management. There are three possible settings:
 
 
 auto-dnssec allow; permits
 keys to be updated and the zone fully re-signed
 whenever the user issues the command rndc sign
 <code>zonename</code>.
 
 
 auto-dnssec maintain; includes the
 above, but also automatically adjusts the zone's DNSSEC
 keys on schedule, according to the keys' timing metadata
 (see <a class="xref" href="man.dnssec-keygen.html" title="dnssec-keygen">dnssec-keygen(8)</a> and
 <a class="xref" href="man.dnssec-settime.html" title="dnssec-settime">dnssec-settime(8)</a>). The command
 rndc sign
 <code>zonename</code> causes
 named to load keys from the key
 repository and sign the zone with all keys that are
 active.
 rndc loadkeys
 <code>zonename</code> causes
 named 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
 rndc loadkeys is used. The recheck
 interval is defined by
 dnssec-loadkeys-interval.)
 
 
 The default setting is auto-dnssec off.
 
 </dd>
<dt>dnssec-enable</dt>
<dd>
 
 This indicates whether DNSSEC-related resource
 records are to be returned by named.
 If set to <code>no</code>,
 named will not return DNSSEC-related
 resource records unless specifically queried for.
 The default is <code>yes</code>.
 
 </dd>
<dt>dnssec-validation</dt>
<dd>
 
 Enable DNSSEC validation in named.
 Note dnssec-enable also needs to be
 set to <code>yes</code> to be effective.
 If set to <code>no</code>, DNSSEC validation
 is disabled.
 
 
 If set to <code>auto</code>, DNSSEC validation
 is enabled, and a default trust anchor for the DNS root
 zone is used. If set to <code>yes</code>,
 DNSSEC validation is enabled, but a trust anchor must be
 manually configured using a trusted-keys
 or managed-keys statement. The default
 is <code>yes</code>.
 
 
 The default root trust anchor is stored in the file
 <code class="filename">bind.keys</code>.
 named will load that key at
 startup if dnssec-validation is
 set to <code class="constant">auto</code>. A copy of the file is
 installed along with BIND 9, and is current as of the
 release date. If the root key expires, a new copy of
 <code class="filename">bind.keys</code> can be downloaded
 from <a class="link" href="https://www.isc.org/bind-keys" target="_top">https://www.isc.org/bind-keys</a>.
 
 
 To prevent problems if <code class="filename">bind.keys</code> is
 not found, the current trust anchor is also compiled in
 to named. Relying on this is not
 recommended, however, as it requires named
 to be recompiled with a new key when the root key expires.)
 
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 named only
 loads the root key from <code class="filename">bind.keys</code>.
 The file cannot be used to store keys for other zones.
 The root key in <code class="filename">bind.keys</code> is ignored
 if dnssec-validation auto is not in
 use.
 
 
 Whenever the resolver sends out queries to an
 EDNS-compliant server, it always sets the DO bit
 indicating it can support DNSSEC responses even if
 dnssec-validation is off.
 
 </div>
 </dd>
<dt>dnssec-accept-expired</dt>
<dd>
 
 Accept expired signatures when verifying DNSSEC signatures.
 The default is <code>no</code>.
 Setting this option to <code>yes</code>
 leaves named vulnerable to
 replay attacks.
 
 </dd>
<dt>querylog</dt>
<dd>
 
 Specify whether query logging should be started when named
 starts.
 If querylog is not specified,
 then the query logging
 is determined by the presence of the logging category queries.
 
 </dd>
<dt>check-names</dt>
<dd>
 
 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
 master zones the default is fail.
 For slave zones the default
 is warn.
 For answers received from the network (response)
 the default is ignore.
 
 
 The rules for legal hostnames and mail domains are derived
 from RFC 952 and RFC 821 as modified by RFC 1123.
 
 check-names
 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).
 
 </dd>
<dt>check-dup-records</dt>
<dd>
 
 Check master zones for records that are treated as different
 by DNSSEC but are semantically equal in plain DNS. The
 default is to warn. Other possible
 values are fail and
 ignore.
 
 </dd>
<dt>check-mx</dt>
<dd>
 
 Check whether the MX record appears to refer to a IP address.
 The default is to warn. Other possible
 values are fail and
 ignore.
 
 </dd>
<dt>check-wildcard</dt>
<dd>
 
 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 (yes) is to check
 for non-terminal wildcards and issue a warning.
 
 </dd>
<dt>check-integrity</dt>
<dd>
 
 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
 named-checkzone).
 For NS records only names below top of zone are
 checked (for out-of-zone names and glue consistency
 checks use named-checkzone).
 The default is yes.
 
 
 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
 check-spf.
 
 </dd>
<dt>check-mx-cname</dt>
<dd>
 
 If check-integrity is set then
 fail, warn or ignore MX records that refer
 to CNAMES. The default is to warn.
 
 </dd>
<dt>check-srv-cname</dt>
<dd>
 
 If check-integrity is set then
 fail, warn or ignore SRV records that refer
 to CNAMES. The default is to warn.
 
 </dd>
<dt>check-sibling</dt>
<dd>
 
 When performing integrity checks, also check that
 sibling glue exists. The default is yes.
 
 </dd>
<dt>check-spf</dt>
<dd>
 
 If check-integrity 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
 warn.
 
 </dd>
<dt>zero-no-soa-ttl</dt>
<dd>
 
 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 yes.
 
 </dd>
<dt>zero-no-soa-ttl-cache</dt>
<dd>
 
 When caching a negative response to a SOA query
 set the TTL to zero.
 The default is no.
 
 </dd>
<dt>update-check-ksk</dt>
<dd>
 
 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.
 
 
 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 dnssec-signzone -z
 command line option.
 
 
 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.
 
 </dd>
<dt>dnssec-dnskey-kskonly</dt>
<dd>
 
 When this option and update-check-ksk
 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
 dnssec-signzone -x command line option.
 
 
 The default is no. If
 update-check-ksk is set to
 <code class="literal">no</code>, this option is ignored.
 
 </dd>
<dt>try-tcp-refresh</dt>
<dd>
 
 Try to refresh the zone using TCP if UDP queries fail.
 For BIND 8 compatibility, the default is
 yes.
 
 </dd>
<dt>dnssec-secure-to-insecure</dt>
<dd>
 
 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 no.
 If set to yes, and if the DNSKEY RRset
 at the zone apex is deleted, all RRSIG and NSEC records
 will be removed from the zone as well.
 
 
 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.)
 
 
 Note that if a zone has been configured with
 auto-dnssec maintain and the
 private keys remain accessible in the key repository,
 then the zone will be automatically signed again the
 next time named is started.
 
 </dd>
</dl></div>

</div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="forwarding"></a>Forwarding</h4></div></div></div>

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.

<div class="variablelist"><dl class="variablelist">
<dt>forward</dt>
<dd>
 
 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.
 
 </dd>
<dt>forwarders</dt>
<dd>
 
 Specifies the IP addresses to be used
 for forwarding. The default is the empty list (no
 forwarding).
 
 </dd>
</dl></div>

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 forward only/first behavior,
 or not forward at all, see <a class="xref" href="Bv9ARM.ch06.html#zone_statement_grammar" title="zone Statement Grammar">the section called &#8220;zone
 Statement Grammar&#8221;</a>.
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="dual_stack"></a>Dual-stack Servers</h4></div></div></div>

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.

<div class="variablelist"><dl class="variablelist">
<dt>dual-stack-servers</dt>
<dd>
 
 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 dual-stack-servers have no effect unless
 access to a transport has been disabled on the command line
 (e.g. named -4).
 
 </dd>
</dl></div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="access_control"></a>Access Control</h4></div></div></div>

Access to the server can be restricted based on the IP address
 of the requesting system. See <a class="xref" 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.

<div class="variablelist"><dl class="variablelist">
<dt>allow-notify</dt>
<dd>
 
 Specifies which hosts are allowed to
 notify this server, a slave, of zone changes in addition
 to the zone masters.
 allow-notify may also be
 specified in the
 zone statement, in which case
 it overrides the
 options allow-notify
 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.
 
 </dd>
<dt>allow-query</dt>
<dd>
 
 Specifies which hosts are allowed to ask ordinary
 DNS questions. allow-query may
 also be specified in the zone
 statement, in which case it overrides the
 options allow-query statement.
 If not specified, the default is to allow queries
 from all hosts.
 
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 allow-query-cache is now
 used to specify access to the cache.
 
 </div>
 </dd>
<dt>allow-query-on</dt>
<dd>
 
 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.
 
 
 Note that allow-query-on is only
 checked for queries that are permitted by
 allow-query. A query must be
 allowed by both ACLs, or it will be refused.
 
 
 allow-query-on may
 also be specified in the zone
 statement, in which case it overrides the
 options allow-query-on statement.
 
 
 If not specified, the default is to allow queries
 on all addresses.
 
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 allow-query-cache is
 used to specify access to the cache.
 
 </div>
 </dd>
<dt>allow-query-cache</dt>
<dd>
 
 Specifies which hosts are allowed to get answers
 from the cache. If allow-query-cache
 is not set then allow-recursion
 is used if set, otherwise allow-query
 is used if set unless recursion no; is
 set in which case none; is used,
 otherwise the default (localnets;
 localhost;) is used.
 
 </dd>
<dt>allow-query-cache-on</dt>
<dd>
 
 Specifies which local addresses can give answers
 from the cache. If not specified, the default is
 to allow cache queries on any address,
 localnets and
 localhost.
 
 </dd>
<dt>allow-recursion</dt>
<dd>
 
 Specifies which hosts are allowed to make recursive
 queries through this server. If
 allow-recursion is not set
 then allow-query-cache is
 used if set, otherwise allow-query
 is used if set, otherwise the default
 (localnets;
 localhost;) is used.
 
 </dd>
<dt>allow-recursion-on</dt>
<dd>
 
 Specifies which local addresses can accept recursive
 queries. If not specified, the default is to allow
 recursive queries on all addresses.
 
 </dd>
<dt>allow-update</dt>
<dd>
 
 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 class="xref" href="Bv9ARM.ch07.html#dynamic_update_security" title="Dynamic Update Security">the section called &#8220;Dynamic Update Security&#8221;</a> for details.
 
 </dd>
<dt>allow-update-forwarding</dt>
<dd>
 
 Specifies which hosts are allowed to
 submit Dynamic DNS updates to slave zones to be forwarded to
 the
 master. The default is <code>{ none; }</code>,
 which
 means that no update forwarding will be performed. To
 enable
 update forwarding, specify
 <code>allow-update-forwarding { any; };</code>.
 Specifying values other than <code>{ none; }</code> or
 <code>{ any; }</code> is usually
 counterproductive, since
 the responsibility for update access control should rest
 with the
 master server, not the slaves.
 
 
 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 class="xref" href="Bv9ARM.ch07.html#dynamic_update_security" title="Dynamic Update Security">the section called &#8220;Dynamic Update Security&#8221;</a>
 for more details.
 
 </dd>
<dt>allow-v6-synthesis</dt>
<dd>
 
 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.
 
 </dd>
<dt>allow-transfer</dt>
<dd>
 
 Specifies which hosts are allowed to
 receive zone transfers from the server. allow-transfer may
 also be specified in the zone
 statement, in which
 case it overrides the options allow-transfer statement.
 If not specified, the default is to allow transfers to all
 hosts.
 
 </dd>
<dt>blackhole</dt>
<dd>
 
 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 <code>none</code>.
 
 </dd>
<dt>filter-aaaa</dt>
<dd>
 
 Specifies a list of addresses to which
 filter-aaaa-on-v4
 and filter-aaaa-on-v6
 apply. The default is <code>any</code>.
 
 </dd>
<dt>keep-response-order</dt>
<dd>
 
 Specifies a list of addresses to which the server
 will send responses to TCP queries in the same order
 in which they were received. This disables the
 processing of TCP queries in parallel. The default
 is <code>none</code>.
 
 </dd>
<dt>no-case-compress</dt>
<dd>
 
 Specifies a list of addresses which require responses
 to use case-insensitive compression. This ACL can be
 used when named 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.
 
 
 If left undefined, the ACL defaults to
 none: 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.
 
 
 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.
 
 
 Case-insensitive compression is always
 used in AXFR and IXFR responses, regardless of whether
 the client matches this ACL.
 
 
 There are circumstances in which named
 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 first 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.
 
 </dd>
<dt>resolver-query-timeout</dt>
<dd>
 
 The amount of time in seconds that 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.
 
 </dd>
</dl></div>

</div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interfaces"></a>Interfaces</h4></div></div></div>

The interfaces and ports that the server will answer queries
 from may be specified using the listen-on option. listen-on 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.
 
 
 Multiple listen-on statements are
 allowed.
 For example,

<pre class="programlisting">listen-on { 5.6.7.8; };
listen-on port 1234 { !1.2.3.4; 1.2/16; };
</pre>

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.

If no listen-on is specified, the
 server will listen on port 53 on all IPv4 interfaces.

The listen-on-v6 option is used to
 specify the interfaces and the ports on which the server will
 listen for incoming queries sent using IPv6. If not specified,
 the server will listen on port 53 on all IPv6 interfaces.

When 
<pre class="programlisting">{ any; }</pre>
 is
 specified
 as the <code class="varname">address_match_list</code> for the
 listen-on-v6 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.

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 listen-on-v6
 will be ignored, with a logged warning.

Multiple listen-on-v6 options can
 be used.
 For example,

<pre class="programlisting">listen-on-v6 { any; };
listen-on-v6 port 1234 { !2001:db8::/32; any; };
</pre>

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.)

To make the server not listen on any IPv6 address, use

<pre class="programlisting">listen-on-v6 { none; };
</pre>

</div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="query_address"></a>Query Address</h4></div></div></div>

If the server doesn't know the answer to a question, it will
 query other name servers. query-source specifies
 the address and port used for such queries. For queries sent over
 IPv6, there is a separate query-source-v6 option.
 If address is * (asterisk) or is omitted,
 a wildcard IP address (INADDR_ANY)
 will be used.

If port is * 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 use-v4-udp-ports (for IPv4)
 and use-v6-udp-ports (for IPv6)
 options, excluding the ranges specified in
 the avoid-v4-udp-ports
 and avoid-v6-udp-ports options, respectively.

The defaults of the query-source and
 query-source-v6 options
 are:

<pre class="programlisting">query-source address * port *;
query-source-v6 address * port *;
</pre>

If use-v4-udp-ports or
 use-v6-udp-ports is unspecified,
 named 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,
 named will use the corresponding system
 default range; otherwise, it will use its own defaults:

<pre class="programlisting">use-v4-udp-ports { range 1024 65535; };
use-v6-udp-ports { range 1024 65535; };
</pre>

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 named is running; the new
 range will automatically be applied when named
 is reloaded.
 It is encouraged to
 configure use-v4-udp-ports and
 use-v6-udp-ports explicitly so that the
 ranges are sufficiently large and are reasonably
 independent from the ranges used by other applications.

Note: the operational configuration
 where named runs may prohibit the use
 of some ports. For example, UNIX systems will not allow
 named 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.

The defaults of the avoid-v4-udp-ports and
 avoid-v6-udp-ports options
 are:

<pre class="programlisting">avoid-v4-udp-ports {};
avoid-v6-udp-ports {};
</pre>

Note: BIND 9.5.0 introduced
 the use-queryport-pool
 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
 query-source or
 query-source-v6 options;
 it implicitly disables the use of randomized port numbers.

<div class="variablelist"><dl class="variablelist">
<dt>use-queryport-pool</dt>
<dd>
 
 This option is obsolete.
 
 </dd>
<dt>queryport-pool-ports</dt>
<dd>
 
 This option is obsolete.
 
 </dd>
<dt>queryport-pool-updateinterval</dt>
<dd>
 
 This option is obsolete.
 
 </dd>
</dl></div>
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 The address specified in the query-source 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.
 
 </div>
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 Solaris 2.5.1 and earlier does not support setting the source
 address for TCP sockets.
 
 </div>
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 See also transfer-source and
 notify-source.
 
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="zone_transfers"></a>Zone Transfers</h4></div></div></div>

<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.

<div class="variablelist"><dl class="variablelist">
<dt>also-notify</dt>
<dd>
 
 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
 also-notify 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
 masters lists can be used.
 
 
 If an also-notify list
 is given in a zone statement,
 it will override
 the options also-notify
 statement. When a zone notify
 statement
 is set to no, the IP
 addresses in the global also-notify list will
 not be sent NOTIFY messages for that zone. The default is
 the empty
 list (no global notification list).
 
 </dd>
<dt>max-transfer-time-in</dt>
<dd>
 
 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).
 
 </dd>
<dt>max-transfer-idle-in</dt>
<dd>
 
 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).
 
 </dd>
<dt>max-transfer-time-out</dt>
<dd>
 
 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).
 
 </dd>
<dt>max-transfer-idle-out</dt>
<dd>
 
 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).
 
 </dd>
<dt>notify-rate</dt>
<dd>
 
 The rate at which NOTIFY requests will be sent
 during normal zone maintenance operations. (NOTIFY
 requests due to initial zone loading are subject
 to a separate rate limit; see below.) 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.
 
 </dd>
<dt>startup-notify-rate</dt>
<dd>
 
 The rate at which NOTIFY requests will be sent
 when the name server is first starting up, or when
 zones have been newly added to the nameserver.
 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.
 
 </dd>
<dt>serial-query-rate</dt>
<dd>
 
 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
 serial-query-rate 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.
 
 </dd>
<dt>serial-queries</dt>
<dd>
 
 In BIND 8, the serial-queries
 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 serial-queries option.
 Instead, it limits the rate at which the queries are sent
 as defined using the serial-query-rate option.
 
 </dd>
<dt>transfer-format</dt>
<dd>

Zone transfers can be sent using two different formats,
 one-answer and
 many-answers.
 The transfer-format option is used
 on the master server to determine which format it sends.
 one-answer uses one DNS message per
 resource record transferred.
 many-answers packs as many resource
 records as possible into a message.
 many-answers 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 many-answers format is also supported by
 recent Microsoft Windows nameservers.
 The default is many-answers.
 transfer-format may be overridden on a
 per-server basis by using the server
 statement.

</dd>
<dt>transfer-message-size</dt>
<dd>
 
 This is an upper bound on the uncompressed size of DNS
 messages used in zone transfers over TCP. If a message
 grows larger than this size, additional messages will be
 used to complete the zone transfer. (Note, however,
 that this is a hint, not a hard limit; if a message
 contains a single resource record whose RDATA does not
 fit within the size limit, a larger message will be
 permitted so the record can be transferred.)
 
 
 Valid values are between 512 and 65535 octets, and any
 values outside that range will be adjusted to the nearest
 value within it. The default is <code class="literal">20480</code>,
 which was selected to improve message compression:
 most DNS messages of this size will compress to less
 than 16536 bytes. Larger messages cannot be compressed
 as effectively, because 16536 is the largest permissible
 compression offset pointer in a DNS message.
 
 
 This option is mainly intended for server testing;
 there is rarely any benefit in setting a value other
 than the default.
 
 </dd>
<dt>transfers-in</dt>
<dd>
 
 The maximum number of inbound zone transfers
 that can be running concurrently. The default value is <code class="literal">10</code>.
 Increasing transfers-in may
 speed up the convergence
 of slave zones, but it also may increase the load on the
 local system.
 
 </dd>
<dt>transfers-out</dt>
<dd>
 
 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>.
 
 </dd>
<dt>transfers-per-ns</dt>
<dd>
 
 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 transfers-per-ns
 may
 speed up the convergence of slave zones, but it also may
 increase
 the load on the remote name server. transfers-per-ns may
 be overridden on a per-server basis by using the transfers phrase
 of the server statement.
 
 </dd>
<dt>transfer-source</dt>
<dd>
 transfer-source
 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
 allow-transfer option for the
 zone being transferred, if one is specified. This
 statement sets the
 transfer-source for all zones,
 but can be overridden on a per-view or per-zone
 basis by including a
 transfer-source statement within
 the view or
 zone block in the configuration
 file.
 
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 Solaris 2.5.1 and earlier does not support setting the
 source address for TCP sockets.
 
 </div>
 </dd>
<dt>transfer-source-v6</dt>
<dd>
 
 The same as transfer-source,
 except zone transfers are performed using IPv6.
 
 </dd>
<dt>alt-transfer-source</dt>
<dd>
 
 An alternate transfer source if the one listed in
 transfer-source fails and
 use-alt-transfer-source is
 set.
 
 <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
 use-alt-transfer-source
 appropriately and you should not depend upon
 getting an answer back to the first refresh
 query.
 
</div>
 </dd>
<dt>alt-transfer-source-v6</dt>
<dd>
 
 An alternate transfer source if the one listed in
 transfer-source-v6 fails and
 use-alt-transfer-source is
 set.
 
 </dd>
<dt>use-alt-transfer-source</dt>
<dd>
 
 Use the alternate transfer sources or not. If views are
 specified this defaults to no
 otherwise it defaults to
 yes (for BIND 8
 compatibility).
 
 </dd>
<dt>notify-source</dt>
<dd>
 notify-source
 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 masters zone clause or
 in an allow-notify clause. This
 statement sets the notify-source
 for all zones, but can be overridden on a per-zone or
 per-view basis by including a
 notify-source statement within
 the zone or
 view block in the configuration
 file.
 
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 Solaris 2.5.1 and earlier does not support setting the
 source address for TCP sockets.
 
 </div>
 </dd>
<dt>notify-source-v6</dt>
<dd>
 
 Like notify-source,
 but applies to notify messages sent to IPv6 addresses.
 
 </dd>
</dl></div>

</div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="port_lists"></a>UDP Port Lists</h4></div></div></div>

use-v4-udp-ports,
 avoid-v4-udp-ports,
 use-v6-udp-ports, and
 avoid-v6-udp-ports
 specify a list of IPv4 and IPv6 UDP ports that will be
 used or not used as source ports for UDP messages.
 See <a class="xref" 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

<pre class="programlisting">
use-v6-udp-ports { range 32768 65535; };
avoid-v6-udp-ports { 40000; range 50000 60000; };
</pre>

UDP ports of IPv6 messages sent
 from named will be in one
 of the following ranges: 32768 to 39999, 40001 to 49999,
 and 60001 to 65535.

avoid-v4-udp-ports and
 avoid-v6-udp-ports can be used
 to prevent named 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
 use-v4-udp-ports and
 use-v6-udp-ports, and the
 avoid- options are redundant in that
 sense; they are provided for backward compatibility and
 to possibly simplify the port specification.
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="resource_limits"></a>Operating System Resource Limits</h4></div></div></div>

The server's usage of many system resources can be limited.
 Scaled values are allowed when specifying resource limits. For
 example, 1G can be used instead of
 1073741824 to specify a limit of
 one
 gigabyte. unlimited requests
 unlimited use, or the
 maximum available amount. default
 uses the limit
 that was in force when the server was started. See the description
 of size_spec in <a class="xref" href="Bv9ARM.ch06.html#configuration_file_elements" title="Configuration File Elements">the section called &#8220;Configuration File Elements&#8221;</a>.

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.

<div class="variablelist"><dl class="variablelist">
<dt>coresize</dt>
<dd>
 
 The maximum size of a core dump. The default
 is <code class="literal">default</code>.
 
 </dd>
<dt>datasize</dt>
<dd>
 
 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
 max-cache-size and
 recursive-clients
 options instead.
 
 </dd>
<dt>files</dt>
<dd>
 
 The maximum number of files the server
 may have open concurrently. The default is <code class="literal">unlimited</code>.
 
 </dd>
<dt>stacksize</dt>
<dd>
 
 The maximum amount of stack memory the server
 may use. The default is <code class="literal">default</code>.
 
 </dd>
</dl></div>

</div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="server_resource_limits"></a>Server Resource Limits</h4></div></div></div>

The following options set limits on the server's
 resource consumption that are enforced internally by the
 server rather than the operating system.

<div class="variablelist"><dl class="variablelist">
<dt>max-ixfr-log-size</dt>
<dd>
 
 This option is obsolete; it is accepted
 and ignored for BIND 8 compatibility. The option
 max-journal-size performs a
 similar function in BIND 9.
 
 </dd>
<dt>max-journal-size</dt>
<dd>
 
 Sets a maximum size for each journal file
 (see <a class="xref" 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.
 
 </dd>
<dt>max-records</dt>
<dd>
 
 The maximum number of records permitted in a zone.
 The default is zero which means unlimited.
 
 </dd>
<dt>host-statistics-max</dt>
<dd>
 
 In BIND 8, specifies the maximum number of host statistics
 entries to be kept.
 Not implemented in BIND 9.
 
 </dd>
<dt>recursive-clients</dt>
<dd>
 
 The maximum number ("hard quota") 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
 recursive-clients option may
 have to be decreased on hosts with limited memory.
 
 
 <code class="option">recursive-clients</code> defines a "hard
 quota" limit for pending recursive clients: when more
 clients than this are pending, new incoming requests
 will not be accepted, and for each incoming request
 a previous pending request will also be dropped.
 
 
 A "soft quota" is also set. When this lower
 quota is exceeded, incoming requests are accepted, but
 for each one, a pending request will be dropped.
 If <code class="option">recursive-clients</code> is greater than
 1000, the soft quota is set to
 <code class="option">recursive-clients</code> minus 100;
 otherwise it is set to 90% of
 <code class="option">recursive-clients</code>.
 
 </dd>
<dt>tcp-clients</dt>
<dd>
 
 The maximum number of simultaneous client TCP
 connections that the server will accept.
 The default is <code class="literal">150</code>.
 
 </dd>
<dt>
<a name="clients-per-query"></a><a name="cpq_term"></a>clients-per-query, max-clients-per-query
</dt>
<dd>
 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. named will attempt to
 self tune this value and changes will be logged. The
 default values are 10 and 100.
 
 
 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, named 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.
 
 
 If clients-per-query is set to zero,
 then there is no limit on the number of clients per query
 and no queries will be dropped.
 
 
 If max-clients-per-query is set to zero,
 then there is no upper bound other than imposed by
 recursive-clients.
 
 </dd>
<dt>
<a name="fetches-per-zone"></a>fetches-per-zone
</dt>
<dd>
 
 The maximum number of simultaneous iterative
 queries to any one domain that the server will
 permit before blocking new queries for data
 in or beneath that zone.
 This value should reflect how many fetches would
 normally be sent to any one zone in the time it
 would take to resolve them. It should be smaller
 than <code class="option">recursive-clients</code>.
 
 
 When many clients simultaneously query for the
 same name and type, the clients will all be attached
 to the same fetch, up to the
 <code class="option">max-clients-per-query</code> limit,
 and only one iterative query will be sent.
 However, when clients are simultaneously
 querying for different names
 or types, multiple queries will be sent and
 <code class="option">max-clients-per-query</code> is not
 effective as a limit.
 
 
 Optionally, this value may be followed by the keyword
 <code class="literal">drop</code> or <code class="literal">fail</code>,
 indicating whether queries which exceed the fetch
 quota for a zone will be dropped with no response,
 or answered with SERVFAIL. The default is
 <code class="literal">drop</code>.
 
 
 If fetches-per-zone is set to zero,
 then there is no limit on the number of fetches per query
 and no queries will be dropped. The default is zero.
 
 
 The current list of active fetches can be dumped by
 running rndc recursing. The list
 includes the number of active fetches for each
 domain and the number of queries that have been
 passed or dropped as a result of the
 <code class="option">fetches-per-zone</code> limit. (Note:
 these counters are not cumulative over time; whenever
 the number of active fetches for a domain drops to
 zero, the counter for that domain is deleted, and the
 next time a fetch is sent to that domain, it is
 recreated with the counters set to zero.)
 
 </dd>
<dt>
<a name="fetches-per-server"></a>fetches-per-server
</dt>
<dd>
 
 The maximum number of simultaneous iterative
 queries that the server will allow to be sent to
 a single upstream name server before blocking
 additional queries.
 This value should reflect how many fetches would
 normally be sent to any one server in the time it
 would take to resolve them. It should be smaller
 than <code class="option">recursive-clients</code>.
 
 
 Optionally, this value may be followed by the keyword
 <code class="literal">drop</code> or <code class="literal">fail</code>,
 indicating whether queries will be dropped with no
 response, or answered with SERVFAIL, when all of the
 servers authoritative for a zone are found to have
 exceeded the per-server quota. The default is
 <code class="literal">fail</code>.
 
 
 If fetches-per-server is set to zero,
 then there is no limit on the number of fetches per query
 and no queries will be dropped. The default is zero.
 
 
 The fetches-per-server quota is
 dynamically adjusted in response to detected
 congestion. As queries are sent to a server
 and are either answered or time out, an
 exponentially weighted moving average is calculated
 of the ratio of timeouts to responses. If the
 current average timeout ratio rises above a "high"
 threshold, then fetches-per-server
 is reduced for that server. If the timeout ratio
 drops below a "low" threshold, then
 fetches-per-server is increased.
 The fetch-quota-params options
 can be used to adjust the parameters for this
 calculation.
 
 </dd>
<dt>fetch-quota-params</dt>
<dd>
 
 Sets the parameters to use for dynamic resizing of
 the <code class="option">fetches-per-server</code> quota in
 response to detected congestion.
 
 
 The first argument is an integer value indicating
 how frequently to recalculate the moving average
 of the ratio of timeouts to responses for each
 server. The default is 100, meaning we recalculate
 the average ratio after every 100 queries have either
 been answered or timed out.
 
 
 The remaining three arguments represent the "low"
 threshold (defaulting to a timeout ratio of 0.1),
 the "high" threshold (defaulting to a timeout
 ratio of 0.3), and the discount rate for
 the moving average (defaulting to 0.7).
 A higher discount rate causes recent events to
 weigh more heavily when calculating the moving
 average; a lower discount rate causes past
 events to weigh more heavily, smoothing out
 short-term blips in the timeout ratio.
 These arguments are all fixed-point numbers with
 precision of 1/100: at most two places after
 the decimal point are significant.
 
 </dd>
<dt>reserved-sockets</dt>
<dd>
 
 The number of file descriptors reserved for TCP, stdio,
 etc. This needs to be big enough to cover the number of
 interfaces named listens on, tcp-clients 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.
 
 
 This option has little effect on Windows.
 
 </dd>
<dt>max-cache-size</dt>
<dd>
 
 The maximum amount of memory to use for the
 server's cache, in bytes or % of total physical memory.
 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.
 The keyword <code>unlimited</code>,
 or the value 0, will place no limit on cache size;
 records will be purged from the cache only when their
 TTLs expire.
 Any positive values less than 2MB will be ignored
 and reset to 2MB.
 In a server with multiple views, the limit applies
 separately to the cache of each view.
 The default is <code>90%</code>.
 On systems where detection of amount of physical
 memory is not supported values represented as %
 fall back to unlimited.
 Note that the detection of physical memory is done only
 once at startup, so named will not
 adjust the cache size if the amount of physical memory
 is changed during runtime.
 
 </dd>
<dt>tcp-listen-queue</dt>
<dd>
 
 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.
 
 </dd>
</dl></div>

</div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="intervals"></a>Periodic Task Intervals</h4></div></div></div>

<div class="variablelist"><dl class="variablelist">
<dt>cleaning-interval</dt>
<dd>
 
 This interval is effectively obsolete. Previously,
 the server would remove expired resource records
 from the cache every cleaning-interval 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.
 
 </dd>
<dt>heartbeat-interval</dt>
<dd>
 
 The server will perform zone maintenance tasks
 for all zones marked as dialup 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.
 
 </dd>
<dt>interface-interval</dt>
<dd>
 
 The server will scan the network interface list
 every interface-interval
 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
 listen-on configuration), and
 will
 stop listening on interfaces that have gone away.
 
 </dd>
<dt>statistics-interval</dt>
<dd>
 
 Name server statistics will be logged
 every statistics-interval
 minutes. The default is
 60. The maximum value is 28 days (40320 minutes).
 If set to 0, no statistics will be logged.
 
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 Not yet implemented in
 <acronym class="acronym">BIND</acronym> 9.
 
 </div>
 </dd>
<dt>topology</dt>
<dd>
 
 In BIND 8, this option indicated network topology
 so that preferential treatment could be given to
 the topologicaly closest name servers when sending
 queries. It is not implemented in BIND 9.
 
 </dd>
</dl></div>

</div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="the_sortlist_statement"></a>The sortlist Statement</h4></div></div></div>

The response to a DNS query may consist of multiple resource
 records (RRs) forming a resource record set (RRset). The name
 server will normally return the RRs within the RRset in an
 indeterminate order (but see the rrset-order
 statement in <a class="xref" 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.

The sortlist statement (see below) takes an
 address_match_list and interprets it in a
 special way. Each top level statement in the
 sortlist must itself be an explicit
 address_match_list with one or two elements.
 The first element (which may be an IP address, an IP prefix, an
 ACL name or a nested address_match_list) of
 each top level list is checked against the source address of
 the query until a match is found.
 
 
 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 interpreted as a topology preference
 list. 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.
 
 
 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.

<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>

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.

<pre class="programlisting">sortlist {
 { localhost; localnets; };
 { localnets; };
};
</pre>

</div>
 <div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="rrset_ordering"></a>RRset Ordering</h4></div></div></div>

When multiple records are returned in an answer it may be
 useful to configure the order of the records placed into the
 response.
 The rrset-order statement permits
 configuration
 of the ordering of the records in a multiple record response.
 See also the sortlist statement,
 <a class="xref" href="Bv9ARM.ch06.html#the_sortlist_statement" title="The sortlist Statement">the section called &#8220;The sortlist Statement&#8221;</a>.

An order_spec is defined as
 follows:
 
 
 [class <code>class_name</code>]
 [type <code>type_name</code>]
 [name <code>"domain_name"</code>]
 order <code>ordering</code>
 
 
 If no class is specified, the default is ANY.
 If no type is specified, the default is ANY.
 If no name is specified, the default is "*" (asterisk).
 
 
 The legal values for ordering are:
 
 <div class="informaltable">
 <table border="1">
<colgroup>
<col width="0.750in" class="1">
<col width="3.750in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 fixed
 </td>
<td>
 
 Records are returned in the order they
 are defined in the zone file.
 
 </td>
</tr>
<tr>
<td>
 random
 </td>
<td>
 
 Records are returned in some random order.
 
 </td>
</tr>
<tr>
<td>
 cyclic
 </td>
<td>
 
 Records are returned in a cyclic round-robin order.
 
 
 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.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 
 For example:

<pre class="programlisting">rrset-order {
 class IN type A name "host.example.com" order random;
 order cyclic;
};
</pre>

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.
 
 
 If multiple rrset-order statements
 appear, they are not combined &#8212; the last one applies.
 
 
 By default, all records are returned in random order.

<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 In this release of <acronym class="acronym">BIND</acronym> 9, the
 rrset-order 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.
 
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="tuning"></a>Tuning</h4></div></div></div>

<div class="variablelist"><dl class="variablelist">
<dt>lame-ttl</dt>
<dd>
 
 Sets the number of seconds to cache a
 lame server indication. 0 disables caching. (This is
 NOT recommended.)
 The default is <code class="literal">600</code> (10 minutes) and the
 maximum value is
 <code class="literal">1800</code> (30 minutes).

</dd>
<dt>servfail-ttl</dt>
<dd>
 
 Sets the number of seconds to cache a
 SERVFAIL response due to DNSSEC validation failure or
 other general server failure. If set to
 <code class="literal">0</code>, SERVFAIL caching is disabled.
 The SERVFAIL cache is not consulted if a query has
 the CD (Checking Disabled) bit set; this allows a
 query that failed due to DNSSEC validation to be retried
 without waiting for the SERVFAIL TTL to expire.
 
 
 The maximum value is <code class="literal">30</code>
 seconds; any higher value will be silently
 reduced. The default is <code class="literal">1</code>
 second.
 
 </dd>
<dt>max-ncache-ttl</dt>
<dd>
 
 To reduce network traffic and increase performance,
 the server stores negative answers. max-ncache-ttl is
 used to set a maximum retention time for these answers in
 the server
 in seconds. The default
 max-ncache-ttl is <code class="literal">10800</code> seconds (3 hours).
 max-ncache-ttl cannot exceed
 7 days and will
 be silently truncated to 7 days if set to a greater value.
 
 </dd>
<dt>max-cache-ttl</dt>
<dd>
 
 Sets the maximum time for which the server will
 cache ordinary (positive) answers in seconds.
 The default is 604800 (one week).
 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.
 
 </dd>
<dt>min-roots</dt>
<dd>
 
 The minimum number of root servers that
 is required for a request for the root servers to be
 accepted. The default
 is <code>2</code>.
 
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 Not implemented in <acronym class="acronym">BIND</acronym> 9.
 
 </div>
 </dd>
<dt>sig-validity-interval</dt>
<dd>
 
 Specifies the number of days into the future when
 DNSSEC signatures automatically generated as a
 result of dynamic updates (<a class="xref" 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).
 
 
 The signature inception time is unconditionally
 set to one hour before the current time to allow
 for a limited amount of clock skew.
 
 
 The sig-validity-interval
 should be, at least, several multiples of the SOA
 expire interval to allow for reasonable interaction
 between the various timer and expiry dates.
 
 </dd>
<dt>sig-signing-nodes</dt>
<dd>
 
 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>.
 
 </dd>
<dt>sig-signing-signatures</dt>
<dd>
 
 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>.
 
 </dd>
<dt>sig-signing-type</dt>
<dd>
 
 Specify a private RDATA type to be used when generating
 signing state records. The default is
 <code class="literal">65534</code>.
 
 
 It is expected that this parameter may be removed
 in a future version once there is a standard type.
 
 
 Signing state records are used to internally by
 named 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
 rndc signing -list <code>zone</code>.
 Once named 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
 rndc signing -clear <code>keyid/algorithm</code> <code>zone</code>.
 To clear all of the completed signing state
 records for a zone, use
 rndc signing -clear all <code>zone</code>.
 
 </dd>
<dt>
min-refresh-time, max-refresh-time, min-retry-time, max-retry-time
</dt>
<dd>
 
 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,
 up to a hard-coded maximum expiry of 24 weeks. However,
 these values are set by the master, giving slave server
 administrators little control over their contents.
 
 
 These options allow the administrator to set a minimum and
 maximum refresh and retry time in seconds 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.
 
 
 The following defaults apply.
 min-refresh-time 300 seconds,
 max-refresh-time 2419200 seconds
 (4 weeks), min-retry-time 500 seconds,
 and max-retry-time 1209600 seconds
 (2 weeks).
 
 </dd>
<dt>edns-udp-size</dt>
<dd>
 
 Sets the maximum advertised EDNS UDP buffer size in
 bytes, to control the size of packets received from
 authoritative servers in response to recursive queries.
 Valid values are 512 to 4096 (values outside this range
 will be silently adjusted to the nearest value within
 it). The default value is 4096.
 
 
 The usual reason for setting
 edns-udp-size to a non-default value
 is to get UDP answers to pass through broken firewalls
 that block fragmented packets and/or block UDP DNS
 packets that are greater than 512 bytes.
 
 
 When named first queries a remote
 server, it will advertise a UDP buffer size of 512, as
 this has the greatest chance of success on the first try.
 
 
 If the initial response times out, named
 will try again with plain DNS, and if that is successful,
 it will be taken as evidence that the server does not
 support EDNS. After enough failures using EDNS and
 successes using plain DNS, named
 will default to plain DNS for future communications
 with that server. (Periodically, named
 will send an EDNS query to see if the situation has
 improved.)
 
 
 However, if the initial query is successful with
 EDNS advertising a buffer size of 512, then
 named will advertise progressively
 larger buffer sizes on successive queries, until
 responses begin timing out or
 edns-udp-size is reached.
 
 
 The default buffer sizes used by named
 are 512, 1232, 1432, and 4096, but never exceeding
 edns-udp-size. (The values 1232 and
 1432 are chosen to allow for an IPv4/IPv6 encapsulated
 UDP message to be sent without fragmentation at the
 minimum MTU sizes for Ethernet and IPv6 networks.)
 
 </dd>
<dt>max-udp-size</dt>
<dd>
 
 Sets the maximum EDNS UDP message size
 named will send in bytes.
 Valid values are 512 to 4096 (values outside this
 range will be silently adjusted to the nearest
 value within it). The default value is 4096.
 
 
 This value applies to responses sent by a server; to
 set the advertised buffer size in queries, see
 edns-udp-size.
 
 
 The usual reason for setting
 max-udp-size 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 (edns-udp-size).
 
 
 Setting this to a low value will encourage additional
 TCP traffic to the nameserver.
 
 </dd>
<dt>masterfile-format</dt>
<dd>
 Specifies
 the file format of zone files (see
 <a class="xref" 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
 named-compilezone tool, or dumped by
 named.
 
 
 Note that when a zone file in a different format than
 <code class="constant">text</code> is loaded, named
 may omit some of the checks which would be performed for a
 file in the <code class="constant">text</code> format. In particular,
 check-names 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 named configuration
 file. Also, <code class="constant">map</code> format files are
 loaded directly into memory via memory mapping, with only
 minimal checking.
 
 
 This statement sets the
 masterfile-format for all zones,
 but can be overridden on a per-zone or per-view basis
 by including a masterfile-format
 statement within the zone or
 view block in the configuration
 file.
 
 </dd>
<dt>masterfile-style</dt>
<dd>
 
 Specifies the formatting of zone files during dump
 when the <code class="option">masterfile-format</code> is
 <code class="constant">text</code>. (This option is ignored
 with any other <code class="option">masterfile-format</code>.)
 
 
 When set to <code class="constant">relative</code>,
 records are printed in a multi-line format with owner
 names expressed relative to a shared origin. When set
 to <code class="constant">full</code>, records are printed in
 a single-line format with absolute owner names.
 The <code class="constant">full</code> format is most suitable
 when a zone file needs to be processed automatically
 by a script. The <code class="constant">relative</code> format
 is more human-readable, and is thus suitable when a
 zone is to be edited by hand. The default is
 <code class="constant">relative</code>.
 
 </dd>
<dt>
<a name="max-recursion-depth"></a>max-recursion-depth
</dt>
<dd>
 
 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.
 
 </dd>
<dt>
<a name="max-recursion-queries"></a>max-recursion-queries
</dt>
<dd>
 
 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 domains such as "com" and "net"
 and the DNS root zone are exempt from this limitation.
 The default is 75.
 
 </dd>
<dt>notify-delay</dt>
<dd>
 
 The delay, in seconds, between sending sets of notify
 messages for a zone. The default is five (5) seconds.
 
 
 The overall rate that NOTIFY messages are sent for all
 zones is controlled by serial-query-rate.
 
 </dd>
<dt>max-rsa-exponent-size</dt>
<dd>
 
 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.
 
 </dd>
<dt>prefetch</dt>
<dd>
 
 When a query is received for cached data which
 is to expire shortly, named can
 refresh the data from the authoritative server
 immediately, ensuring that the cache always has an
 answer available.
 
 
 The <code class="option">prefetch</code> specifies the
 "trigger" TTL value at which prefetch of the current
 query will take place: when a cache record with a
 lower TTL value is encountered during query processing,
 it will be refreshed. Valid trigger TTL values are 1 to
 10 seconds. Values larger than 10 seconds will be silently
 reduced to 10.
 Setting a trigger TTL to zero (0) causes
 prefetch to be disabled.
 The default trigger TTL is <code class="literal">2</code>.
 
 
 An optional second argument specifies the "eligibility"
 TTL: the smallest original
 TTL value that will be accepted for a record to be
 eligible for prefetching. The eligibility TTL must
 be at least six seconds longer than the trigger TTL;
 if it isn't, named will silently
 adjust it upward.
 The default eligibility TTL is <code class="literal">9</code>.
 
 </dd>
<dt>v6-bias</dt>
<dd>
 
 When determining the next nameserver to try
 preference IPv6 nameservers by this many milliseconds.
 The default is <code class="literal">50</code> milliseconds.
 
 </dd>
</dl></div>

</div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="builtin"></a>Built-in server information zones</h4></div></div></div>

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
 CHAOS class. These zones are part
 of a
 built-in view (see <a class="xref" href="Bv9ARM.ch06.html#view_statement_grammar" title="view Statement Grammar">the section called &#8220;view Statement Grammar&#8221;</a>) of
 class
 CHAOS which is separate from the
 default view of class IN. Most global
 configuration options (allow-query,
 etc) will apply to this view, but some are locally
 overridden: notify,
 recursion and
 allow-new-zones are
 always set to <code>no</code>, and
 rate-limit is set to allow
 three responses per second.
 
 
 If you need to disable these zones, use the options
 below, or hide the built-in CHAOS
 view by
 defining an explicit view of class CHAOS
 that matches all clients.

<div class="variablelist"><dl class="variablelist">
<dt>version</dt>
<dd>
 
 The version the server should report
 via a query of the name <code class="literal">version.bind</code>
 with type TXT, class CHAOS.
 The default is the real version number of this server.
 Specifying version none
 disables processing of the queries.
 
 </dd>
<dt>hostname</dt>
<dd>
 
 The hostname the server should report via a query of
 the name <code class="filename">hostname.bind</code>
 with type TXT, class CHAOS.
 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 hostname none;
 disables processing of the queries.
 
 </dd>
<dt>server-id</dt>
<dd>
 
 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
 TXT, class CHAOS.
 The primary purpose of such queries is to
 identify which of a group of anycast servers is actually
 answering your queries. Specifying server-id none;
 disables processing of the queries.
 Specifying server-id hostname; will cause named to
 use the hostname as found by the gethostname() function.
 The default server-id is none.
 
 </dd>
</dl></div>

</div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="empty"></a>Built-in Empty Zones</h4></div></div></div>

The named server 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.
 
 
 The server 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.
 
 
 The current list of empty zones is:
 
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">10.IN-ADDR.ARPA</li>
<li class="listitem">16.172.IN-ADDR.ARPA</li>
<li class="listitem">17.172.IN-ADDR.ARPA</li>
<li class="listitem">18.172.IN-ADDR.ARPA</li>
<li class="listitem">19.172.IN-ADDR.ARPA</li>
<li class="listitem">20.172.IN-ADDR.ARPA</li>
<li class="listitem">21.172.IN-ADDR.ARPA</li>
<li class="listitem">22.172.IN-ADDR.ARPA</li>
<li class="listitem">23.172.IN-ADDR.ARPA</li>
<li class="listitem">24.172.IN-ADDR.ARPA</li>
<li class="listitem">25.172.IN-ADDR.ARPA</li>
<li class="listitem">26.172.IN-ADDR.ARPA</li>
<li class="listitem">27.172.IN-ADDR.ARPA</li>
<li class="listitem">28.172.IN-ADDR.ARPA</li>
<li class="listitem">29.172.IN-ADDR.ARPA</li>
<li class="listitem">30.172.IN-ADDR.ARPA</li>
<li class="listitem">31.172.IN-ADDR.ARPA</li>
<li class="listitem">168.192.IN-ADDR.ARPA</li>
<li class="listitem">64.100.IN-ADDR.ARPA</li>
<li class="listitem">65.100.IN-ADDR.ARPA</li>
<li class="listitem">66.100.IN-ADDR.ARPA</li>
<li class="listitem">67.100.IN-ADDR.ARPA</li>
<li class="listitem">68.100.IN-ADDR.ARPA</li>
<li class="listitem">69.100.IN-ADDR.ARPA</li>
<li class="listitem">70.100.IN-ADDR.ARPA</li>
<li class="listitem">71.100.IN-ADDR.ARPA</li>
<li class="listitem">72.100.IN-ADDR.ARPA</li>
<li class="listitem">73.100.IN-ADDR.ARPA</li>
<li class="listitem">74.100.IN-ADDR.ARPA</li>
<li class="listitem">75.100.IN-ADDR.ARPA</li>
<li class="listitem">76.100.IN-ADDR.ARPA</li>
<li class="listitem">77.100.IN-ADDR.ARPA</li>
<li class="listitem">78.100.IN-ADDR.ARPA</li>
<li class="listitem">79.100.IN-ADDR.ARPA</li>
<li class="listitem">80.100.IN-ADDR.ARPA</li>
<li class="listitem">81.100.IN-ADDR.ARPA</li>
<li class="listitem">82.100.IN-ADDR.ARPA</li>
<li class="listitem">83.100.IN-ADDR.ARPA</li>
<li class="listitem">84.100.IN-ADDR.ARPA</li>
<li class="listitem">85.100.IN-ADDR.ARPA</li>
<li class="listitem">86.100.IN-ADDR.ARPA</li>
<li class="listitem">87.100.IN-ADDR.ARPA</li>
<li class="listitem">88.100.IN-ADDR.ARPA</li>
<li class="listitem">89.100.IN-ADDR.ARPA</li>
<li class="listitem">90.100.IN-ADDR.ARPA</li>
<li class="listitem">91.100.IN-ADDR.ARPA</li>
<li class="listitem">92.100.IN-ADDR.ARPA</li>
<li class="listitem">93.100.IN-ADDR.ARPA</li>
<li class="listitem">94.100.IN-ADDR.ARPA</li>
<li class="listitem">95.100.IN-ADDR.ARPA</li>
<li class="listitem">96.100.IN-ADDR.ARPA</li>
<li class="listitem">97.100.IN-ADDR.ARPA</li>
<li class="listitem">98.100.IN-ADDR.ARPA</li>
<li class="listitem">99.100.IN-ADDR.ARPA</li>
<li class="listitem">100.100.IN-ADDR.ARPA</li>
<li class="listitem">101.100.IN-ADDR.ARPA</li>
<li class="listitem">102.100.IN-ADDR.ARPA</li>
<li class="listitem">103.100.IN-ADDR.ARPA</li>
<li class="listitem">104.100.IN-ADDR.ARPA</li>
<li class="listitem">105.100.IN-ADDR.ARPA</li>
<li class="listitem">106.100.IN-ADDR.ARPA</li>
<li class="listitem">107.100.IN-ADDR.ARPA</li>
<li class="listitem">108.100.IN-ADDR.ARPA</li>
<li class="listitem">109.100.IN-ADDR.ARPA</li>
<li class="listitem">110.100.IN-ADDR.ARPA</li>
<li class="listitem">111.100.IN-ADDR.ARPA</li>
<li class="listitem">112.100.IN-ADDR.ARPA</li>
<li class="listitem">113.100.IN-ADDR.ARPA</li>
<li class="listitem">114.100.IN-ADDR.ARPA</li>
<li class="listitem">115.100.IN-ADDR.ARPA</li>
<li class="listitem">116.100.IN-ADDR.ARPA</li>
<li class="listitem">117.100.IN-ADDR.ARPA</li>
<li class="listitem">118.100.IN-ADDR.ARPA</li>
<li class="listitem">119.100.IN-ADDR.ARPA</li>
<li class="listitem">120.100.IN-ADDR.ARPA</li>
<li class="listitem">121.100.IN-ADDR.ARPA</li>
<li class="listitem">122.100.IN-ADDR.ARPA</li>
<li class="listitem">123.100.IN-ADDR.ARPA</li>
<li class="listitem">124.100.IN-ADDR.ARPA</li>
<li class="listitem">125.100.IN-ADDR.ARPA</li>
<li class="listitem">126.100.IN-ADDR.ARPA</li>
<li class="listitem">127.100.IN-ADDR.ARPA</li>
<li class="listitem">0.IN-ADDR.ARPA</li>
<li class="listitem">127.IN-ADDR.ARPA</li>
<li class="listitem">254.169.IN-ADDR.ARPA</li>
<li class="listitem">2.0.192.IN-ADDR.ARPA</li>
<li class="listitem">100.51.198.IN-ADDR.ARPA</li>
<li class="listitem">113.0.203.IN-ADDR.ARPA</li>
<li class="listitem">255.255.255.255.IN-ADDR.ARPA</li>
<li class="listitem">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 class="listitem">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 class="listitem">8.B.D.0.1.0.0.2.IP6.ARPA</li>
<li class="listitem">D.F.IP6.ARPA</li>
<li class="listitem">8.E.F.IP6.ARPA</li>
<li class="listitem">9.E.F.IP6.ARPA</li>
<li class="listitem">A.E.F.IP6.ARPA</li>
<li class="listitem">B.E.F.IP6.ARPA</li>
<li class="listitem">EMPTY.AS112.ARPA</li>
<li class="listitem">HOME.ARPA</li>
</ul></div>

 
 
 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:

<pre class="programlisting">
 disable-empty-zone ".";
</pre>

 
 
 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.
 
 <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 class="variablelist">
<dt>empty-server</dt>
<dd>
 
 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.
 
 </dd>
<dt>empty-contact</dt>
<dd>
 
 Specify what contact name will appear in the returned
 SOA record for empty zones. If none is specified, then
 "." will be used.
 
 </dd>
<dt>empty-zones-enable</dt>
<dd>
 
 Enable or disable all empty zones. By default, they
 are enabled.
 
 </dd>
<dt>disable-empty-zone</dt>
<dd>
 
 Disable individual empty zones. By default, none are
 disabled. This option can be specified multiple times.
 
 </dd>
</dl></div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="acache"></a>Additional Section Caching</h4></div></div></div>

The additional section cache, also called acache,
 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 acache is an internal caching
 mechanism of BIND 9, and is not related to the DNS caching
 server function.

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.

In order to obtain the maximum performance improvement
 from additional section caching, setting
 additional-from-cache
 to no is recommended, since the current
 implementation of acache
 does not short-cut of additional section information from the
 DNS cache data.

One obvious disadvantage of acache 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
 acache mechanism can be
 disabled by setting acache-enable to
 no.
 It is also possible to specify the upper limit of memory
 consumption
 for acache by using max-acache-size.

Additional section caching also has a minor effect on the
 RRset ordering in the additional section.
 Without acache,
 cyclic 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 rrset-order.
 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.

The following is a summary of options related to
 acache.

<div class="variablelist"><dl class="variablelist">
<dt>acache-enable</dt>
<dd>
 
 If yes, additional section caching is
 enabled. The default value is no.
 
 </dd>
<dt>acache-cleaning-interval</dt>
<dd>
 
 The server will remove stale cache entries, based on an LRU
 based
 algorithm, every acache-cleaning-interval minutes.
 The default is 60 minutes.
 If set to 0, no periodic cleaning will occur.
 
 </dd>
<dt>max-acache-size</dt>
<dd>
 
 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>.
 
 </dd>
</dl></div>

</div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="content_filtering"></a>Content Filtering</h4></div></div></div>

<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
 deny-answer-addresses 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
 deny-answer-aliases 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 except-from, 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 deny-answer-aliases
 filter will not apply;
 for example, even if "example.com" is specified for
 deny-answer-aliases,
 
<pre class="programlisting">www.example.com. CNAME xxx.example.com.</pre>

returned by an "example.com" server will be accepted.

In the <code class="varname">address_match_list</code> of the
 deny-answer-addresses 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.

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.

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 class="link" 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.

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:

<pre class="programlisting">deny-answer-addresses { 192.0.2.0/24; } except-from { "example.net"; };
deny-answer-aliases { "example.net"; };
</pre>

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:

<pre class="programlisting">attacker.example.com. A 192.0.2.1</pre>

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.

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

<pre class="programlisting">www.example.net. A 192.0.2.2</pre>

it will be accepted since the owner name "www.example.net"
 matches the except-from element,
 "example.net".

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.

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.
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="rpz"></a>Response Policy Zone (RPZ) Rewriting</h4></div></div></div>

<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.

Response policy zones are named in the
 response-policy option for the view or among the
 global options if there is no response-policy option for the view.
 Response policy zones are ordinary DNS zones containing RRsets
 that can be queried normally if allowed.
 It is usually best to restrict those queries with something like
 allow-query { localhost; };.
 Note that zones using masterfile-format map
 cannot be used as policy zones.

A response-policy option can support
 multiple policy zones. To maximize performance, a radix
 tree is used to quickly identify response policy zones
 containing triggers that match the current query. This
 imposes an upper limit of 32 on the number of policy zones
 in a single response-policy option; more
 than that is a configuration error.

Five policy triggers can be encoded in RPZ records.
 
<div class="variablelist"><dl class="variablelist">
<dt>RPZ-CLIENT-IP</dt>
<dd>
 
 IP records are triggered by the IP address of the
 DNS client.
 Client IP address triggers are encoded in records that have
 owner names that are subdomains of
 rpz-client-ip relativized to the
 policy zone origin name
 and encode an address or address block.
 IPv4 addresses are represented as
 <code>prefixlength.B4.B3.B2.B1.rpz-client-ip</code>.
 The IPv4 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,
 <code>prefixlength.W8.W7.W6.W5.W4.W3.W2.W1.rpz-client-ip</code>.
 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
 IP6.ARPA. (Note that this representation of IPv6
 address is different from IP6.ARPA where each hex
 digit occupies a label.)
 All 8 words must be present except when one set of consecutive
 zero words is replaced with <code>.zz.</code>
 analogous to double colons (::) in standard IPv6 text
 encodings.
 The IPv6 prefix length must be between 1 and 128.
 
 </dd>
<dt>QNAME</dt>
<dd>
 
 QNAME policy records are triggered by query names of
 requests and targets of CNAME records resolved to generate
 the response.
 The owner name of a QNAME policy record is
 the query name relativized to the policy zone.
 
 </dd>
<dt>RPZ-IP</dt>
<dd>
 
 IP triggers are IP addresses in an
 A or AAAA record in the ANSWER section of a response.
 They are encoded like client-IP triggers except as
 subdomains of rpz-ip.
 
 </dd>
<dt>RPZ-NSDNAME</dt>
<dd>
 
 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
 rpz-nsdname 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.
 
 </dd>
<dt>RPZ-NSIP</dt>
<dd>
 
 NSIP triggers match the IP addresses of authoritative
 servers. They are enncoded like IP triggers, except as
 subdomains of rpz-nsip.
 NSDNAME and NSIP triggers are checked only for names with at
 least min-ns-dots dots.
 The default value of min-ns-dots is
 1, to exclude top level domains.
 
 
 If a name server's IP address is not yet known,
 named will recursively look up
 the IP address before applying an RPZ-NSIP rule.
 This can cause a processing delay. To speed up
 processing at the cost of precision, the
 nsip-wait-recurse option
 can be used: when set to <code>no</code>,
 RPZ-NSIP rules will only be applied when a name
 servers's IP address has already been looked up and
 cached. If a server's IP address is not in the
 cache, then the RPZ-NSIP rule will be ignored,
 but the address will be looked up in the
 background, and the rule will be applied
 to subsequent queries. The default is
 <code>yes</code>, meaning RPZ-NSIP
 rules should always be applied even if an
 address needs to be looked up first.
 
 </dd>
</dl></div>

The query response is checked against all response policy zones,
 so two or more policy records can be triggered by a response.
 Because DNS responses are rewritten according to at most one
 policy record, a single record encoding an action (other than
 DISABLED actions) must be chosen.
 Triggers or the records that encode them are chosen for the
 rewriting in the following order:
 
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">Choose the triggered record in the zone that appears
 first in the response-policy option.
 </li>
<li class="listitem">Prefer CLIENT-IP to QNAME to IP to NSDNAME to NSIP
 triggers in a single zone.
 </li>
<li class="listitem">Among NSDNAME triggers, prefer the
 trigger that matches the smallest name under the DNSSEC ordering.
 </li>
<li class="listitem">Among IP or NSIP triggers, prefer the trigger
 with the longest prefix.
 </li>
<li class="listitem">Among triggers with the same prefix length,
 prefer the IP or NSIP trigger that matches
 the smallest IP address.
 </li>
</ol></div>

When the processing of a response is restarted to resolve
 DNAME or CNAME records and a policy record set has
 not been triggered,
 all response policy zones are again consulted for the
 DNAME or CNAME names and addresses.

RPZ record sets are any types of DNS record except
 DNAME or DNSSEC that encode actions or responses to
 individual queries.
 Any of the policies can be used with any of the triggers.
 For example, while the TCP-only policy is
 commonly used with client-IP triggers,
 it can be used with any type of trigger to force the use of
 TCP for responses with owner names in a zone.
 
<div class="variablelist"><dl class="variablelist">
<dt>PASSTHRU</dt>
<dd>
 
 The whitelist policy is specified
 by a CNAME whose target is rpz-passthru.
 It causes the response to not be rewritten
 and is most often used to "poke holes" in policies for
 CIDR blocks.
 
 </dd>
<dt>DROP</dt>
<dd>
 
 The blacklist policy is specified
 by a CNAME whose target is rpz-drop.
 It causes the response to be discarded.
 Nothing is sent to the DNS client.
 
 </dd>
<dt>TCP-Only</dt>
<dd>
 
 The "slip" policy is specified
 by a CNAME whose target is rpz-tcp-only.
 It changes UDP responses to short, truncated DNS responses
 that require the DNS client to try again with TCP.
 It is used to mitigate distributed DNS reflection attacks.
 
 </dd>
<dt>NXDOMAIN</dt>
<dd>
 
 The domain undefined response is encoded
 by a CNAME whose target is the root domain (.)
 
 </dd>
<dt>NODATA</dt>
<dd>
 
 The empty set of resource records is specified by
 CNAME whose target is the wildcard top-level
 domain (*.).
 It rewrites the response to NODATA or ANCOUNT=1.
 
 </dd>
<dt>Local Data</dt>
<dd>
 
 A set of ordinary DNS records can be 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 asterisk (*)
 has been replaced with the query name.
 The purpose for this special form is query logging in the
 walled garden's authority DNS server.
 
 </dd>
</dl></div>

All of the actions specified in all of the individual records
 in a policy zone
 can be overridden with a policy clause in the
 response-policy option.
 An organization using a policy zone provided by another
 organization might use this mechanism to redirect domains
 to its own walled garden.
 
<div class="variablelist"><dl class="variablelist">
<dt>GIVEN</dt>
<dd>
 The placeholder policy says "do not override but
 perform the action specified in the zone."
 
 </dd>
<dt>DISABLED</dt>
<dd>
 
 The testing override policy causes policy zone records to do
 nothing but log what they would have done if the
 policy zone were not disabled.
 The response to the DNS query will be written (or not)
 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.
 
 </dd>
<dt>
PASSTHRU, DROP, TCP-Only, NXDOMAIN, NODATA
</dt>
<dd>
 
 override with the corresponding per-record policy.
 
 </dd>
<dt>CNAME domain</dt>
<dd>
 
 causes all RPZ policy records to act as if they were
 "cname domain" records.
 
 </dd>
</dl></div>

By default, the actions encoded in a response policy zone
 are applied only to queries that ask for recursion (RD=1).
 That default can be changed for a single policy zone or
 all response policy zones in a view
 with a recursive-only no 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.

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 response policy zones in a view with a
 break-dnssec yes 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.

No DNS records are needed for a QNAME or Client-IP trigger.
 The name or IP address itself is sufficient,
 so in principle the query name need not be recursively resolved.
 However, not resolving the requested
 name can leak the fact that response policy rewriting is in use
 and that the name is listed in a policy zone to operators of
 servers for listed names. To prevent that information leak, by
 default any recursion needed for a request is done before any
 policy triggers are considered. Because listed domains often
 have slow authoritative servers, this default behavior can cost
 significant time.
 The qname-wait-recurse no option
 overrides that default behavior when recursion cannot
 change a non-error response.
 The option does not affect QNAME or client-IP triggers
 in policy zones listed
 after other zones containing IP, NSIP and NSDNAME triggers, because
 those may depend on the A, AAAA, and NS records that would be
 found during recursive resolution. It also does not affect
 DNSSEC requests (DO=1) unless break-dnssec yes
 is in use, because the response would depend on whether or not
 RRSIG records were found during resolution.
 Using this option can cause error responses such as SERVFAIL to
 appear to be rewritten, since no recursion is being done to
 discover problems at the authoritative server.

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 max-policy-ttl clause changes the
 maximum seconds from its default of 5.

For example, you might use this option statement
 
<pre class="programlisting"> response-policy { zone "badlist"; };</pre>
 
 and this zone statement
 
<pre class="programlisting"> zone "badlist" {type master; file "master/badlist"; allow-query {none;}; };</pre>
 
 with this zone file
 
<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
*.nxdomain.domain.com   CNAME   .               ; NXDOMAIN policy
nodata.domain.com       CNAME   *.              ; NODATA policy
*.nodata.domain.com     CNAME   *.              ; NODATA policy
bad.domain.com          A       10.0.0.1        ; redirect to a walled garden
                        AAAA    2001:2::1
bzone.domain.com        CNAME   garden.example.com.

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

; 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 responses containing A records in 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   .

; blacklist and whitelist some DNS clients
112.zz.2001.rpz-client-ip    CNAME   rpz-drop.
8.0.0.0.127.rpz-client-ip    CNAME   rpz-drop.

; force some DNS clients and responses in the example.com zone to TCP
16.0.0.1.10.rpz-client-ip   CNAME   rpz-tcp-only.
example.com                 CNAME   rpz-tcp-only.
*.example.com               CNAME   rpz-tcp-only.

</pre>
 
 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.

Responses rewritten by RPZ are counted in the
 RPZRewrites statistics.

The log clause can be used to optionally
 turn off rewrite logging for a particular response policy
 zone. By default, all rewrites are logged.
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="rrl"></a>Response Rate Limiting</h4></div></div></div>

Excessive almost identical UDP responses
 can be controlled by configuring a
 rate-limit clause in an
 options or view 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.

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.

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 window 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 window
 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.

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 ipv4-prefix-length (default 24)
 and ipv6-prefix-length (default 56).

All non-empty responses for a valid domain name (qname)
 and record type (qtype) are identical and have a limit specified
 with responses-per-second
 (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
 nodata-per-second
 (default responses-per-second).
 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 nxdomains-per-second
 (default responses-per-second).
 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
 referrals-per-second
 (default responses-per-second).

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.

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
 responses-per-second value,
 but it can be set separately with
 errors-per-second.

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 slip 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.
 slip 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 slip rate.

(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
 slip to 1, causing all rate-limited
 responses to be truncated rather than dropped. This reduces
 the effectiveness of rate-limiting against reflection attacks.)

When the approximate query per second rate exceeds
 the qps-scale value,
 then the responses-per-second,
 errors-per-second,
 nxdomains-per-second and
 all-per-second values are reduced by the
 ratio of the current rate to the qps-scale value.
 This feature can tighten defenses during attacks.
 For example, with
 qps-scale 250; responses-per-second 20; 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.

Rate limiters for different name spaces maintain
 separate counters: If, for example, there is a
 rate-limit statement for "com" and
 another for "example.com", queries matching "example.com"
 will not be debited against the rate limiter for "com".

If a rate-limit statement does not specify a
 domain, then it applies to the root domain
 (".") and thus affects the entire DNS namespace, except those
 portions covered by other rate-limit
 statements.

Communities of DNS clients can be given their own parameters or no
 rate limiting by putting
 rate-limit statements in view
 statements instead of the global option
 statement.
 A rate-limit statement in a view replaces,
 rather than supplementing, a rate-limit
 statement among the main options.
 DNS clients within a view can be exempted from rate limits
 with the exempt-clients clause.

UDP responses of all kinds can be limited with the
 all-per-second phrase. This rate
 limiting is unlike the rate limiting provided by
 responses-per-second,
 errors-per-second, and
 nxdomains-per-second 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 all-per-second limit
 are always dropped; the slip value
 has no effect. An all-per-second
 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 Mail From
 command. Web browsers often repeatedly resolve the
 same names that are repeated in HTML &lt;IMG&gt; tags
 in a page. all-per-second 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 make TCP connections
 or parsing DNS requests, but that rate limiting must
 be done before the DNS server sees the requests.

The maximum size of the table used to track requests and
 rate limit responses is set with max-table-size.
 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,
 min-table-size (default 500)
 can set the minimum table size.
 Enable rate-limit category logging to monitor
 expansions of the table and inform
 choices for the initial and maximum table size.

Use log-only yes to test rate limiting parameters
 without actually dropping any requests.

Responses dropped by rate limits are included in the
 RateDropped and QryDropped
 statistics.
 Responses that truncated by rate limits are included in
 RateSlipped and RespTruncated.
 
 </div>

<div class="section">
<div class="titlepage"></div>
 
 Named supports NXDOMAIN redirection via two methods:
 
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">Redirect zone <a class="xref" href="Bv9ARM.ch06.html#zone_statement_grammar" title="zone Statement Grammar">the section called &#8220;zone
 Statement Grammar&#8221;</a>
</li>
<li class="listitem">Redirect namespace</li>
</ul></div>

 
 
 With both methods when named gets a NXDOMAIN response
 it examines a separate namespace to see if the NXDOMAIN
 response should be replaced with an alternative response.
 
 
 With a redirect zone (zone "." { type redirect; };), the
 data used to replace the NXDOMAIN is held in a single
 zone which is not part of the normal namespace. All the
 redirect information is contained in the zone; there are
 no delegations.
 
 
 With a redirect namespace (option { nxdomain-redirect
 &lt;suffix&gt; };) the data used to replace the
 NXDOMAIN is part of the normal namespace and is looked up by
 appending the specified suffix to the original query name.
 This roughly doubles the cache required to process NXDOMAIN
 responses as you have the original NXDOMAIN response and
 the replacement data or a NXDOMAIN indicating that there
 is no replacement.
 
 
 If both a redirect zone and a redirect namespace are configured,
 the redirect zone is tried first.
 
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="server_statement_grammar"></a>server Statement Grammar</h3></div></div></div>
 <pre class="programlisting">
server <code>netprefix</code> {
	bogus <code>boolean</code>;
	edns <code>boolean</code>;
	edns-udp-size <code>integer</code>;
	edns-version <code>integer</code>;
	keys <code>server_key</code>;
	max-udp-size <code>integer</code>;
	notify-source ( <code>ipv4_address</code> | * ) [ port ( <code>integer</code> | * ) ] [
	 dscp <code>integer</code> ];
	notify-source-v6 ( <code>ipv6_address</code> | * ) [ port ( <code>integer</code> | * ) ]
	 [ dscp <code>integer</code> ];
	provide-ixfr <code>boolean</code>;
	query-source ( ( [ address ] ( <code>ipv4_address</code> | * ) [ port (
	 <code>integer</code> | * ) ] ) | ( [ [ address ] ( <code>ipv4_address</code> | * ) ]
	 port ( <code>integer</code> | * ) ) ) [ dscp <code>integer</code> ];
	query-source-v6 ( ( [ address ] ( <code>ipv6_address</code> | * ) [ port (
	 <code>integer</code> | * ) ] ) | ( [ [ address ] ( <code>ipv6_address</code> | * ) ]
	 port ( <code>integer</code> | * ) ) ) [ dscp <code>integer</code> ];
	request-expire <code>boolean</code>;
	request-ixfr <code>boolean</code>;
	request-nsid <code>boolean</code>;
	send-cookie <code>boolean</code>;
	tcp-only <code>boolean</code>;
	transfer-format ( many-answers | one-answer );
	transfer-source ( <code>ipv4_address</code> | * ) [ port ( <code>integer</code> | * ) ] [
	 dscp <code>integer</code> ];
	transfer-source-v6 ( <code>ipv6_address</code> | * ) [ port ( <code>integer</code> | * )
	 ] [ dscp <code>integer</code> ];
	transfers <code>integer</code>;
};
</pre>
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="server_statement_definition_and_usage"></a>server Statement Definition and
 Usage</h3></div></div></div>

The server 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>.

The server statement can occur at
 the top level of the
 configuration file or inside a view
 statement.
 If a view statement contains
 one or more server statements, only
 those
 apply to the view and any top-level ones are ignored.
 If a view contains no server
 statements,
 any top-level server statements are
 used as
 defaults.

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 bogus is no.
 
 
 The provide-ixfr 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 yes, incremental transfer
 will be provided
 whenever possible. If set to no,
 all transfers
 to the remote server will be non-incremental. If not set, the
 value
 of the provide-ixfr option in the
 view or
 global options block is used as a default.

The request-ixfr 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 request-ixfr 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.

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 yes should always work.
 The purpose of the provide-ixfr and
 request-ixfr 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.

The request-expire clause determines
 whether the local server, when acting as a slave, will
 request the EDNS EXPIRE value. The EDNS EXPIRE value
 indicates the remaining time before the zone data will
 expire and need to be be refreshed. This is used
 when a secondary server transfers a zone from another
 secondary server; when transferring from the primary, the
 expiration timer is set from the EXPIRE field of the SOA
 record instead.
 The default is yes.

The edns clause determines whether
 the local server will attempt to use EDNS when communicating
 with the remote server. The default is yes.

The edns-udp-size option sets the
 EDNS UDP size that is advertised by named
 when querying the remote server. Valid values are 512
 to 4096 bytes (values outside this range will be silently
 adjusted to the nearest value within it). This option
 is useful when you wish to advertise 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. (Note: Currently,
 this sets a single UDP size for all packets sent to the
 server; named will not deviate from
 this value. This differs from the behavior of
 edns-udp-size in options
 or view statements, where it specifies
 a maximum value. The server statement
 behavior may be brought into conformance with the
 options/view behavior in future releases.)

The edns-version option sets the
 maximum EDNS VERSION that will be sent to the server(s)
 by the resolver. The actual EDNS version sent is still
 subject to normal EDNS version negotiation rules (see
 RFC 6891), the maximum EDNS version supported by the
 server, and any other heuristics that indicate that a
 lower version should be sent. This option is intended
 to be used when a remote server reacts badly to a given
 EDNS version or higher; it should be set to the highest
 version the remote server is known to support. Valid
 values are 0 to 255; higher values will be silently
 adjusted. This option will not be needed until higher
 EDNS versions than 0 are in use.

The max-udp-size option sets the
 maximum EDNS UDP message size named
 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 named.

The tcp-only option sets the transport
 protocol to TCP. The default is to use the UDP transport
 and to fallback on TCP only when a truncated response
 is received.

The server supports two zone transfer methods. The first, one-answer,
 uses one DNS message per resource record transferred. many-answers packs
 as many resource records as possible into a message. many-answers 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 transfer-format option.
 If transfer-format is not
 specified, the transfer-format
 specified
 by the options statement will be
 used.

transfers
 is used to limit the number of concurrent inbound zone
 transfers from the specified server. If no
 transfers clause is specified, the
 limit is set according to the
 transfers-per-ns option.

The keys clause identifies a
 key_id defined by the key statement,
 to be used for transaction security (TSIG, <a class="xref" 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.

Only a single key per server is currently supported.

The transfer-source and
 transfer-source-v6 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 transfer-source can
 be specified.
 Similarly, for an IPv6 remote server, only
 transfer-source-v6 can be
 specified.
 For more details, see the description of
 transfer-source and
 transfer-source-v6 in
 <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.

The notify-source and
 notify-source-v6 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 notify-source
 can be specified. Similarly, for an IPv6 remote server,
 only notify-source-v6 can be specified.

The query-source and
 query-source-v6 clauses specify the
 IPv4 and IPv6 source address to be used for queries
 sent to remote servers, respectively. For an IPv4
 remote server, only query-source can
 be specified. Similarly, for an IPv6 remote server,
 only query-source-v6 can be specified.

The request-nsid clause determines
 whether the local server will add a NSID EDNS option
 to requests sent to the server. This overrides
 request-nsid set at the view or
 option level.

The send-cookie clause determines
 whether the local server will add a COOKIE EDNS option
 to requests sent to the server. This overrides
 send-cookie set at the view or
 option level. The named server may
 determine that COOKIE is not supported by the remote server
 and not add a COOKIE EDNS option to requests.
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="statschannels"></a>statistics-channels Statement Grammar</h3></div></div></div>
 <pre class="programlisting">
statistics-channels {
	inet ( <code>ipv4_address</code> | <code>ipv6_address</code> |
	 * ) [ port ( <code>integer</code> | * ) ] [
	 allow { <code>address_match_element</code>; ...
	 } ];
};
</pre>
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="statistics_channels"></a>statistics-channels Statement Definition and
 Usage</h3></div></div></div>

The statistics-channels statement
 declares communication channels to be used by system
 administrators to get access to statistics information of
 the name server.

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 and/or
 json-c (also known as libjson0); the
 statistics-channels statement is
 still accepted even if it is built without the library,
 but any HTTP access will fail with an error.

An inet control channel is a TCP socket
 listening at the specified ip_port on the
 specified ip_addr, which can be an IPv4 or IPv6
 address. An ip_addr 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 ip_addr of <code class="literal">::</code>.

If no port is specified, port 80 is used for HTTP channels.
 The asterisk "<code class="literal">*</code>" cannot be used for
 ip_port.

The attempt of opening a statistics channel is
 restricted by the optional allow clause.
 Connections to the statistics channel are permitted based on the
 address_match_list.
 If no allow clause is present,
 named 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.

If no statistics-channels statement is present,
 named will not open any communication channels.

The statistics are available in various formats and views
 depending on the URI used to access them. For example, 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 class="link" href="http://127.0.0.1:8888/" target="_top">http://127.0.0.1:8888/</a> or
 <a class="link" 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, and into
 charts and graphs using the Google Charts API when using a
 javascript-capable browser.

Applications that depend on a particular XML schema
 can request
 <a class="link" 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 class="link" 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.

Broken-out subsets of the statistics can be viewed at
 <a class="link" href="http://127.0.0.1:8888/xml/v3/status" target="_top">http://127.0.0.1:8888/xml/v3/status</a>
 (server uptime and last reconfiguration time),
 <a class="link" href="http://127.0.0.1:8888/xml/v3/server" target="_top">http://127.0.0.1:8888/xml/v3/server</a>
 (server and resolver statistics),
 <a class="link" href="http://127.0.0.1:8888/xml/v3/zones" target="_top">http://127.0.0.1:8888/xml/v3/zones</a>
 (zone statistics),
 <a class="link" href="http://127.0.0.1:8888/xml/v3/net" target="_top">http://127.0.0.1:8888/xml/v3/net</a>
 (network status and socket statistics),
 <a class="link" href="http://127.0.0.1:8888/xml/v3/mem" target="_top">http://127.0.0.1:8888/xml/v3/mem</a>
 (memory manager statistics),
 <a class="link" href="http://127.0.0.1:8888/xml/v3/tasks" target="_top">http://127.0.0.1:8888/xml/v3/tasks</a>
 (task manager statistics), and
 <a class="link" href="http://127.0.0.1:8888/xml/v3/traffic" target="_top">http://127.0.0.1:8888/xml/v3/traffic</a>
 (traffic sizes).

The full set of statistics can also be read in JSON format at
 <a class="link" href="http://127.0.0.1:8888/json" target="_top">http://127.0.0.1:8888/json</a>,
 with the broken-out subsets at
 <a class="link" href="http://127.0.0.1:8888/json/v1/status" target="_top">http://127.0.0.1:8888/json/v1/status</a>
 (server uptime and last reconfiguration time),
 <a class="link" href="http://127.0.0.1:8888/json/v1/server" target="_top">http://127.0.0.1:8888/json/v1/server</a>
 (server and resolver statistics),
 <a class="link" href="http://127.0.0.1:8888/json/v1/zones" target="_top">http://127.0.0.1:8888/json/v1/zones</a>
 (zone statistics),
 <a class="link" href="http://127.0.0.1:8888/json/v1/net" target="_top">http://127.0.0.1:8888/json/v1/net</a>
 (network status and socket statistics),
 <a class="link" href="http://127.0.0.1:8888/json/v1/mem" target="_top">http://127.0.0.1:8888/json/v1/mem</a>
 (memory manager statistics),
 <a class="link" href="http://127.0.0.1:8888/json/v1/tasks" target="_top">http://127.0.0.1:8888/json/v1/tasks</a>
 (task manager statistics), and
 <a class="link" href="http://127.0.0.1:8888/json/v1/traffic" target="_top">http://127.0.0.1:8888/json/v1/traffic</a>
 (traffic sizes).
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="trusted-keys"></a>trusted-keys Statement Grammar</h3></div></div></div>
 <pre class="programlisting">
trusted-keys { <code>string</code> <code>integer</code> <code>integer</code>
 <code>integer</code> <code>quoted_string</code>; ... };
</pre>
 </div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="trusted_keys"></a>trusted-keys Statement Definition
 and Usage</h3></div></div></div>

The trusted-keys statement defines
 DNSSEC security roots. DNSSEC is described in <a class="xref" 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.
 
 
 All keys (and corresponding zones) listed in
 trusted-keys are deemed to exist regardless
 of what parent zones say. Similarly for all keys listed in
 trusted-keys only those keys are
 used to validate the DNSKEY RRset. The parent's DS RRset
 will not be used.
 
 
 The trusted-keys statement can contain
 multiple key entries, each consisting of the key's
 domain name, flags, protocol, algorithm, and the Base64
 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.
 
 
 trusted-keys 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.
 
 
 Validation below specified names can be temporarily disabled
 by using rndc nta.
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="managed_keys"></a>managed-keys Statement Grammar</h3></div></div></div>
 <pre class="programlisting">
managed-keys { <code>string</code> <code>string</code> <code>integer</code>
 <code>integer</code> <code>integer</code> <code>quoted_string</code>; ... };
</pre>
 </div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="managed-keys"></a>managed-keys Statement Definition
 and Usage</h3></div></div></div>

The managed-keys statement, like
 trusted-keys, defines DNSSEC
 security roots. The difference is that
 managed-keys can be kept up to date
 automatically, without intervention from the resolver
 operator.
 
 
 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
 trusted-keys 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
 trusted-keys statement with the new key.
 
 
 If, however, the zone were listed in a
 managed-keys statement instead, then the
 zone owner could add a "stand-by" key to the zone in advance.
 named would store the stand-by key, and
 when the original key was revoked, named
 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.
 
 
 A managed-keys 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 is
 <code class="literal">initial-key</code>.
 This means the managed-keys statement must
 contain a copy of the initializing key. (Future releases may
 allow keys to be initialized by other methods, eliminating this
 requirement.)
 
 
 Consequently, a managed-keys statement
 appears similar to a trusted-keys, 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 trusted-keys continue to be
 trusted until they are removed from
 <code class="filename">named.conf</code>, an initializing key listed
 in a managed-keys statement is only trusted
 once: for as long as it takes to load the
 managed key database and start the RFC 5011 key maintenance
 process.
 
 
 The first time named 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 managed-keys
 statement. If the DNSKEY RRset is validly signed, then it is
 used as the basis for a new managed keys database.
 
 
 From that point on, whenever named runs, it
 sees the managed-keys 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 managed-keys
 statement is not used to validate answers; it has been
 superseded by the key or keys stored in the managed keys database.
 
 
 The next time named runs after a name
 has been removed from the
 managed-keys 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.
 
 
 In the current implementation, the managed keys database
 is stored as a master-format zone file.
 
 
 On servers which do not use views, this file is named
 <code class="filename">managed-keys.bind</code>. When views are in
 use, there will be a separate managed keys database for each
 view; the filename will be the view name (or, if a view name
 contains characters which would make it illegal as a filename,
 a hash of the view name), followed by
 the suffix <code class="filename">.mkeys</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, e.g.,
 <code class="filename">managed-keys.bind.jnl</code> or
 <code class="filename">internal.mkeys.jnl</code>.
 Changes are committed to the master file as soon as
 possible afterward; this will usually occur within 30
 seconds. So, whenever named is using
 automatic key maintenance, the zone file and journal file
 can be expected to exist in the working directory.
 (For this reason among others, the working directory
 should be always be writable by named.)
 
 
 If the dnssec-validation option is
 set to <code>auto</code>, named
 will automatically initialize a managed key for the
 root zone. The key that is used to initialize the key
 maintenance process is stored in <code class="filename">bind.keys</code>;
 the location of this file can be overridden with the
 bindkeys-file option. As a fallback
 in the event no <code class="filename">bind.keys</code> can be
 found, the initializing key is also compiled directly
 into named.
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="view_statement_grammar"></a>view Statement Grammar</h3></div></div></div>

<pre class="programlisting">view <code>view_name</code> [ <code>class</code> ] {
 match-clients { <code>address_match_list</code> } ;
 match-destinations { <code>address_match_list</code> } ;
 match-recursive-only <code>yes_or_no</code> ;
 [ <code>view_option</code> ; ... ]
 [ <code>zone_statement</code> ; ... ]
} ;
</pre>

</div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="view_statement"></a>view Statement Definition and Usage</h3></div></div></div>

The view 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.

Each view 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
 match-clients clause and its
 destination IP address matches
 the <code class="varname">address_match_list</code> of the
 view's
 match-destinations clause. If not
 specified, both
 match-clients and match-destinations
 default to matching all addresses. In addition to checking IP
 addresses
 match-clients and match-destinations
 can also take keys which provide an
 mechanism for the
 client to select the view. A view can also be specified
 as match-recursive-only, which
 means that only recursive
 requests from matching clients will match that view.
 The order of the view statements is
 significant &#8212;
 a client request will be resolved in the context of the first
 view that it matches.

Zones defined within a view
 statement will
 only be accessible to clients that match the view.
 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.

Many of the options given in the options statement
 can also be used within a view
 statement, and then
 apply only when resolving queries with that view. When no
 view-specific
 value is given, the value in the options statement
 is used as a default. Also, zone options can have default values
 specified
 in the view statement; these
 view-specific defaults
 take precedence over those in the options statement.

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.

If there are no view statements in
 the config
 file, a default view that matches any client is automatically
 created
 in class IN. Any zone statements
 specified on
 the top level of the configuration file are considered to be part
 of
 this default view, and the options
 statement will
 apply to the default view. If any explicit view
 statements are present, all zone
 statements must
 occur inside view statements.

Here is an example of a typical split DNS setup implemented
 using view statements:

<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="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="zone_statement_grammar"></a>zone
 Statement Grammar</h3></div></div></div>

<pre class="programlisting">
zone <code>string</code> [ <code>class</code> ] {
	type ( master | primary );
	allow-query { <code>address_match_element</code>; ... };
	allow-query-on { <code>address_match_element</code>; ... };
	allow-transfer { <code>address_match_element</code>; ... };
	allow-update { <code>address_match_element</code>; ... };
	also-notify [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>masters</code> | <code>ipv4_address</code> [ port <code>integer</code> ] | <code>ipv6_address</code> [ port <code>integer</code> ] ) [ key <code>string</code> ]; ... };
	alt-transfer-source ( <code>ipv4_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	alt-transfer-source-v6 ( <code>ipv6_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	auto-dnssec ( allow | maintain | off );
	check-dup-records ( fail | warn | ignore );
	check-integrity <code>boolean</code>;
	check-mx ( fail | warn | ignore );
	check-mx-cname ( fail | warn | ignore );
	check-names ( fail | warn | ignore );
	check-sibling <code>boolean</code>;
	check-spf ( warn | ignore );
	check-srv-cname ( fail | warn | ignore );
	check-wildcard <code>boolean</code>;
	database <code>string</code>;
	dialup ( notify | notify-passive | passive | refresh | <code>boolean</code> );
	dlz <code>string</code>;
	dnssec-dnskey-kskonly <code>boolean</code>;
	dnssec-loadkeys-interval <code>integer</code>;
	dnssec-secure-to-insecure <code>boolean</code>;
	dnssec-update-mode ( maintain | no-resign );
	file <code>quoted_string</code>;
	forward ( first | only );
	forwarders [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>ipv4_address</code> | <code>ipv6_address</code> ) [ port <code>integer</code> ] [ dscp <code>integer</code> ]; ... };
	inline-signing <code>boolean</code>;
	ixfr-from-differences <code>boolean</code>;
	journal <code>quoted_string</code>;
	key-directory <code>quoted_string</code>;
	masterfile-format ( map | raw | text );
	masterfile-style ( full | relative );
	max-journal-size ( unlimited | <code>sizeval</code> );
	max-records <code>integer</code>;
	max-transfer-idle-out <code>integer</code>;
	max-transfer-time-out <code>integer</code>;
	max-zone-ttl ( unlimited | <code>ttlval</code> );
	notify ( explicit | master-only | <code>boolean</code> );
	notify-delay <code>integer</code>;
	notify-source ( <code>ipv4_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	notify-source-v6 ( <code>ipv6_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	notify-to-soa <code>boolean</code>;
	serial-update-method ( date | increment | unixtime );
	sig-signing-nodes <code>integer</code>;
	sig-signing-signatures <code>integer</code>;
	sig-signing-type <code>integer</code>;
	sig-validity-interval <code>integer</code> [ <code>integer</code> ];
	update-check-ksk <code>boolean</code>;
	update-policy ( local | { ( deny | grant ) <code>string</code> ( 6to4-self | external | krb5-self | krb5-subdomain | ms-self | ms-subdomain | name | self | selfsub | selfwild | subdomain | tcp-self | wildcard | zonesub ) [ <code>string</code> ] <code>rrtypelist</code>; ... };
	zero-no-soa-ttl <code>boolean</code>;
	zone-statistics ( full | terse | none | <code>boolean</code> );
};
</pre>
<pre class="programlisting">
zone <code>string</code> [ <code>class</code> ] {
	type ( slave | secondary );
	allow-notify { <code>address_match_element</code>; ... };
	allow-query { <code>address_match_element</code>; ... };
	allow-query-on { <code>address_match_element</code>; ... };
	allow-transfer { <code>address_match_element</code>; ... };
	allow-update-forwarding { <code>address_match_element</code>; ... };
	also-notify [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>masters</code> | <code>ipv4_address</code> [ port <code>integer</code> ] | <code>ipv6_address</code> [ port <code>integer</code> ] ) [ key <code>string</code> ]; ... };
	alt-transfer-source ( <code>ipv4_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	alt-transfer-source-v6 ( <code>ipv6_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	auto-dnssec ( allow | maintain | off );
	check-names ( fail | warn | ignore );
	database <code>string</code>;
	dialup ( notify | notify-passive | passive | refresh | <code>boolean</code> );
	dlz <code>string</code>;
	dnssec-dnskey-kskonly <code>boolean</code>;
	dnssec-loadkeys-interval <code>integer</code>;
	dnssec-update-mode ( maintain | no-resign );
	file <code>quoted_string</code>;
	forward ( first | only );
	forwarders [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>ipv4_address</code> | <code>ipv6_address</code> ) [ port <code>integer</code> ] [ dscp <code>integer</code> ]; ... };
	inline-signing <code>boolean</code>;
	ixfr-from-differences <code>boolean</code>;
	journal <code>quoted_string</code>;
	key-directory <code>quoted_string</code>;
	masterfile-format ( map | raw | text );
	masterfile-style ( full | relative );
	masters [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>masters</code> | <code>ipv4_address</code> [ port <code>integer</code> ] | <code>ipv6_address</code> [ port <code>integer</code> ] ) [ key <code>string</code> ]; ... };
	max-journal-size ( unlimited | <code>sizeval</code> );
	max-records <code>integer</code>;
	max-refresh-time <code>integer</code>;
	max-retry-time <code>integer</code>;
	max-transfer-idle-in <code>integer</code>;
	max-transfer-idle-out <code>integer</code>;
	max-transfer-time-in <code>integer</code>;
	max-transfer-time-out <code>integer</code>;
	min-refresh-time <code>integer</code>;
	min-retry-time <code>integer</code>;
	multi-master <code>boolean</code>;
	notify ( explicit | master-only | <code>boolean</code> );
	notify-delay <code>integer</code>;
	notify-source ( <code>ipv4_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	notify-source-v6 ( <code>ipv6_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	notify-to-soa <code>boolean</code>;
	request-expire <code>boolean</code>;
	request-ixfr <code>boolean</code>;
	sig-signing-nodes <code>integer</code>;
	sig-signing-signatures <code>integer</code>;
	sig-signing-type <code>integer</code>;
	sig-validity-interval <code>integer</code> [ <code>integer</code> ];
	transfer-source ( <code>ipv4_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	transfer-source-v6 ( <code>ipv6_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	try-tcp-refresh <code>boolean</code>;
	update-check-ksk <code>boolean</code>;
	use-alt-transfer-source <code>boolean</code>;
	zero-no-soa-ttl <code>boolean</code>;
	zone-statistics ( full | terse | none | <code>boolean</code> );
};
</pre>
<pre class="programlisting">
zone <code>string</code> [ <code>class</code> ] {
	type hint;
	check-names ( fail | warn | ignore );
	delegation-only <code>boolean</code>;
	file <code>quoted_string</code>;
};
</pre>
<pre class="programlisting">
zone <code>string</code> [ <code>class</code> ] {
	type stub;
	allow-query { <code>address_match_element</code>; ... };
	allow-query-on { <code>address_match_element</code>; ... };
	check-names ( fail | warn | ignore );
	database <code>string</code>;
	delegation-only <code>boolean</code>;
	dialup ( notify | notify-passive | passive | refresh | <code>boolean</code> );
	file <code>quoted_string</code>;
	forward ( first | only );
	forwarders [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>ipv4_address</code> | <code>ipv6_address</code> ) [ port <code>integer</code> ] [ dscp <code>integer</code> ]; ... };
	masterfile-format ( map | raw | text );
	masterfile-style ( full | relative );
	masters [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>masters</code> | <code>ipv4_address</code> [ port <code>integer</code> ] | <code>ipv6_address</code> [ port <code>integer</code> ] ) [ key <code>string</code> ]; ... };
	max-records <code>integer</code>;
	max-refresh-time <code>integer</code>;
	max-retry-time <code>integer</code>;
	max-transfer-idle-in <code>integer</code>;
	max-transfer-time-in <code>integer</code>;
	min-refresh-time <code>integer</code>;
	min-retry-time <code>integer</code>;
	multi-master <code>boolean</code>;
	transfer-source ( <code>ipv4_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	transfer-source-v6 ( <code>ipv6_address</code> | * ) [ port ( <code>integer</code> | * ) ] [ dscp <code>integer</code> ];
	use-alt-transfer-source <code>boolean</code>;
	zone-statistics ( full | terse | none | <code>boolean</code> );
};
</pre>
<pre class="programlisting">
zone <code>string</code> [ <code>class</code> ] {
	type static-stub;
	allow-query { <code>address_match_element</code>; ... };
	allow-query-on { <code>address_match_element</code>; ... };
	forward ( first | only );
	forwarders [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>ipv4_address</code> | <code>ipv6_address</code> ) [ port <code>integer</code> ] [ dscp <code>integer</code> ]; ... };
	max-records <code>integer</code>;
	server-addresses { ( <code>ipv4_address</code> | <code>ipv6_address</code> ) [ port <code>integer</code> ]; ... };
	server-names { <code>quoted_string</code>; ... };
	zone-statistics ( full | terse | none | <code>boolean</code> );
};
</pre>
<pre class="programlisting">
zone <code>string</code> [ <code>class</code> ] {
	type forward;
	delegation-only <code>boolean</code>;
	forward ( first | only );
	forwarders [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>ipv4_address</code> | <code>ipv6_address</code> ) [ port <code>integer</code> ] [ dscp <code>integer</code> ]; ... };
};
</pre>
<pre class="programlisting">
zone <code>string</code> [ <code>class</code> ] {
	type redirect;
	allow-query { <code>address_match_element</code>; ... };
	allow-query-on { <code>address_match_element</code>; ... };
	dlz <code>string</code>;
	file <code>quoted_string</code>;
	masterfile-format ( map | raw | text );
	masterfile-style ( full | relative );
	masters [ port <code>integer</code> ] [ dscp <code>integer</code> ] { ( <code>masters</code> | <code>ipv4_address</code> [ port <code>integer</code> ] | <code>ipv6_address</code> [ port <code>integer</code> ] ) [ key <code>string</code> ]; ... };
	max-records <code>integer</code>;
	max-zone-ttl ( unlimited | <code>ttlval</code> );
	zone-statistics ( full | terse | none | <code>boolean</code> );
};
</pre>
<pre class="programlisting">
zone <code>string</code> [ <code>class</code> ] {
	type delegation-only;
};
</pre>
<pre class="programlisting">
zone <code>string</code> [ <code>class</code> ] {
	in-view <code>string</code>;
};
</pre>

</div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="zone_statement"></a>zone Statement Definition and Usage</h3></div></div></div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="zone_types"></a>Zone Types</h4></div></div></div>
 
 The type keyword is required
 for the zone configuration unless
 it is an in-view configuration. Its
 acceptable values include: <code class="varname">delegation-only</code>,
 <code class="varname">forward</code>, <code class="varname">hint</code>,
 <code class="varname">master</code>, <code class="varname">redirect</code>,
 <code class="varname">slave</code>, <code class="varname">static-stub</code>,
 and <code class="varname">stub</code>.

<div class="informaltable">
 <table border="1">
<colgroup>
<col class="1">
<col width="4.017in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 
 <code class="varname">master</code>
 
 </td>
<td>
 
 The server has a master copy of the data
 for the zone and will be able to provide authoritative
 answers for
 it.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">slave</code>
 
 </td>
<td>
 
 A slave zone is a replica of a master
 zone. The masters 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.)
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">stub</code>
 
 </td>
<td>
 
 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.

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.

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.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">static-stub</code>
 
 </td>
<td>
 
 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.
 
 
 Zone data is configured via the
 server-addresses and
 server-names zone options.
 
 
 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 rndc dumpdb -all.
 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.
 
 
 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.
 
 
 Each static-stub zone is configured with
 internally generated NS and (if necessary)
 glue A or AAAA RRs
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">forward</code>
 
 </td>
<td>
 
 A "forward zone" is a way to configure
 forwarding on a per-domain basis. A zone statement
 of type forward can
 contain a forward
 and/or forwarders
 statement,
 which will apply to queries within the domain given by
 the zone
 name. If no forwarders
 statement is present or
 an empty list for forwarders is given, then no
 forwarding will be done for the domain, canceling the
 effects of
 any forwarders in the options statement. Thus
 if you want to use this type of zone to change the
 behavior of the
 global forward 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.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">hint</code>
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">redirect</code>
 
 </td>
<td>
 
 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. allow-query can be
 used to restrict which clients see these answers.
 
 
 If the client has requested DNSSEC records (DO=1) and
 the NXDOMAIN response is signed then no substitution
 will occur.
 
 
 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>.
 
 
 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.".
 
 
 Note that the redirect zone supports all
 possible types; it is not limited to A and
 AAAA records.
 
 
 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
 rndc reload
 <code>zonename</code>
 to reload a redirect zone. However, when using
 rndc reload without specifying
 a zone name, redirect zones will be reloaded along
 with other zones.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">delegation-only</code>
 
 </td>
<td>
 
 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.
 
 
 <code class="varname">delegation-only</code> has no
 effect on answers received from forwarders.
 
 
 See caveats in <a class="xref" href="Bv9ARM.ch06.html#root_delegation_only">root-delegation-only</a>.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="class"></a>Class</h4></div></div></div>

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.
 
 
 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.
 
 
 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.
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="zone_options"></a>Zone Options</h4></div></div></div>

<div class="variablelist"><dl class="variablelist">
<dt>allow-notify</dt>
<dd>
 
 See the description of
 allow-notify in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
 
 </dd>
<dt>allow-query</dt>
<dd>
 
 See the description of
 allow-query in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
 
 </dd>
<dt>allow-query-on</dt>
<dd>
 
 See the description of
 allow-query-on in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
 
 </dd>
<dt>allow-transfer</dt>
<dd>
 
 See the description of allow-transfer
 in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
 
 </dd>
<dt>allow-update</dt>
<dd>
 
 See the description of allow-update
 in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
 
 </dd>
<dt>update-policy</dt>
<dd>
 
 Specifies a "Simple Secure Update" policy. See
 <a class="xref" href="Bv9ARM.ch06.html#dynamic_update_policies" title="Dynamic Update Policies">the section called &#8220;Dynamic Update Policies&#8221;</a>.
 
 </dd>
<dt>allow-update-forwarding</dt>
<dd>
 
 See the description of allow-update-forwarding
 in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called &#8220;Access Control&#8221;</a>.
 
 </dd>
<dt>also-notify</dt>
<dd>
 
 Only meaningful if notify
 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 also-notify. A port
 may be specified
 with each also-notify
 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.
 also-notify is not
 meaningful for stub zones.
 The default is the empty list.
 
 </dd>
<dt>check-names</dt>
<dd>
 
 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 master zones the default is fail. For slave
 zones the default is warn.
 It is not implemented for hint zones.
 
 </dd>
<dt>check-mx</dt>
<dd>
 
 See the description of
 check-mx in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>check-spf</dt>
<dd>
 
 See the description of
 check-spf in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>check-wildcard</dt>
<dd>
 
 See the description of
 check-wildcard in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>check-integrity</dt>
<dd>
 
 See the description of
 check-integrity in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>check-sibling</dt>
<dd>
 
 See the description of
 check-sibling in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>zero-no-soa-ttl</dt>
<dd>
 
 See the description of
 zero-no-soa-ttl in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>update-check-ksk</dt>
<dd>
 
 See the description of
 update-check-ksk in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>dnssec-loadkeys-interval</dt>
<dd>
 
 See the description of
 dnssec-loadkeys-interval in <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called &#8220;options Statement Definition and
 Usage&#8221;</a>.
 
 </dd>
<dt>dnssec-update-mode</dt>
<dd>
 
 See the description of
 dnssec-update-mode in <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called &#8220;options Statement Definition and
 Usage&#8221;</a>.
 
 </dd>
<dt>dnssec-dnskey-kskonly</dt>
<dd>
 
 See the description of
 dnssec-dnskey-kskonly in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>try-tcp-refresh</dt>
<dd>
 
 See the description of
 try-tcp-refresh in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>database</dt>
<dd>
 
 Specify the type of database to be used for storing the
 zone data. The string following the database 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.
 
 
 The default is <code>"rbt"</code>, BIND 9's
 native in-memory
 red-black-tree database. This database does not take
 arguments.
 
 
 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.
 
 </dd>
<dt>dialup</dt>
<dd>
 
 See the description of
 dialup in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>delegation-only</dt>
<dd>
 
 The flag only applies to forward, hint and stub
 zones. If set to <code>yes</code>,
 then the zone will also be treated as if it is
 also a delegation-only type zone.
 
 
 See caveats in <a class="xref" href="Bv9ARM.ch06.html#root_delegation_only">root-delegation-only</a>.
 
 </dd>
<dt>file</dt>
<dd>
 
 Set the zone's filename. In master,
 hint, and redirect
 zones which do not have masters
 defined, zone data is loaded from this file. In
 slave, stub, and
 redirect zones which do have
 masters defined, zone data is
 retrieved from another server and saved in this file.
 This option is not applicable to other zone types.
 
 </dd>
<dt>forward</dt>
<dd>
 
 Only meaningful if the zone has a forwarders
 list. The only value causes
 the lookup to fail
 after trying the forwarders and getting no answer, while first would
 allow a normal lookup to be tried.
 
 </dd>
<dt>forwarders</dt>
<dd>
 
 Used to override the list of global forwarders.
 If it is not specified in a zone of type forward,
 no forwarding is done for the zone and the global options are
 not used.
 
 </dd>
<dt>ixfr-base</dt>
<dd>
 
 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.
 
 </dd>
<dt>ixfr-tmp-file</dt>
<dd>
 
 Was an undocumented option in <acronym class="acronym">BIND</acronym> 8.
 Ignored in <acronym class="acronym">BIND</acronym> 9.
 
 </dd>
<dt>journal</dt>
<dd>
 
 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 master and slave zones.
 
 </dd>
<dt>max-journal-size</dt>
<dd>
 
 See the description of
 max-journal-size in <a class="xref" href="Bv9ARM.ch06.html#server_resource_limits" title="Server Resource Limits">the section called &#8220;Server Resource Limits&#8221;</a>.
 
 </dd>
<dt>max-records</dt>
<dd>
 
 See the description of
 max-records in <a class="xref" href="Bv9ARM.ch06.html#server_resource_limits" title="Server Resource Limits">the section called &#8220;Server Resource Limits&#8221;</a>.
 
 </dd>
<dt>max-transfer-time-in</dt>
<dd>
 
 See the description of
 max-transfer-time-in in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
 
 </dd>
<dt>max-transfer-idle-in</dt>
<dd>
 
 See the description of
 max-transfer-idle-in in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
 
 </dd>
<dt>max-transfer-time-out</dt>
<dd>
 
 See the description of
 max-transfer-time-out in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
 
 </dd>
<dt>max-transfer-idle-out</dt>
<dd>
 
 See the description of
 max-transfer-idle-out in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
 
 </dd>
<dt>notify</dt>
<dd>
 
 See the description of
 notify in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>notify-delay</dt>
<dd>
 
 See the description of
 notify-delay in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
 
 </dd>
<dt>notify-to-soa</dt>
<dd>
 
 See the description of
 notify-to-soa in
 <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>pubkey</dt>
<dd>
 
 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.
 
 </dd>
<dt>zone-statistics</dt>
<dd>
 
 See the description of
 zone-statistics in
 <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called &#8220;options Statement Definition and
 Usage&#8221;</a>.
 
 </dd>
<dt>server-addresses</dt>
<dd>
 
 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.
 
 
 For example, if "example.com" is configured as a
 static-stub zone with 192.0.2.1 and 2001:db8::1234
 in a server-addresses option,
 the following RRs will be internally configured.
 
<pre class="programlisting">example.com. NS example.com.
example.com. A 192.0.2.1
example.com. AAAA 2001:db8::1234</pre>
 
 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.
 
 </dd>
<dt>server-names</dt>
<dd>
 
 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
 named 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
 server-names option, but
 "ns.example.net" cannot, and will be rejected by
 the configuration parser.
 
 
 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 server-names option,
 the following RRs will be internally configured.
 
<pre class="programlisting">example.com. NS ns1.example.net.
example.com. NS ns2.example.net.
</pre>
 
 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.
 
 </dd>
<dt>sig-validity-interval</dt>
<dd>
 
 See the description of
 sig-validity-interval in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
 
 </dd>
<dt>sig-signing-nodes</dt>
<dd>
 
 See the description of
 sig-signing-nodes in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
 
 </dd>
<dt>sig-signing-signatures</dt>
<dd>
 
 See the description of
 sig-signing-signatures in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
 
 </dd>
<dt>sig-signing-type</dt>
<dd>
 
 See the description of
 sig-signing-type in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
 
 </dd>
<dt>transfer-source</dt>
<dd>
 
 See the description of
 transfer-source in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
 
 </dd>
<dt>transfer-source-v6</dt>
<dd>
 
 See the description of
 transfer-source-v6 in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
 
 </dd>
<dt>alt-transfer-source</dt>
<dd>
 
 See the description of
 alt-transfer-source in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
 
 </dd>
<dt>alt-transfer-source-v6</dt>
<dd>
 
 See the description of
 alt-transfer-source-v6 in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
 
 </dd>
<dt>use-alt-transfer-source</dt>
<dd>
 
 See the description of
 use-alt-transfer-source in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
 
 </dd>
<dt>notify-source</dt>
<dd>
 
 See the description of
 notify-source in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
 
 </dd>
<dt>notify-source-v6</dt>
<dd>
 
 See the description of
 notify-source-v6 in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>.
 
 </dd>
<dt>
min-refresh-time, max-refresh-time, min-retry-time, max-retry-time
</dt>
<dd>
 
 See the description in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
 
 </dd>
<dt>ixfr-from-differences</dt>
<dd>
 
 See the description of
 ixfr-from-differences in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 (Note that the ixfr-from-differences
 <code>master</code> and
 <code>slave</code> choices are not
 available at the zone level.)
 
 </dd>
<dt>key-directory</dt>
<dd>
 
 See the description of
 key-directory in <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called &#8220;options Statement Definition and
 Usage&#8221;</a>.
 
 </dd>
<dt>auto-dnssec</dt>
<dd>
 
 See the description of
 auto-dnssec in
 <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called &#8220;options Statement Definition and
 Usage&#8221;</a>.
 
 </dd>
<dt>serial-update-method</dt>
<dd>
 
 See the description of
 serial-update-method in
 <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called &#8220;options Statement Definition and
 Usage&#8221;</a>.
 
 </dd>
<dt>inline-signing</dt>
<dd>
 
 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
 behavior is disabled by default.
 
 </dd>
<dt>multi-master</dt>
<dd>
 
 See the description of multi-master in
 <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
<dt>masterfile-format</dt>
<dd>
 
 See the description of masterfile-format
 in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called &#8220;Tuning&#8221;</a>.
 
 </dd>
<dt>max-zone-ttl</dt>
<dd>
 
 See the description of max-zone-ttl
 in <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called &#8220;options Statement Definition and
 Usage&#8221;</a>.
 
 </dd>
<dt>dnssec-secure-to-insecure</dt>
<dd>
 
 See the description of
 dnssec-secure-to-insecure in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a>.
 
 </dd>
</dl></div>

</div>
 <div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="dynamic_update_policies"></a>Dynamic Update Policies</h4></div></div></div>

<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
 allow-update and
 update-policy option, respectively.
 
 
 The allow-update clause is a simple
 access control list. Any client that matches
 the ACL is granted permission to update any record
 in the zone.
 
 
 The update-policy clause
 allows more fine-grained control over what updates are
 allowed. It specifies a set of rules, in which each rule
 either grants or denies permission for one or more
 names in the zone to be updated by one or more
 identities. Identity is determined by the key that
 signed the update request using either TSIG or SIG(0).
 In most cases, update-policy rules
 only apply to key-based identities. There is no way
 to specify update permissions based on client source
 address.
 
 
 update-policy rules are only meaningful
 for zones of type master, and are
 not allowed in any other zone type.
 It is a configuration error to specify both
 allow-update and
 update-policy at the same time.
 
 
 A pre-defined update-policy rule can be
 switched on with the command
 update-policy local;.
 Using this in a zone causes
 named to generate a TSIG session key
 when starting up and store it in a file; this key can then
 be used by local clients to update the zone while
 named is running.
 By default, the session key is stored in the file
 <code class="filename">/var/run/named/session.key</code>, the key name
 is "local-ddns", and the key algorithm is HMAC-SHA256.
 These values are configurable with the
 session-keyfile,
 session-keyname and
 session-keyalg options, respectively.
 A client running on the local system, if run with appropriate
 permissions, may read the session key from the key file and
 use it 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:

<pre class="programlisting">update-policy { grant local-ddns zonesub any; };
 </pre>

...with the additional restriction that only clients
 connecting from the local system will be permitted to send
 updates.
 
 
 Note that only one session key is generated by
 named; all zones configured to use
 update-policy local will accept the same key.
 
 
 The command nsupdate -l implements this
 feature, sending requests to localhost and signing them using
 the key retrieved from the session key file.

Other rule definitions look like this:

<pre class="programlisting">
( grant | deny ) <code>identity</code> <code>ruletype</code> [ <code>name</code> ] [ <code>types</code> ]
</pre>

Each rule grants or denies privileges. Rules are checked
 in the order in which they are specified in the
 update-policy statement. Once a message
 has successfully matched a rule, the operation is immediately
 granted or denied, and no further rules are examined. There
 are 13 types of rules; the rule type is specified by the
 ruletype field, and the interpretation
 of other fields varies depending on the rule type.
 
 
 In general, a rule is matched when the
 key that signed an update request matches the
 identity field, the name of the record
 to be updated matches the name field
 (in the manner specified by the ruletype
 field), and the type of the record to be updated matches the
 types field. Details for each rule type
 are described below.
 
 
 The identity field must be set to
 a fully-qualified domain name. In most cases, this
 represensts the name of the TSIG or SIG(0) key that must be
 used to sign the update request. If the specified name is a
 wildcard, it is subject to DNS wildcard expansion, and the
 rule may apply to multiple identities. When a TKEY exchange
 has been used to create a shared secret, the identity of
 the key used to authenticate the TKEY exchange will be
 used as the identity of the shared secret. Some rule types
 use identities matching the client's Kerberos principal
 (e.g, <code>"host/machine@REALM"</code>) or
 Windows realm (<code>machine$@REALM</code>).
 
 
 The <code>name</code> field also specifies
 a fully-qualified domain name. This often
 represents the name of the record to be updated.
 Interpretation of this field is dependent on rule type.
 
 
 If no types are explicitly specified,
 then a 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.
 
 
 The <code>ruletype</code> 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>.
 
 <div class="informaltable">
 <table border="1">
<colgroup>
<col width="0.819in" class="1">
<col width="3.681in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 
 <code class="varname">name</code>
 
 </td>
<td>
 
 Exact-match semantics. This rule matches
 when the name being updated is identical
 to the contents of the
 <code>name</code> field.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">subdomain</code>
 
 </td>
<td>
 
 This rule matches when the name being updated
 is a subdomain of, or identical to, the
 contents of the <code>name</code>
 field.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">zonesub</code>
 
 </td>
<td>
 
 This rule is similar to subdomain, except that
 it matches when the name being updated is a
 subdomain of the zone in which the
 update-policy statement
 appears. This obviates the need to type the zone
 name twice, and enables the use of a standard
 update-policy statement in
 multiple zones without modification.
 
 
 When this rule is used, the
 <code>name</code> field is omitted.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">wildcard</code>
 
 </td>
<td>
 
 The <code>name</code> field
 is subject to DNS wildcard expansion, and
 this rule matches when the name being updated
 is a valid expansion of the wildcard.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">self</code>
 
 </td>
<td>
 
 This rule matches when the name of the record
 being updated matches the contents of the
 <code>identity</code> field.
 The <code>name</code> field
 is ignored. To avoid confusion, it is recommended
 that this field be set to the same value as the
 <code>identity</code> field or to
 "."
 
 
 The <code class="varname">self</code> rule type is
 most useful when allowing one key per
 name to update, where the key has the same
 name as the record to be updated. In this case,
 the <code>identity</code> field
 can be specified as <code class="constant">*</code>
 (an asterisk).
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">selfsub</code>
 
 </td>
<td>
 
 This rule is similar to <code class="varname">self</code>
 except that subdomains of <code class="varname">self</code>
 can also be updated.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">selfwild</code>
 
 </td>
<td>
 
 This rule is similar to <code class="varname">self</code>
 except that only subdomains of
 <code class="varname">self</code> can be updated.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">ms-self</code>
 
 </td>
<td>
 
 When a client sends an UPDATE using a Windows
 machine principal (for example, 'machine$@REALM'),
 this rule allows records with the absolute name
 of 'machine.REALM' to be updated.
 
 
 The realm to be matched is specified in the
 <code>identity</code> field.
 
 
 The <code>name</code> field has
 no effect on this rule; it should be set to "."
 as a placeholder.
 
 
 For example,
 <code>grant EXAMPLE.COM ms-self . A AAAA</code>
 allows any machine with a valid principal in
 the realm <code>EXAMPLE.COM</code> to update
 its own address records.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">ms-subdomain</code>
 
 </td>
<td>
 
 When a client sends an UPDATE using a Windows
 machine principal (for example, 'machine$@REALM'),
 this rule allows any machine in the specified
 realm to update any record in the zone or in a
 specified subdomain of the zone.
 
 
 The realm to be matched is specified in the
 <code>identity</code> field.
 
 
 The <code>name</code> field
 specifies the subdomain that may be updated.
 If set to "." (or any other name at or above
 the zone apex), any name in the zone can be
 updated.
 
 
 For example, if update-policy
 for the zone "example.com" includes
 <code>grant EXAMPLE.COM ms-subdomain hosts.example.com. A AAAA</code>,
 any machine with a valid principal in
 the realm <code>EXAMPLE.COM</code> will
 be able to update address records at or below
 "hosts.example.com".
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">krb5-self</code>
 
 </td>
<td>
 
 When a client sends an UPDATE using a
 Kerberos machine principal (for example,
 'host/machine@REALM'), this rule allows
 records with the absolute name of 'machine'
 to be updated provided it has been authenticated
 by REALM. This is similar but not identical
 to ms-self due to the
 'machine' part of the Kerberos principal
 being an absolute name instead of a unqualified
 name.
 
 
 The realm to be matched is specified in the
 <code>identity</code> field.
 
 
 The <code>name</code> field has
 no effect on this rule; it should be set to "."
 as a placeholder.
 
 
 For example,
 <code>grant EXAMPLE.COM krb5-self . A AAAA</code>
 allows any machine with a valid principal in
 the realm <code>EXAMPLE.COM</code> to update
 its own address records.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">krb5-subdomain</code>
 
 </td>
<td>
 
 This rule is identical to
 ms-subdomain, except that it works
 with Kerberos machine principals (i.e.,
 'host/machine@REALM') rather than Windows machine
 principals.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">tcp-self</code>
 
 </td>
<td>
 
 This rule allows updates that have been sent via
 TCP and for which the standard mapping from the
 client's IP address into the
 <code class="literal">in-addr.arpa</code> and
 <code class="literal">ip6.arpa</code>
 namespaces match the name to be updated.
 The identity field must match
 that name. The name field
 should be set to ".".
 Note that, since identity is based on the client's
 IP address, it is not necessary for update request
 messages to be signed.
 
 <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>
 
 <code class="varname">6to4-self</code>
 
 </td>
<td>
 
 This allows the name matching a 6to4 IPv6 prefix,
 as specified in RFC 3056, to be updated by any
 TCP connection from either the 6to4 network or
 from the corresponding IPv4 address. This is
 intended to allow NS or DNAME RRsets to be added
 to the <code class="literal">ip6.arpa</code> reverse tree.
 
 
 The identity field must match
 the 6to4 prefix in <code class="literal">ip6.arpa</code>.
 The name field should
 be set to ".".
 Note that, since identity is based on the client's
 IP address, it is not necessary for update request
 messages to be signed.
 
 
 In addition, if specified for an
 <code class="literal">ip6.arpa</code> name outside of the
 <code class="literal">2.0.0.2.ip6.arpa</code> namespace,
 the corresponding /48 reverse name can be updated.
 For example, TCP/IPv6 connections
 from 2001:DB8:ED0C::/48 can update records at
 <code class="literal">C.0.D.E.8.B.D.0.1.0.0.2.ip6.arpa</code>.
 
 <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>
 
 <code class="varname">external</code>
 
 </td>
<td>
 
 This rule allows named
 to defer the decision of whether to allow a
 given update to an external daemon.
 
 
 The method of communicating with the daemon is
 specified in the <code>identity</code>
 field, the format of which is
 "<code class="constant">local:</code><code>path</code>",
 where <code>path</code> is the location
 of a UNIX-domain socket. (Currently, "local" is the
 only supported mechanism.)
 
 
 Requests to the external daemon are sent over the
 UNIX-domain socket as datagrams with the following
 format:
 
 <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>
 
 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.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="multiple_views"></a>Multiple views</h4></div></div></div>

When multiple views are in use, a zone may be
 referenced by more than one of them. Often, the views
 will contain different zones with the same name, allowing
 different clients to receive different answers for the same
 queries. At times, however, it is desirable for multiple
 views to contain identical zones. The
 in-view zone option provides an efficient
 way to do this: it allows a view to reference a zone that
 was defined in a previously configured view. Example:
 
 <pre class="programlisting">
view internal {
 match-clients { 10/8; };

zone example.com {
        type master;
        file "example-external.db";
    };
};

view external {
    match-clients { any; };

zone example.com {
 in-view internal;
 };
};
 </pre>
 
 An in-view option cannot refer to a view
 that is configured later in the configuration file.
 
 
 A zone statement which uses the
 in-view option may not use any other
 options with the exception of forward
 and forwarders. (These options control
 the behavior of the containing view, rather than changing
 the zone object itself.)
 
 
 Zone level acls (e.g. allow-query, allow-transfer) and
 other configuration details of the zone are all set
 in the view the referenced zone is defined in. Care
 need to be taken to ensure that acls are wide enough
 for all views referencing the zone.
 
 
 An in-view zone cannot be used as a
 response policy zone.
 
 
 An in-view zone is not intended to reference
 a forward zone.
 
 </div>

</div>
 </div>
 <div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="zone_file"></a>Zone File</h2></div></div></div>

<div class="section">
<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>

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.
 
 <div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.7.6.2.3"></a>Resource Records</h4></div></div></div>

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 class="xref" href="Bv9ARM.ch06.html#the_sortlist_statement" title="The sortlist Statement">the section called &#8220;The sortlist Statement&#8221;</a> and <a class="xref" href="Bv9ARM.ch06.html#rrset_ordering" title="RRset Ordering">the section called &#8220;RRset Ordering&#8221;</a>.

The components of a Resource Record are:
 
 <div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.000in" class="1">
<col width="3.500in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 
 owner name
 
 </td>
<td>
 
 The domain name where the RR is found.
 
 </td>
</tr>
<tr>
<td>
 
 type
 
 </td>
<td>
 
 An encoded 16-bit value that specifies
 the type of the resource record.
 
 </td>
</tr>
<tr>
<td>
 
 TTL
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 class
 
 </td>
<td>
 
 An encoded 16-bit value that identifies
 a protocol family or instance of a protocol.
 
 </td>
</tr>
<tr>
<td>
 
 RDATA
 
 </td>
<td>
 
 The resource data. The format of the
 data is type (and sometimes class) specific.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 
 The following are types of valid RRs:
 
 <div class="informaltable">
 <table border="1">
<colgroup>
<col width="0.875in" class="1">
<col width="3.625in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 
 A
 
 </td>
<td>
 
 A host address. In the IN class, this is a
 32-bit IP address. Described in RFC 1035.
 
 </td>
</tr>
<tr>
<td>
 
 AAAA
 
 </td>
<td>
 
 IPv6 address. Described in RFC 1886.
 
 </td>
</tr>
<tr>
<td>
 
 A6
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 AFSDB
 
 </td>
<td>
 
 Location of AFS database servers.
 Experimental. Described in RFC 1183.
 
 </td>
</tr>
<tr>
<td>
 
 APL
 
 </td>
<td>
 
 Address prefix list. Experimental.
 Described in RFC 3123.
 
 </td>
</tr>
<tr>
<td>
 
 ATMA
 
 </td>
<td>
 
 ATM Address.
 
 </td>
</tr>
<tr>
<td>
 
 AVC
 
 </td>
<td>
 
 Application Visibility and Control record.
 
 </td>
</tr>
<tr>
<td>
 
 CAA
 
 </td>
<td>
 
 Identifies which Certificate Authorities can issue
 certificates for this domain and what rules they
 need to follow when doing so. Defined in RFC 6844.
 
 </td>
</tr>
<tr>
<td>
 
 CDNSKEY
 
 </td>
<td>
 
 Identifies which DNSKEY records should be published
 as DS records in the parent zone.
 
 </td>
</tr>
<tr>
<td>
 
 CDS
 
 </td>
<td>
 
 Contains the set of DS records that should be published
 by the parent zone.
 
 </td>
</tr>
<tr>
<td>
 
 CERT
 
 </td>
<td>
 
 Holds a digital certificate.
 Described in RFC 2538.
 
 </td>
</tr>
<tr>
<td>
 
 CNAME
 
 </td>
<td>
 
 Identifies the canonical name of an alias.
 Described in RFC 1035.
 
 </td>
</tr>
<tr>
<td>
 
 CSYNC
 
 </td>
<td>
 
 Child-to-Parent Synchronization in DNS as described
 in RFC 7477.
 
 </td>
</tr>
<tr>
<td>
 
 DHCID
 
 </td>
<td>
 
 Is used for identifying which DHCP client is
 associated with this name. Described in RFC 4701.
 
 </td>
</tr>
<tr>
<td>
 
 DLV
 
 </td>
<td>
 
 A DNS Look-aside Validation record which contains
 the records that are used as trust anchors for
 zones in a DLV namespace. Described in RFC 4431.
 
 </td>
</tr>
<tr>
<td>
 
 DNAME
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 DNSKEY
 
 </td>
<td>
 
 Stores a public key associated with a signed
 DNS zone. Described in RFC 4034.
 
 </td>
</tr>
<tr>
<td>
 
 DOA
 
 </td>
<td>
 
 Implements the Digital Object Architecture over
 DNS. Experimental.
 
 </td>
</tr>
<tr>
<td>
 
 DS
 
 </td>
<td>
 
 Stores the hash of a public key associated with a
 signed DNS zone. Described in RFC 4034.
 
 </td>
</tr>
<tr>
<td>
 
 EID
 
 </td>
<td>
 
 End Point Identifier.
 
 </td>
</tr>
<tr>
<td>
 
 EUI48
 
 </td>
<td>
 
 A 48-bit EUI address. Described in RFC 7043.
 
 </td>
</tr>
<tr>
<td>
 
 EUI64
 
 </td>
<td>
 
 A 64-bit EUI address. Described in RFC 7043.
 
 </td>
</tr>
<tr>
<td>
 
 GID
 
 </td>
<td>
 
 Reserved.
 
 </td>
</tr>
<tr>
<td>
 
 GPOS
 
 </td>
<td>
 
 Specifies the global position. Superseded by LOC.
 
 </td>
</tr>
<tr>
<td>
 
 HINFO
 
 </td>
<td>
 
 Identifies the CPU and OS used by a host.
 Described in RFC 1035.
 
 </td>
</tr>
<tr>
<td>
 
 HIP
 
 </td>
<td>
 
 Host Identity Protocol Address.
 Described in RFC 5205.
 
 </td>
</tr>
<tr>
<td>
 
 IPSECKEY
 
 </td>
<td>
 
 Provides a method for storing IPsec keying material in
 DNS. Described in RFC 4025.
 
 </td>
</tr>
<tr>
<td>
 
 ISDN
 
 </td>
<td>
 
 Representation of ISDN addresses.
 Experimental. Described in RFC 1183.
 
 </td>
</tr>
<tr>
<td>
 
 KEY
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 KX
 
 </td>
<td>
 
 Identifies a key exchanger for this
 DNS name. Described in RFC 2230.
 
 </td>
</tr>
<tr>
<td>
 
 L32
 
 </td>
<td>
 
 Holds 32-bit Locator values for
 Identifier-Locator Network Protocol. Described
 in RFC 6742.
 
 </td>
</tr>
<tr>
<td>
 
 L64
 
 </td>
<td>
 
 Holds 64-bit Locator values for
 Identifier-Locator Network Protocol. Described
 in RFC 6742.
 
 </td>
</tr>
<tr>
<td>
 
 LOC
 
 </td>
<td>
 
 For storing GPS info. Described in RFC 1876.
 Experimental.
 
 </td>
</tr>
<tr>
<td>
 
 LP
 
 </td>
<td>
 
 Identifier-Locator Network Protocol.
 Described in RFC 6742.
 
 </td>
</tr>
<tr>
<td>
 
 MB
 
 </td>
<td>
 
 Mail Box. Historical.
 
 </td>
</tr>
<tr>
<td>
 
 MD
 
 </td>
<td>
 
 Mail Destination. Historical.
 
 </td>
</tr>
<tr>
<td>
 
 MF
 
 </td>
<td>
 
 Mail Forwarder. Historical.
 
 </td>
</tr>
<tr>
<td>
 
 MG
 
 </td>
<td>
 
 Mail Group. Historical.
 
 </td>
</tr>
<tr>
<td>
 
 MINFO
 
 </td>
<td>
 
 Mail Information.
 
 </td>
</tr>
<tr>
<td>
 
 MR
 
 </td>
<td>
 
 Mail Rename. Historical.
 
 </td>
</tr>
<tr>
<td>
 
 MX
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 NAPTR
 
 </td>
<td>
 
 Name authority pointer. Described in RFC 2915.
 
 </td>
</tr>
<tr>
<td>
 
 NID
 
 </td>
<td>
 
 Holds values for Node Identifiers in
 Identifier-Locator Network Protocol. Described
 in RFC 6742.
 
 </td>
</tr>
<tr>
<td>
 
 NINFO
 
 </td>
<td>
 
 Contains zone status information.
 
 </td>
</tr>
<tr>
<td>
 
 NIMLOC
 
 </td>
<td>
 
 Nimrod Locator.
 
 </td>
</tr>
<tr>
<td>
 
 NSAP
 
 </td>
<td>
 
 A network service access point.
 Described in RFC 1706.
 
 </td>
</tr>
<tr>
<td>
 
 NSAP-PTR
 
 </td>
<td>
 
 Historical.
 
 </td>
</tr>
<tr>
<td>
 
 NS
 
 </td>
<td>
 
 The authoritative name server for the
 domain. Described in RFC 1035.
 
 </td>
</tr>
<tr>
<td>
 
 NSEC
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 NSEC3
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 NSEC3PARAM
 
 </td>
<td>
 
 Used in DNSSECbis to tell the authoritative
 server which NSEC3 chains are available to use.
 Described in RFC 5155.
 
 </td>
</tr>
<tr>
<td>
 
 NULL
 
 </td>
<td>
 
 This is an opaque container.
 
 </td>
</tr>
<tr>
<td>
 
 NXT
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 OPENPGPKEY
 
 </td>
<td>
 
 Used to hold an OPENPGPKEY.
 
 </td>
</tr>
<tr>
<td>
 
 PTR
 
 </td>
<td>
 
 A pointer to another part of the domain
 name space. Described in RFC 1035.
 
 </td>
</tr>
<tr>
<td>
 
 PX
 
 </td>
<td>
 
 Provides mappings between RFC 822 and X.400
 addresses. Described in RFC 2163.
 
 </td>
</tr>
<tr>
<td>
 
 RKEY
 
 </td>
<td>
 
 Resource key.
 
 </td>
</tr>
<tr>
<td>
 
 RP
 
 </td>
<td>
 
 Information on persons responsible
 for the domain. Experimental. Described in RFC 1183.
 
 </td>
</tr>
<tr>
<td>
 
 RRSIG
 
 </td>
<td>
 
 Contains DNSSECbis signature data. Described
 in RFC 4034.
 
 </td>
</tr>
<tr>
<td>
 
 RT
 
 </td>
<td>
 
 Route-through binding for hosts that
 do not have their own direct wide area network
 addresses.
 Experimental. Described in RFC 1183.
 
 </td>
</tr>
<tr>
<td>
 
 SIG
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
<tr>
<td>
 
 SINK
 
 </td>
<td>
 
 The kitchen sink record.
 
 </td>
</tr>
<tr>
<td>
 
 SMIMEA
 
 </td>
<td>
 
 The S/MIME Security Certificate Association.
 
 </td>
</tr>
<tr>
<td>
 
 SOA
 
 </td>
<td>
 
 Identifies the start of a zone of authority.
 Described in RFC 1035.
 
 </td>
</tr>
<tr>
<td>
 
 SPF
 
 </td>
<td>
 
 Contains the Sender Policy Framework information
 for a given email domain. Described in RFC 4408.
 
 </td>
</tr>
<tr>
<td>
 
 SRV
 
 </td>
<td>
 
 Information about well known network
 services (replaces WKS). Described in RFC 2782.
 
 </td>
</tr>
<tr>
<td>
 
 SSHFP
 
 </td>
<td>
 
 Provides a way to securely publish a secure shell key's
 fingerprint. Described in RFC 4255.
 
 </td>
</tr>
<tr>
<td>
 
 TA
 
 </td>
<td>
 
 Trust Anchor. Experimental.
 
 </td>
</tr>
<tr>
<td>
 
 TALINK
 
 </td>
<td>
 
 Trust Anchor Link. Experimental.
 
 </td>
</tr>
<tr>
<td>
 
 TLSA
 
 </td>
<td>
 
 Transport Layer Security Certificate Association.
 Described in RFC 6698.
 
 </td>
</tr>
<tr>
<td>
 
 TXT
 
 </td>
<td>
 
 Text records. Described in RFC 1035.
 
 </td>
</tr>
<tr>
<td>
 
 UID
 
 </td>
<td>
 
 Reserved.
 
 </td>
</tr>
<tr>
<td>
 
 UINFO
 
 </td>
<td>
 
 Reserved.
 
 </td>
</tr>
<tr>
<td>
 
 UNSPEC
 
 </td>
<td>
 
 Reserved. Historical.
 
 </td>
</tr>
<tr>
<td>
 
 URI
 
 </td>
<td>
 
 Holds a URI. Described in RFC 7553.
 
 </td>
</tr>
<tr>
<td>
 
 WKS
 
 </td>
<td>
 
 Information about which well known
 network services, such as SMTP, that a domain
 supports. Historical.
 
 </td>
</tr>
<tr>
<td>
 
 X25
 
 </td>
<td>
 
 Representation of X.25 network addresses.
 Experimental. Described in RFC 1183.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 
 The following classes of resource records
 are currently valid in the DNS:
 
 <div class="informaltable">
<table border="1">
<colgroup>
<col width="0.875in" class="1">
<col width="3.625in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 
 IN
 
 </td>
<td>
 
 The Internet.
 
 </td>
</tr>
<tr>
<td>
 
 CH
 
 </td>
<td>
 
 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>.
 
 </td>
</tr>
<tr>
<td>
 
 HS
 
 </td>
<td>
 
 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.
 
 </td>
</tr>
</tbody>
</table>
 </div>

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.
 
 
 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.
 
 
 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.
 
 </div>
 <div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="rr_text"></a>Textual expression of RRs</h4></div></div></div>

RRs are represented in binary form in the packets of the DNS
 protocol, and are usually represented in highly encoded form
 when
 stored in a name server or resolver. In the examples provided
 in
 RFC 1034, a style similar to that used in master files was
 employed
 in order to show the contents of RRs. In this format, most RRs
 are shown on a single line, although continuation lines are
 possible
 using parentheses.
 
 
 The start of the line gives the owner of the RR. If a line
 begins with a blank, then the owner is assumed to be the same as
 that of the previous RR. Blank lines are often included for
 readability.
 
 
 Following the owner, we list the TTL, type, and class of the
 RR. Class and type use the mnemonics defined above, and TTL is
 an integer before the type field. In order to avoid ambiguity
 in
 parsing, type and class mnemonics are disjoint, TTLs are
 integers,
 and the type mnemonic is always last. The IN class and TTL
 values
 are often omitted from examples in the interests of clarity.
 
 
 The resource data or RDATA section of the RR are given using
 knowledge of the typical representation for the data.
 
 
 For example, we might show the RRs carried in a message as:
 
 <div class="informaltable">
<table border="1">
<colgroup>
<col width="1.381in" class="1">
<col width="1.020in" class="2">
<col width="2.099in" class="3">
</colgroup>
<tbody>
<tr>
<td>
 
 <code class="literal">ISI.EDU.</code>
 
 </td>
<td>
 
 <code class="literal">MX</code>
 
 </td>
<td>
 
 <code class="literal">10 VENERA.ISI.EDU.</code>
 
 </td>
</tr>
<tr>
<td>
 
 </td>
<td>
 
 <code class="literal">MX</code>
 
 </td>
<td>
 
 <code class="literal">10 VAXA.ISI.EDU</code>
 
 </td>
</tr>
<tr>
<td>
 
 <code class="literal">VENERA.ISI.EDU</code>
 
 </td>
<td>
 
 <code class="literal">A</code>
 
 </td>
<td>
 
 <code class="literal">128.9.0.32</code>
 
 </td>
</tr>
<tr>
<td>
 
 </td>
<td>
 
 <code class="literal">A</code>
 
 </td>
<td>
 
 <code class="literal">10.1.0.52</code>
 
 </td>
</tr>
<tr>
<td>
 
 <code class="literal">VAXA.ISI.EDU</code>
 
 </td>
<td>
 
 <code class="literal">A</code>
 
 </td>
<td>
 
 <code class="literal">10.2.0.27</code>
 
 </td>
</tr>
<tr>
<td>
 
 </td>
<td>
 
 <code class="literal">A</code>
 
 </td>
<td>
 
 <code class="literal">128.9.0.33</code>
 
 </td>
</tr>
</tbody>
</table>
 </div>
 
 The MX RRs have an RDATA section which consists of a 16-bit
 number followed by a domain name. The address RRs use a
 standard
 IP address format to contain a 32-bit internet address.
 
 
 The above example shows six RRs, with two RRs at each of three
 domain names.
 
 
 Similarly we might see:
 
 <div class="informaltable">
<table border="1">
<colgroup>
<col width="1.491in" class="1">
<col width="1.067in" class="2">
<col width="2.067in" class="3">
</colgroup>
<tbody>
<tr>
<td>
 
 <code class="literal">XX.LCS.MIT.EDU.</code>
 
 </td>
<td>
 
 <code class="literal">IN A</code>
 
 </td>
<td>
 
 <code class="literal">10.0.0.44</code>
 
 </td>
</tr>
<tr>
<td> </td>
<td>
 
 <code class="literal">CH A</code>
 
 </td>
<td>
 
 <code class="literal">MIT.EDU. 2420</code>
 
 </td>
</tr>
</tbody>
</table>
 </div>
 
 This example shows two addresses for
 <code class="literal">XX.LCS.MIT.EDU</code>, each of a different class.
 
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="mx_records"></a>Discussion of MX Records</h3></div></div></div>

As described above, domain servers store information as a
 series of resource records, each of which contains a particular
 piece of information about a given domain name (which is usually,
 but not always, a host). The simplest way to think of a RR is as
 a typed pair of data, a domain name matched with a relevant datum,
 and stored with some additional type information to help systems
 determine when the RR is relevant.

MX records are used to control delivery of email. The data
 specified in the record is a priority and a domain name. The
 priority
 controls the order in which email delivery is attempted, with the
 lowest number first. If two priorities are the same, a server is
 chosen randomly. If no servers at a given priority are responding,
 the mail transport agent will fall back to the next largest
 priority.
 Priority numbers do not have any absolute meaning &#8212; they are
 relevant
 only respective to other MX records for that domain name. The
 domain
 name given is the machine to which the mail will be delivered.
 It must have an associated address record
 (A or AAAA) &#8212; CNAME is not sufficient.
 
 
 For a given domain, if there is both a CNAME record and an
 MX record, the MX record is in error, and will be ignored.
 Instead,
 the mail will be delivered to the server specified in the MX
 record
 pointed to by the CNAME.
 For example:
 
 <div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.708in" class="1">
<col width="0.444in" class="2">
<col width="0.444in" class="3">
<col width="0.976in" class="4">
<col width="1.553in" class="5">
</colgroup>
<tbody>
<tr>
<td>
 
 <code class="literal">example.com.</code>
 
 </td>
<td>
 
 <code class="literal">IN</code>
 
 </td>
<td>
 
 <code class="literal">MX</code>
 
 </td>
<td>
 
 <code class="literal">10</code>
 
 </td>
<td>
 
 <code class="literal">mail.example.com.</code>
 
 </td>
</tr>
<tr>
<td>
 
 </td>
<td>
 
 <code class="literal">IN</code>
 
 </td>
<td>
 
 <code class="literal">MX</code>
 
 </td>
<td>
 
 <code class="literal">10</code>
 
 </td>
<td>
 
 <code class="literal">mail2.example.com.</code>
 
 </td>
</tr>
<tr>
<td>
 
 </td>
<td>
 
 <code class="literal">IN</code>
 
 </td>
<td>
 
 <code class="literal">MX</code>
 
 </td>
<td>
 
 <code class="literal">20</code>
 
 </td>
<td>
 
 <code class="literal">mail.backup.org.</code>
 
 </td>
</tr>
<tr>
<td>
 
 <code class="literal">mail.example.com.</code>
 
 </td>
<td>
 
 <code class="literal">IN</code>
 
 </td>
<td>
 
 <code class="literal">A</code>
 
 </td>
<td>
 
 <code class="literal">10.0.0.1</code>
 
 </td>
<td>
 
 </td>
</tr>
<tr>
<td>
 
 <code class="literal">mail2.example.com.</code>
 
 </td>
<td>
 
 <code class="literal">IN</code>
 
 </td>
<td>
 
 <code class="literal">A</code>
 
 </td>
<td>
 
 <code class="literal">10.0.0.2</code>
 
 </td>
<td>
 
 </td>
</tr>
</tbody>
</table>
 </div>

 Mail delivery will be attempted to <code class="literal">mail.example.com</code> and
 <code class="literal">mail2.example.com</code> (in
 any order), and if neither of those succeed, delivery to <code class="literal">mail.backup.org</code> will
 be attempted.
 
 </div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="Setting_TTLs"></a>Setting TTLs</h3></div></div></div>

The time-to-live of the RR field is a 32-bit integer represented
 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. The following three types of TTL are
 currently
 used in a zone file.
 
 <div class="informaltable">
 <table border="1">
<colgroup>
<col width="0.750in" class="1">
<col width="4.375in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 
 SOA
 
 </td>
<td>
 
 The last field in the SOA is the negative
 caching TTL. This controls how long other servers will
 cache no-such-domain
 (NXDOMAIN) responses from you.
 
 
 The maximum time for
 negative caching is 3 hours (3h).
 
 </td>
</tr>
<tr>
<td>
 
 $TTL
 
 </td>
<td>
 
 The $TTL directive at the top of the
 zone file (before the SOA) gives a default TTL for every
 RR without
 a specific TTL set.
 
 </td>
</tr>
<tr>
<td>
 
 RR TTLs
 
 </td>
<td>
 
 Each RR can have a TTL as the second
 field in the RR, which will control how long other
 servers can cache it.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 
 All of these TTLs default to units of seconds, though units
 can be explicitly specified, for example, <code class="literal">1h30m</code>.
 
 </div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="ipv4_reverse"></a>Inverse Mapping in IPv4</h3></div></div></div>

Reverse name resolution (that is, translation from IP address
 to name) is achieved by means of the in-addr.arpa domain
 and PTR records. Entries in the in-addr.arpa domain are made in
 least-to-most significant order, read left to right. This is the
 opposite order to the way IP addresses are usually written. Thus,
 a machine with an IP address of 10.1.2.3 would have a
 corresponding
 in-addr.arpa name of
 3.2.1.10.in-addr.arpa. This name should have a PTR resource record
 whose data field is the name of the machine or, optionally,
 multiple
 PTR records if the machine has more than one name. For example,
 in the [example.com] domain:
 
 <div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.125in" class="1">
<col width="4.000in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 
 <code class="literal">$ORIGIN</code>
 
 </td>
<td>
 
 <code class="literal">2.1.10.in-addr.arpa</code>
 
 </td>
</tr>
<tr>
<td>
 
 <code class="literal">3</code>
 
 </td>
<td>
 
 <code class="literal">IN PTR foo.example.com.</code>
 
 </td>
</tr>
</tbody>
</table>
 </div>
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 The $ORIGIN lines in the examples
 are for providing context to the examples only &#8212; they do not
 necessarily
 appear in the actual usage. They are only used here to indicate
 that the example is relative to the listed origin.
 
 </div>
 </div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="zone_directives"></a>Other Zone File Directives</h3></div></div></div>

The Master File Format was initially defined in RFC 1035 and
 has subsequently been extended. While the Master File Format
 itself
 is class independent all records in a Master File must be of the
 same
 class.
 
 
 Master File Directives include $ORIGIN, $INCLUDE,
 and $TTL.
 
 <div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="atsign"></a>The @ (at-sign)</h4></div></div></div>

When used in the label (or name) field, the asperand or
 at-sign (@) symbol represents the current origin.
 At the start of the zone file, it is the
 &lt;<code class="varname">zone_name</code>&gt; (followed by
 trailing dot).
 
 </div>
 <div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="origin_directive"></a>The $ORIGIN Directive</h4></div></div></div>

Syntax: $ORIGIN
 <code>domain-name</code>
 [<code>comment</code>]
 
 $ORIGIN
 sets the domain name that will be appended to any
 unqualified records. When a zone is first read in there
 is an implicit $ORIGIN
 &lt;<code class="varname">zone_name</code>&gt;.
 (followed by trailing dot).
 The current $ORIGIN is appended to
 the domain specified in the $ORIGIN
 argument if it is not absolute.

<pre class="programlisting">
$ORIGIN example.com.
WWW CNAME MAIN-SERVER
</pre>

is equivalent to

<pre class="programlisting">
WWW.EXAMPLE.COM. CNAME MAIN-SERVER.EXAMPLE.COM.
</pre>

</div>
 <div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="include_directive"></a>The $INCLUDE Directive</h4></div></div></div>

Syntax: $INCLUDE
 <code>filename</code>
 [
<code>origin</code> ]
 [ <code>comment</code> ]
 
 
 Read and process the file <code class="filename">filename</code> as
 if it were included into the file at this point. If origin is
 specified the file is processed with $ORIGIN set
 to that value, otherwise the current $ORIGIN is
 used.
 
 
 The origin and the current domain name
 revert to the values they had prior to the $INCLUDE once
 the file has been read.
 
 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 
 RFC 1035 specifies that the current origin should be restored
 after
 an $INCLUDE, but it is silent
 on whether the current
 domain name should also be restored. BIND 9 restores both of
 them.
 This could be construed as a deviation from RFC 1035, a
 feature, or both.
 
 </div>
 </div>
 <div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="ttl_directive"></a>The $TTL Directive</h4></div></div></div>

Syntax: $TTL
 <code>default-ttl</code>
 [
<code>comment</code> ]
 
 
 Set the default Time To Live (TTL) for subsequent records
 with undefined TTLs. Valid TTLs are of the range 0-2147483647
 seconds.
 
 $TTL
 is defined in RFC 2308.
 
 </div>
 </div>
 <div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="generate_directive"></a><acronym class="acronym">BIND</acronym> Master File Extension: the $GENERATE Directive</h3></div></div></div>

Syntax: $GENERATE
 <code>range</code>
 <code>lhs</code>
 [<code>ttl</code>]
 [<code>class</code>]
 <code>type</code>
 <code>rhs</code>
 [<code>comment</code>]
 
 $GENERATE
 is used to create a series of resource records that only
 differ from each other by an
 iterator. $GENERATE can be used to
 easily generate the sets of records required to support
 sub /24 reverse delegations described in RFC 2317:
 Classless IN-ADDR.ARPA delegation.

<pre class="programlisting">$ORIGIN 0.0.192.IN-ADDR.ARPA.
$GENERATE 1-2 @ NS SERVER$.EXAMPLE.
$GENERATE 1-127 $ CNAME $.0</pre>

is equivalent to

<pre class="programlisting">0.0.0.192.IN-ADDR.ARPA. NS SERVER1.EXAMPLE.
0.0.0.192.IN-ADDR.ARPA. NS SERVER2.EXAMPLE.
1.0.0.192.IN-ADDR.ARPA. CNAME 1.0.0.0.192.IN-ADDR.ARPA.
2.0.0.192.IN-ADDR.ARPA. CNAME 2.0.0.0.192.IN-ADDR.ARPA.
...
127.0.0.192.IN-ADDR.ARPA. CNAME 127.0.0.0.192.IN-ADDR.ARPA.
</pre>

Generate a set of A and MX records. Note the MX's right hand
 side is a quoted string. The quotes will be stripped when the
 right hand side is processed.

<pre class="programlisting">
$ORIGIN EXAMPLE.
$GENERATE 1-127 HOST-$ A 1.2.3.$
$GENERATE 1-127 HOST-$ MX "0 ."</pre>

is equivalent to

<pre class="programlisting">HOST-1.EXAMPLE. A 1.2.3.1
HOST-1.EXAMPLE. MX 0 .
HOST-2.EXAMPLE. A 1.2.3.2
HOST-2.EXAMPLE. MX 0 .
HOST-3.EXAMPLE. A 1.2.3.3
HOST-3.EXAMPLE. MX 0 .
...
HOST-127.EXAMPLE. A 1.2.3.127
HOST-127.EXAMPLE. MX 0 .
</pre>

<div class="informaltable">
 <table border="1">
<colgroup>
<col width="0.875in" class="1">
<col width="4.250in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 range
 </td>
<td>
 
 This can be one of two forms: start-stop
 or start-stop/step. If the first form is used, then step
 is set to 1. start, stop and step must be positive
 integers between 0 and (2^31)-1. start must not be
 larger than stop.
 
 </td>
</tr>
<tr>
<td>
 lhs
 </td>
<td>
 This
 describes the owner name of the resource records
 to be created. Any single $
 (dollar sign)
 symbols within the lhs string
 are replaced by the iterator value.

To get a $ in the output, you need to escape the
 $ using a backslash
 \,
 e.g. \$. The
 $ may optionally be followed
 by modifiers which change the offset from the
 iterator, field width and base.

Modifiers are introduced by a
 { (left brace) immediately following the
 $ as
 ${offset[,width[,base]]}.
 For example, ${-20,3,d}
 subtracts 20 from the current value, prints the
 result as a decimal in a zero-padded field of
 width 3.

Available output forms are decimal
 (d), octal
 (o), hexadecimal
 (x or X
 for uppercase) and nibble
 (n or N\
 for uppercase). The default modifier is
 ${0,0,d}. If the
 lhs is not absolute, the
 current $ORIGIN is appended
 to the name.
 
 
 In nibble mode the value will be treated as
 if it was a reversed hexadecimal string
 with each hexadecimal digit as a separate
 label. The width field includes the label
 separator.
 
 
 For compatibility with earlier versions,
 $$ is still recognized as
 indicating a literal $ in the output.
 
 </td>
</tr>
<tr>
<td>
 ttl
 </td>
<td>
 
 Specifies the time-to-live of the generated records. If
 not specified this will be inherited using the
 normal TTL inheritance rules.
 
 class
 and ttl can be
 entered in either order.
 
 </td>
</tr>
<tr>
<td>
 class
 </td>
<td>
 
 Specifies the class of the generated records.
 This must match the zone class if it is
 specified.
 
 class
 and ttl can be
 entered in either order.
 
 </td>
</tr>
<tr>
<td>
 type
 </td>
<td>
 
 Any valid type.
 
 </td>
</tr>
<tr>
<td>
 rhs
 </td>
<td>
 
 rhs, optionally, quoted string.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 
 The $GENERATE directive is a <acronym class="acronym">BIND</acronym> extension
 and not part of the standard zone file format.
 
 
 BIND 8 did not support the optional TTL and CLASS fields.
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="zonefile_format"></a>Additional File Formats</h3></div></div></div>

In addition to the standard textual format, BIND 9
 supports the ability to read or dump to zone files in
 other formats.
 
 
 The <code class="constant">raw</code> format is
 a binary representation of zone data in a manner similar
 to that used in zone transfers. Since it does not require
 parsing text, load time is significantly reduced.
 
 
 An even faster alternative is the <code class="constant">map</code>
 format, which is an image of a <acronym class="acronym">BIND</acronym> 9
 in-memory zone database; it is capable of being loaded
 directly into memory via the mmap()
 function; the zone can begin serving queries almost
 immediately.
 
 
 For a primary server, a zone file in
 <code class="constant">raw</code> or <code class="constant">map</code>
 format is expected to be generated from a textual zone
 file by the named-compilezone command.
 For a secondary server or for a dynamic zone, it is automatically
 generated (if this format is specified by the
 masterfile-format option) when
 named dumps the zone contents after
 zone transfer or when applying prior updates.
 
 
 If a zone file in a binary format needs manual modification,
 it first must be converted to a textual form by the
 named-compilezone command. All
 necessary modification should go to the text file, which
 should then be converted to the binary form by the
 named-compilezone command again.
 
 
 Note that map format is extremely
 architecture-specific. A <code class="constant">map</code>
 file cannot be used on a system
 with different pointer size, endianness or data alignment
 than the system on which it was generated, and should in
 general be used only inside a single system.
 While <code class="constant">raw</code> format uses
 network byte order and avoids architecture-dependent
 data alignment so that it is as portable as
 possible, it is also primarily expected to be used
 inside the same single system. To export a
 zone file in either <code class="constant">raw</code> or
 <code class="constant">map</code> format, or make a
 portable backup of such a file, conversion to
 <code class="constant">text</code> format is recommended.
 
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="statistics"></a>BIND9 Statistics</h2></div></div></div>

<acronym class="acronym">BIND</acronym> 9 maintains lots of statistics
 information and provides several interfaces for users to
 get access to the statistics.
 The available statistics include all statistics counters
 that were available in <acronym class="acronym">BIND</acronym> 8 and
 are meaningful in <acronym class="acronym">BIND</acronym> 9,
 and other information that is considered useful.

The statistics information is categorized into the following
 sections.

<div class="informaltable">
 <table border="1">
<colgroup>
<col width="3.300in" class="1">
<col width="2.625in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 Incoming Requests
 </td>
<td>
 
 The number of incoming DNS requests for each OPCODE.
 
 </td>
</tr>
<tr>
<td>
 Incoming Queries
 </td>
<td>
 
 The number of incoming queries for each RR type.
 
 </td>
</tr>
<tr>
<td>
 Outgoing Queries
 </td>
<td>
 
 The number of outgoing queries for each RR
 type sent from the internal resolver.
 Maintained per view.
 
 </td>
</tr>
<tr>
<td>
 Name Server Statistics
 </td>
<td>
 
 Statistics counters about incoming request processing.
 
 </td>
</tr>
<tr>
<td>
 Zone Maintenance Statistics
 </td>
<td>
 
 Statistics counters regarding zone maintenance
 operations such as zone transfers.
 
 </td>
</tr>
<tr>
<td>
 Resolver Statistics
 </td>
<td>
 
 Statistics counters about name resolution
 performed in the internal resolver.
 Maintained per view.
 
 </td>
</tr>
<tr>
<td>
 Cache DB RRsets
 </td>
<td>
 
 The number of RRsets per RR type and nonexistent
 names stored in the cache database.
 If the exclamation mark (!) is printed for a RR
 type, it means that particular type of RRset is
 known to be nonexistent (this is also known as
 "NXRRSET"). If a hash mark (#) is present then
 the RRset is marked for garbage collection.
 Maintained per view.
 
 </td>
</tr>
<tr>
<td>
 Socket I/O Statistics
 </td>
<td>
 
 Statistics counters about network related events.
 
 </td>
</tr>
</tbody>
</table>
 </div>

A subset of Name Server Statistics is collected and shown
 per zone for which the server has the authority when
 zone-statistics is set to
 <code>full</code> (or <code>yes</code>
 for backward compatibility. See the description of
 zone-statistics in <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called &#8220;options Statement Definition and
 Usage&#8221;</a>
 for further details.

These statistics counters are shown with their zone and
 view names. The view name is omitted when the server is
 not configured with explicit views.

There are currently two user interfaces to get access to the
 statistics.
 One is in the plain text format dumped to the file specified
 by the statistics-file configuration option.
 The other is remotely accessible via a statistics channel
 when the statistics-channels statement
 is specified in the configuration file
 (see <a class="xref" href="Bv9ARM.ch06.html#statschannels" title="statistics-channels Statement Grammar">the section called &#8220;statistics-channels Statement Grammar&#8221;</a>.)

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="statsfile"></a>The Statistics File</h3></div></div></div>

The text format statistics dump begins with a line, like:
 
 
 +++ Statistics Dump +++ (973798949)
 
 
 The number in parentheses is a standard
 Unix-style timestamp, measured as seconds since January 1, 1970.

Following
 that line is a set of statistics information, which is categorized
 as described above.
 Each section begins with a line, like:

++ Name Server Statistics ++

Each section consists of lines, each containing the statistics
 counter value followed by its textual description.
 See below for available counters.
 For brevity, counters that have a value of 0 are not shown
 in the statistics file.

The statistics dump ends with the line where the
 number is identical to the number in the beginning line; for example:
 
 
 --- Statistics Dump --- (973798949)
 
 </div>

<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="statistics_counters"></a>Statistics Counters</h3></div></div></div>

The following tables summarize statistics counters that
 <acronym class="acronym">BIND</acronym> 9 provides.
 For each row of the tables, the leftmost column is the
 abbreviated symbol name of that counter.
 These symbols are shown in the statistics information
 accessed via an HTTP statistics channel.
 The rightmost column gives the description of the counter,
 which is also shown in the statistics file
 (but, in this document, possibly with slight modification
 for better readability).
 Additional notes may also be provided in this column.
 When a middle column exists between these two columns,
 it gives the corresponding counter name of the
 <acronym class="acronym">BIND</acronym> 8 statistics, if applicable.

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="stats_counters"></a>Name Server Statistics Counters</h4></div></div></div>

<div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.150in" class="1">
<col width="1.150in" class="2">
<col width="3.350in" class="3">
</colgroup>
<tbody>
<tr>
<td>
 
 Symbol
 
 </td>
<td>
 
 BIND8 Symbol
 
 </td>
<td>
 
 Description
 
 </td>
</tr>
<tr>
<td>
 Requestv4
 </td>
<td>
 RQ
 </td>
<td>
 
 IPv4 requests received.
 Note: this also counts non query requests.
 
 </td>
</tr>
<tr>
<td>
 Requestv6
 </td>
<td>
 RQ
 </td>
<td>
 
 IPv6 requests received.
 Note: this also counts non query requests.
 
 </td>
</tr>
<tr>
<td>
 ReqEdns0
 </td>
<td>
 
 </td>
<td>
 
 Requests with EDNS(0) received.
 
 </td>
</tr>
<tr>
<td>
 ReqBadEDNSVer
 </td>
<td>
 
 </td>
<td>
 
 Requests with unsupported EDNS version received.
 
 </td>
</tr>
<tr>
<td>
 ReqTSIG
 </td>
<td>
 
 </td>
<td>
 
 Requests with TSIG received.
 
 </td>
</tr>
<tr>
<td>
 ReqSIG0
 </td>
<td>
 
 </td>
<td>
 
 Requests with SIG(0) received.
 
 </td>
</tr>
<tr>
<td>
 ReqBadSIG
 </td>
<td>
 
 </td>
<td>
 
 Requests with invalid (TSIG or SIG(0)) signature.
 
 </td>
</tr>
<tr>
<td>
 ReqTCP
 </td>
<td>
 RTCP
 </td>
<td>
 
 TCP requests received.
 
 </td>
</tr>
<tr>
<td>
 AuthQryRej
 </td>
<td>
 RUQ
 </td>
<td>
 
 Authoritative (non recursive) queries rejected.
 
 </td>
</tr>
<tr>
<td>
 RecQryRej
 </td>
<td>
 RURQ
 </td>
<td>
 
 Recursive queries rejected.
 
 </td>
</tr>
<tr>
<td>
 XfrRej
 </td>
<td>
 RUXFR
 </td>
<td>
 
 Zone transfer requests rejected.
 
 </td>
</tr>
<tr>
<td>
 UpdateRej
 </td>
<td>
 RUUpd
 </td>
<td>
 
 Dynamic update requests rejected.
 
 </td>
</tr>
<tr>
<td>
 Response
 </td>
<td>
 SAns
 </td>
<td>
 
 Responses sent.
 
 </td>
</tr>
<tr>
<td>
 RespTruncated
 </td>
<td>
 
 </td>
<td>
 
 Truncated responses sent.
 
 </td>
</tr>
<tr>
<td>
 RespEDNS0
 </td>
<td>
 
 </td>
<td>
 
 Responses with EDNS(0) sent.
 
 </td>
</tr>
<tr>
<td>
 RespTSIG
 </td>
<td>
 
 </td>
<td>
 
 Responses with TSIG sent.
 
 </td>
</tr>
<tr>
<td>
 RespSIG0
 </td>
<td>
 
 </td>
<td>
 
 Responses with SIG(0) sent.
 
 </td>
</tr>
<tr>
<td>
 QrySuccess
 </td>
<td>
 
 </td>
<td>
 
 Queries resulted in a successful answer.
 This means the query which returns a NOERROR response
 with at least one answer RR.
 This corresponds to the
 success counter
 of previous versions of
 <acronym class="acronym">BIND</acronym> 9.
 
 </td>
</tr>
<tr>
<td>
 QryAuthAns
 </td>
<td>
 
 </td>
<td>
 
 Queries resulted in authoritative answer.
 
 </td>
</tr>
<tr>
<td>
 QryNoauthAns
 </td>
<td>
 SNaAns
 </td>
<td>
 
 Queries resulted in non authoritative answer.
 
 </td>
</tr>
<tr>
<td>
 QryReferral
 </td>
<td>
 
 </td>
<td>
 
 Queries resulted in referral answer.
 This corresponds to the
 referral counter
 of previous versions of
 <acronym class="acronym">BIND</acronym> 9.
 
 </td>
</tr>
<tr>
<td>
 QryNxrrset
 </td>
<td>
 
 </td>
<td>
 
 Queries resulted in NOERROR responses with no data.
 This corresponds to the
 nxrrset counter
 of previous versions of
 <acronym class="acronym">BIND</acronym> 9.
 
 </td>
</tr>
<tr>
<td>
 QrySERVFAIL
 </td>
<td>
 SFail
 </td>
<td>
 
 Queries resulted in SERVFAIL.
 
 </td>
</tr>
<tr>
<td>
 QryFORMERR
 </td>
<td>
 SFErr
 </td>
<td>
 
 Queries resulted in FORMERR.
 
 </td>
</tr>
<tr>
<td>
 QryNXDOMAIN
 </td>
<td>
 SNXD
 </td>
<td>
 
 Queries resulted in NXDOMAIN.
 This corresponds to the
 nxdomain counter
 of previous versions of
 <acronym class="acronym">BIND</acronym> 9.
 
 </td>
</tr>
<tr>
<td>
 QryRecursion
 </td>
<td>
 RFwdQ
 </td>
<td>
 
 Queries which caused the server
 to perform recursion in order to find the final answer.
 This corresponds to the
 recursion counter
 of previous versions of
 <acronym class="acronym">BIND</acronym> 9.
 
 </td>
</tr>
<tr>
<td>
 QryDuplicate
 </td>
<td>
 RDupQ
 </td>
<td>
 
 Queries which the server attempted to
 recurse but discovered an existing query with the same
 IP address, port, query ID, name, type and class
 already being processed.
 This corresponds to the
 duplicate counter
 of previous versions of
 <acronym class="acronym">BIND</acronym> 9.
 
 </td>
</tr>
<tr>
<td>
 QryDropped
 </td>
<td>
 
 </td>
<td>
 
 Recursive queries for which the server
 discovered an excessive number of existing
 recursive queries for the same name, type and
 class and were subsequently dropped.
 This is the number of dropped queries due to
 the reason explained with the
 clients-per-query
 and
 max-clients-per-query
 options
 (see the description about
 <a class="xref" href="Bv9ARM.ch06.html#clients-per-query">clients-per-query</a>.)
 This corresponds to the
 dropped counter
 of previous versions of
 <acronym class="acronym">BIND</acronym> 9.
 
 </td>
</tr>
<tr>
<td>
 QryFailure
 </td>
<td>
 
 </td>
<td>
 
 Other query failures.
 This corresponds to the
 failure counter
 of previous versions of
 <acronym class="acronym">BIND</acronym> 9.
 Note: this counter is provided mainly for
 backward compatibility with the previous versions.
 Normally a more fine-grained counters such as
 AuthQryRej and
 RecQryRej
 that would also fall into this counter are provided,
 and so this counter would not be of much
 interest in practice.
 
 </td>
</tr>
<tr>
<td>
 QryNXRedir
 </td>
<td>
 
 </td>
<td>
 
 Queries resulted in NXDOMAIN that were redirected.
 
 </td>
</tr>
<tr>
<td>
 QryNXRedirRLookup
 </td>
<td>
 
 </td>
<td>
 
 Queries resulted in NXDOMAIN that were redirected
 and resulted in a successful remote lookup.
 
 </td>
</tr>
<tr>
<td>
 XfrReqDone
 </td>
<td>
 
 </td>
<td>
 
 Requested zone transfers completed.
 
 </td>
</tr>
<tr>
<td>
 UpdateReqFwd
 </td>
<td>
 
 </td>
<td>
 
 Update requests forwarded.
 
 </td>
</tr>
<tr>
<td>
 UpdateRespFwd
 </td>
<td>
 
 </td>
<td>
 
 Update responses forwarded.
 
 </td>
</tr>
<tr>
<td>
 UpdateFwdFail
 </td>
<td>
 
 </td>
<td>
 
 Dynamic update forward failed.
 
 </td>
</tr>
<tr>
<td>
 UpdateDone
 </td>
<td>
 
 </td>
<td>
 
 Dynamic updates completed.
 
 </td>
</tr>
<tr>
<td>
 UpdateFail
 </td>
<td>
 
 </td>
<td>
 
 Dynamic updates failed.
 
 </td>
</tr>
<tr>
<td>
 UpdateBadPrereq
 </td>
<td>
 
 </td>
<td>
 
 Dynamic updates rejected due to prerequisite failure.
 
 </td>
</tr>
<tr>
<td>
 RateDropped
 </td>
<td>
 
 </td>
<td>
 
 Responses dropped by rate limits.
 
 </td>
</tr>
<tr>
<td>
 RateSlipped
 </td>
<td>
 
 </td>
<td>
 
 Responses truncated by rate limits.
 
 </td>
</tr>
<tr>
<td>
 RPZRewrites
 </td>
<td>
 
 </td>
<td>
 
 Response policy zone rewrites.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="zone_stats"></a>Zone Maintenance Statistics Counters</h4></div></div></div>

<div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.150in" class="1">
<col width="3.350in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 
 Symbol
 
 </td>
<td>
 
 Description
 
 </td>
</tr>
<tr>
<td>
 NotifyOutv4
 </td>
<td>
 
 IPv4 notifies sent.
 
 </td>
</tr>
<tr>
<td>
 NotifyOutv6
 </td>
<td>
 
 IPv6 notifies sent.
 
 </td>
</tr>
<tr>
<td>
 NotifyInv4
 </td>
<td>
 
 IPv4 notifies received.
 
 </td>
</tr>
<tr>
<td>
 NotifyInv6
 </td>
<td>
 
 IPv6 notifies received.
 
 </td>
</tr>
<tr>
<td>
 NotifyRej
 </td>
<td>
 
 Incoming notifies rejected.
 
 </td>
</tr>
<tr>
<td>
 SOAOutv4
 </td>
<td>
 
 IPv4 SOA queries sent.
 
 </td>
</tr>
<tr>
<td>
 SOAOutv6
 </td>
<td>
 
 IPv6 SOA queries sent.
 
 </td>
</tr>
<tr>
<td>
 AXFRReqv4
 </td>
<td>
 
 IPv4 AXFR requested.
 
 </td>
</tr>
<tr>
<td>
 AXFRReqv6
 </td>
<td>
 
 IPv6 AXFR requested.
 
 </td>
</tr>
<tr>
<td>
 IXFRReqv4
 </td>
<td>
 
 IPv4 IXFR requested.
 
 </td>
</tr>
<tr>
<td>
 IXFRReqv6
 </td>
<td>
 
 IPv6 IXFR requested.
 
 </td>
</tr>
<tr>
<td>
 XfrSuccess
 </td>
<td>
 
 Zone transfer requests succeeded.
 
 </td>
</tr>
<tr>
<td>
 XfrFail
 </td>
<td>
 
 Zone transfer requests failed.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="resolver_stats"></a>Resolver Statistics Counters</h4></div></div></div>

</div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="socket_stats"></a>Socket I/O Statistics Counters</h4></div></div></div>

Socket I/O statistics counters are defined per socket
 types, which are
 UDP4 (UDP/IPv4),
 UDP6 (UDP/IPv6),
 TCP4 (TCP/IPv4),
 TCP6 (TCP/IPv6),
 Unix (Unix Domain), and
 FDwatch (sockets opened outside the
 socket module).
 In the following table &lt;TYPE&gt;
 represents a socket type.
 Not all counters are available for all socket types;
 exceptions are noted in the description field.

<div class="informaltable">
 <table border="1">
<colgroup>
<col width="1.150in" class="1">
<col width="3.350in" class="2">
</colgroup>
<tbody>
<tr>
<td>
 
 Symbol
 
 </td>
<td>
 
 Description
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;Open
 </td>
<td>
 
 Sockets opened successfully.
 This counter is not applicable to the
 FDwatch type.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;OpenFail
 </td>
<td>
 
 Failures of opening sockets.
 This counter is not applicable to the
 FDwatch type.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;Close
 </td>
<td>
 
 Sockets closed.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;BindFail
 </td>
<td>
 
 Failures of binding sockets.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;ConnFail
 </td>
<td>
 
 Failures of connecting sockets.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;Conn
 </td>
<td>
 
 Connections established successfully.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;AcceptFail
 </td>
<td>
 
 Failures of accepting incoming connection requests.
 This counter is not applicable to the
 UDP and
 FDwatch types.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;Accept
 </td>
<td>
 
 Incoming connections successfully accepted.
 This counter is not applicable to the
 UDP and
 FDwatch types.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;SendErr
 </td>
<td>
 
 Errors in socket send operations.
 This counter corresponds
 to SErr counter of
 BIND 8.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;RecvErr
 </td>
<td>
 
 Errors in socket receive operations.
 This includes errors of send operations on a
 connected UDP socket notified by an ICMP error
 message.
 
 </td>
</tr>
</tbody>
</table>
 </div>
 </div>

<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="bind8_compatibility"></a>Compatibility with BIND 8 Counters</h4></div></div></div>

Most statistics counters that were available
 in BIND 8 are also supported in
 BIND 9 as shown in the above tables.
 Here are notes about other counters that do not appear
 in these tables.

<div class="variablelist"><dl class="variablelist">
<dt>RFwdR,SFwdR</dt>
<dd>
 
 These counters are not supported
 because BIND 9 does not adopt
 the notion of forwarding
 as BIND 8 did.
 
 </dd>
<dt>RAXFR</dt>
<dd>
 
 This counter is accessible in the Incoming Queries section.
 
 </dd>
<dt>RIQ</dt>
<dd>
 
 This counter is accessible in the Incoming Requests section.
 
 </dd>
<dt>ROpts</dt>
<dd>
 
 This counter is not supported
 because BIND 9 does not care
 about IP options in the first place.
 
 </dd>
</dl></div>
 </div>
 </div>
 </div>

</div>
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<td width="40%" align="left" valign="top">Chapter 5. The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver </td>
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BIND 9.11.4-P2 (Extended Support Version)
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