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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> Primary 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">BIND 9 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>
<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 class="informaltable" 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_list</code>s.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">domain_name</code>
 
 </td>
<td>
 
 A quoted string which is 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 a
 delimiter. It is strongly recommended to use
 string zone names rather than numeric identifiers,
 to be robust against system configuration
 changes. However, since there is no standard
 mapping for such names and identifier values,
 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 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 an <code class="varname">ip_addr</code>
 may be 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
 matches 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
 contexts in which they are used.
 
 </td>
</tr>
<tr>
<td>
 
 <code class="varname">path_name</code>
 
 </td>
<td>
 
 A quoted string which is 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>
 
 A <code class="varname">size_spec</code> or integer value
 followed by "%" to represent percent.
 
 
 The behavior is exactly the same as
 <code class="varname">size_spec</code>, but
 <code class="varname">size_or_percent</code> also allows
 specifying a positive integer value followed by the
 "%"" sign to represent percent.
 
 </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 secondary 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-1.7.2.4.2"></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-1.7.2.4.3"></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 causes 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 is 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 matches 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 blocking 1.2.3.13 via the negation, but
 all other 1.2.3.* hosts pass 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
 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-1.7.2.5.3"></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-1.7.2.5.4"></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) 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>

 The semicolon (";") character
 cannot start a comment, unlike 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 class="informaltable" 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 information the server logs and where
 the log messages are sent.
 
 </td>
</tr>
<tr>
<td>
 lwres
 </td>
<td>
 
 Configures named to
 also act as a lightweight resolver daemon (lwresd).
 
 </td>
</tr>
<tr>
<td>
 masters
 </td>
<td>
 
 Defines a named list of primary servers for
 inclusion in stub and secondary 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 one of the primary
 uses of address match lists: Access Control Lists (ACLs).
 

 The following ACLs are built-in:
 
<div class="informaltable"><table class="informaltable" 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 cases, 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 manage 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 are
 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 rndc is only used 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 sets 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 attempts 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 when <acronym class="acronym">BIND</acronym> was built).
 To create an <code class="filename">rndc.key</code> file, run
 <code>rndc-confgen -a</code>.
 

 The key name and the size of the secret cannot be easily changed; if it
 is desirable to change those things, make a
 <code class="filename">rndc.conf</code> with a custom key. 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.
 For greater flexibility in allowing other users to access
 rndc commands, 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 that uniquely identifies 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 desired. If there is no logging statement,
 the logging configuration is:
 
<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 is:
 
<pre class="programlisting">logging {
 category default { default_logfile; default_debug; };
 category unmatched { null; };
};
</pre>

 The logging configuration
 is only established when
 the entire configuration file has been parsed. When the server starts 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;
 there is no limit to the number of channels that can be created.
 

 Every channel definition must include a destination clause that
 says whether messages selected for the channel go to a file, go to a
 particular syslog facility, go to the standard error stream, or are
 discarded. The definition can optionally also limit the message severity level
 that is accepted by the channel (the default is
 info), and whether to include a
 named-generated time stamp, the
 category name,
 and/or the 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 on how many
 versions
 of the file are saved each time the file is opened.
 

 If the versions log file
 option is used, then
 named retains that many backup
 versions of the file by
 renaming them when opening. For example, to keep
 three old versions
 of the file <code class="filename">lamers.log</code>, 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>.
 The versions unlimited option can be set 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
 stops writing to the file unless it also 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 is
 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.
 

 Here is an example using 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 handles messages
 sent to
 this facility is described in the syslog.conf man
 page. On a system which uses a very old version of syslog, which
 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 when writing
 straight to a file rather than using syslog.
 Messages which are not at least of the severity level given are
 not selected for the channel; messages of higher severity
 levels
 are accepted.
 

 When using syslog, the syslog.conf priorities
 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,
 causes 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, as
 when debugging a configuration, for example.
 

 The server can supply extensive debugging information when
 it is in debugging mode. If the server's global debug level is
 greater
 than zero, debugging mode is 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; 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>

 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 is set to
 <code>yes</code>, then the date and time are logged.
 print-time may be specified for a
 syslog channel, but is usually
 unnecessary since syslog also logs
 the date and time. If print-category is
 set to <code>yes</code>, then the
 category of the message is logged as well. Finally, if
 print-severity is set, then the severity
 level of the message is logged.
 The print- options may
 be used in any combination, and are always 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 is not 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
 non-zero. 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 - and still running as root - is discarded.
 To capture this output, 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 can be redirected to a file.
 

 Once a channel is defined, it cannot be redefined.
 The built-in channels cannot be altered directly, but
 the default logging can be modified by pointing categories at defined channels.
 
</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 desired logs
 can be sent anywhere while unwanted logs are ignored. If
 a list of channels is not specified for a category, log
 messages
 in that category are sent to the default category
 instead. If no default category is specified, the following
 "default default" is used:
 
<pre class="programlisting">category default { default_syslog; default_debug; };
</pre>

 If named is started with the
 <code class="option">-L</code> option, the default category is:
 
<pre class="programlisting">category default { default_logfile; default_debug; };
</pre>

 As an example, let's say a user wants to log security events to
 a file, but also wants to keep the default logging behavior. They would
 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>

 The 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 class="informaltable" 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>
	 
	 Name servers that are skipped for 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>
	 
	 Logging
	 options for those categories where no specific
	 configuration has been
	 defined.
	 
	</td>
</tr>
<tr>
<td>
	 delegation-only
	</td>
<td>
	 
	 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
	 DNSSEC validation, which requires EDNS for
	 the DNSSEC records to be returned.
	 
	</td>
</tr>
<tr>
<td>
	 general
	</td>
<td>
	 
	 Catch-all for many things that still are not
	 classified into categories.
	 
	</td>
</tr>
<tr>
<td>
	 lame-servers
	</td>
<td>
	 
	 Misconfigurations
	 in remote servers, discovered by <acronym class="acronym">BIND</acronym> 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>
	 
	 Location where queries should be logged.
	 
	 
	 At startup, specifying the category queries also
	 enables 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), whether the query was signed (S),
	 whether EDNS was in use along with the EDNS version
	 number (E(#)), whether TCP was used (T), whether DO
	 (DNSSEC Ok) was set (D), whether CD (Checking
	 Disabled) was set (C), whether a valid DNS Server
	 COOKIE was received (V), and whether 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 limiting stops.
	 A lack of memory can hurry the final notice,
	 which is indicated by an initial asterisk (*).
	 Various internal events are logged at debug level 1
	 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>
	 
	 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>
	 
	 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
 used to indicate why and how specific queries resulted in
 responses which indicate an error. Normally, these messages
 will be logged at debug logging levels;
 note, however, that if query logging is active, some are
 logged at info. The logging levels are
 described below:
 

 At debug level 1 or higher - or at
 info, when query logging is active - each
 response with response code 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 are particularly helpful in identifying the cause of
 SERVFAIL for an authoritative server.
 

 At debug level 2 or higher, detailed
 context information about recursive resolutions that resulted in
 SERVFAIL is logged. The log message looks like this:

<pre class="programlisting">
fetch completed at resolver.c:2970 for www.example.com/A
in 10.000183: timed out/success [domain:example.com,
referral:2,restart:7,qrysent:8,timeout:5,lame:0,quota: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 10.000183 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 next part shows the detected final result and the
 latest result of DNSSEC validation. The latter is always
 "success" when no validation attempt was made. In this example,
 this query probably resulted in SERVFAIL because all name
 servers are down or unreachable, leading to a timeout in 10
 seconds. DNSSEC validation was probably not attempted.
 

 The last part, enclosed in square brackets, shows statistics
 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 class="informaltable" 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 there are two, 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
 BIND 9's address database (ADB), where lame
 servers are cached.
 
 </td>
</tr>
<tr>
<td>
 <code class="varname">quota</code>
 </td>
<td>
 
 The number of times the resolver was unable
 to send a query because it had exceeded the
 permissible fetch quota for a server.
 
 </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 when 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 to resolve 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 debug level 3 or higher, the same
 messages as those at debug level 1 are
 logged for errors other than SERVFAIL. Note that negative
 responses such as NXDOMAIN are not errors, and are not logged
 at this debug level.
 

 At debug level 4 or higher, the
 detailed context information logged at debug
 level 2 is logged for errors other than SERVFAIL and
 for negative responses such as NXDOMAIN.
 
</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 are 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 is constructed in the same manner as a normal DNS
 query
 matching this view. If this statement is omitted, the default view
 is
 used; 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 dedicates 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> statement 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 are silently ignored and
 the maximum is 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 primaries to be easily used by
 multiple stub and secondary 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>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 | siphash24 );
	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>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 is
 used.
 
<div class="variablelist"><dl class="variablelist">
<dt>attach-cache</dt>
<dd>

 This option 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 simply refer to the
 already-created cache.
 

 One common configuration to share a cache is to
 allow all views to share a single cache.
 This can be done by specifying
 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
 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 of 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 that
 configuration differences in different views do
 not cause disruption with a shared cache.
 
</dd>
<dt>directory</dt>
<dd>
 This sets the working directory of the server.
 Any non-absolute pathnames in the configuration file are
 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 <acronym class="acronym">BIND</acronym> 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> causes 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:
 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>

 This configures the path to which the dnstap
 frame stream is 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 are
 only 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>
 This 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 is sent. If set to
 <code class="literal">none</code>, no identity string is sent.
 </dd>
<dt>dnstap-version</dt>
<dd>
 This specifies a version string to send in
 dnstap messages. The default is the
 version number of the <acronym class="acronym">BIND</acronym> release. If set to
 <code class="literal">none</code>, no version string is sent.
 </dd>
<dt>geoip-directory</dt>
<dd>
 When named is compiled using the
 MaxMind GeoIP2 geolocation API, or the legacy GeoIP API,
 this specifies the directory containing GeoIP
 database files. By default, the option is set based on
 the prefix used to build the libmaxminddb
 module; for example, if the library is installed in
 <code class="filename">/usr/local/lib</code>, then the default
 geoip-directory is
 <code class="filename">/usr/local/share/GeoIP</code>. On Windows,
 the default is the named working
 directory. 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> for details about
 geoip ACLs.
 </dd>
<dt>key-directory</dt>
<dd>
 This is the
 directory where the public and private DNSSEC key files
 should be found when performing a dynamic update of secure zones, 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>

 This 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,
 managed keys for the server are tracked in a single
 file called <code class="filename">managed-keys.bind</code>.
 Otherwise, managed keys are tracked in separate files,
 one file per view; each file name is 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 earlier releases, file names for views
 always used the SHA256 hash of the view name. To ensure
 compatibility after upgrading, if a file using the old
 name format is found to exist, it is used instead
 of the new format.)
 
</dd>
<dt>named-xfer</dt>
<dd>
 This option is obsolete.
 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>
 This is the KRB5 keytab file to use for GSS-TSIG updates. If
 this option is set and tkey-gssapi-credential is not
 set, updates are allowed with any key
 matching a principal in the specified keytab.
 </dd>
<dt>tkey-gssapi-credential</dt>
<dd>
 This is the security credential with which the server should
 authenticate keys requested by the GSS-TSIG protocol.
 Currently only Kerberos 5 authentication is available;
 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 of the 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>
 This domain is 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 is
 <code class="varname">client-specified part</code> +
 <code class="varname">tkey-domain</code>. Otherwise, the
 name of the shared key is <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
 nonexistent subdomain like
 "_tkey.<code class="varname">domainname</code>". If
 using GSS-TSIG, this variable must be defined, unless
 a specific keytab is specified using tkey-gssapi-keytab.
 </dd>
<dt>tkey-dhkey</dt>
<dd>
 This is 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>
 This is 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>
 This is 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>

 This is the pathname of a file on which named
 attempts to acquire a file lock when starting for
 the first time; if unsuccessful, the server
 terminates, under the assumption that another
 server is already running. If not specified, the default is
 <code class="filename">none</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.
 
</dd>
<dt>pid-file</dt>
<dd>
 This is 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 send signals to
 the running
 name server. Specifying pid-file none disables the
 use of a PID file; no file is written and any
 existing one is removed. Note that none
 is a keyword, not a filename, and therefore is not enclosed
 in
 double quotes.
 </dd>
<dt>recursing-file</dt>
<dd>
 This is the pathname of the file where 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>
 This is 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>
 This is 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>
 This is 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>
 This is 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>
 This is the key name to use for the TSIG session key.
 If not specified, the default is <code class="varname">local-ddns</code>.
 </dd>
<dt>session-keyalg</dt>
<dd>
 This is 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>
 This is the UDP/TCP port number the server uses to
 receive and send DNS protocol traffic.
 The default is 53. This option is mainly intended for server
 testing;
 a server using a port other than 53 is not able to
 communicate with
 the global DNS.
 </dd>
<dt>dscp</dt>
<dd>
 This is 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>
 This specifies a 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 option specifies the device (or file) from which
 to read
 entropy. If it is a file, operations requiring entropy will
 fail when the
 file has been exhausted. If random-device is 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) is 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>

 This turns 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, and the
 authority section is 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 <code class="varname">ANY</code>.
 

 Note that 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>

 This disables the specified DNSSEC algorithms at and below the
 specified name.
 Multiple disable-algorithms
 statements are allowed.
 Only the best-match disable-algorithms
 clause is used to determine the algorithms.
 

 If all supported algorithms are disabled, the zones covered
 by the disable-algorithms setting are treated
 as insecure.
 

 Configured trust anchors in trusted-keys
 or managed-keys that match a disabled
 algorithm are ignored and treated as if they were not
 configured.
 
</dd>
<dt>disable-ds-digests</dt>
<dd>

 This disables the specified DS digest types at and below the
 specified name.
 Multiple disable-ds-digests
 statements are allowed.
 Only the best-match disable-ds-digests
 clause is used to determine the digest types.
 

 If all supported digest types are disabled, the zones covered
 by disable-ds-digests are 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
 is appended to the key name and a DLV record is
 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
 to use ISC DLV with minimal configuration, has
 accordingly been removed.
 
</dd>
<dt>dnssec-must-be-secure</dt>
<dd>
 This specifies hierarchies which must be or may not be secure
 (signed and validated). If <code>yes</code>,
 then named only accepts answers if
 they are secure. If <code>no</code>, then normal
 DNSSEC validation applies, allowing 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, per RFC 6052. Bits 64..71 inclusive must
 be zero, with the most significant bit of the prefix in
 position 0.
 

 In addition, a reverse IP6.ARPA zone is 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
 can be set at the view/options level but not
 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 does not apply to a domain name that
 owns one or more AAAA records; these records are
 simply returned. The optional
 exclude ACL allows specification
 of a list of IPv6 addresses that are ignored
 if they appear in a domain name's AAAA records;
 DNS64 is 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
 only happens for recursive queries. The default
 is no.
 

 If break-dnssec is set to
 yes, the DNS64 synthesis
 happens 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 does 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 automatically signs all new
 or changed records and maintains 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 signs all new or
 changed records, but scheduled maintenance of
 signatures is disabled.
 

 With either of these settings, named
 rejects 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>

 This specifies the default lifetime, in seconds,
 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
 aborts the DNSSEC validation process and treats 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>

 This specifies 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 periodically sends 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>

 This 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> causes 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 is 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 to be used for
 the zone serial number in the SOA record.
 

 With the default setting of
 serial-update-method increment;, the
 SOA serial number is incremented by one each time
 the zone is updated.
 

 When set to
 serial-update-method unixtime;, the
 SOA serial number is 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 is 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 collects
 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
 dumps 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 operating
 system, this automatically rescans network interfaces when the
 interface addresses are added or removed. The default is
 <code>yes</code>. This configuration option does
 not affect the time-based interface-interval
 option; it is recommended to set the time-based
 interface-interval to 0 when the operator
 confirms that automatic interface scanning is supported by the
 operating system.
 

 The automatic-interface-scan implementation
 uses routing sockets for the network interface discovery;
 therefore, the operating system must support the routing
 sockets for this feature to work.
 
</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.
 

 Configurations for zones added at runtime are
 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>.
 </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>
 This writes memory statistics to the file specified by
 memstatistics-file at exit.
 The default is <code>no</code> unless
 <code>-m record</code> 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. Although this setting has different effects
 according
 to zone type, it concentrates the zone maintenance so that
 everything
 happens quickly, once every heartbeat-interval,
 ideally during a single call. It also suppresses some
 normal
 zone maintenance traffic. The default is <code>no</code>.
 

 If specified in the view and
 zone statements, the dialup option
 overrides the global dialup option.
 

 If the zone is a primary zone, the server sends out a
 NOTIFY
 request to all the secondaries (default). This should trigger the
 zone serial
 number check in the secondary (providing it supports NOTIFY),
 allowing the secondary
 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 secondary or stub zone, the server suppresses
 the regular
 "zone up to date" (refresh) queries and only performs 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 disables normal
 refresh
 processing.
 
<div class="informaltable"><table class="informaltable" 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
 did not 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 upon 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.
 It is not implemented in BIND 9.
 </dd>
<dt>root-key-sentinel</dt>
<dd>
 If <code>yes</code>, 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. 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 use 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 only adds 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 omits 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 that handle
 both authoritative and recursive queries.
 

 The default is <code>no</code>.
 
</dd>
<dt>minimal-any</dt>
<dd>
 If set to <code>yes</code>, the server replies with only one
 of the RRsets for the query name, and its covering
 RRSIGs if any, when
 generating a positive response to a query of type
 ANY over UDP, instead of replying with all known
 RRsets for the name. Similarly, a query for type
 RRSIG is 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
 are 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 primary
 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 primary
 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 primary 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 secondary zones
 to crash.
 
</dd>
<dt>notify-to-soa</dt>
<dd>
 If <code>yes</code>, do not check the name servers
 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 primary server.
 Sometimes, however, a secondary server is listed as the SOA MNAME in
 hidden primary configurations; in that case,
 the ultimate primary should be set to still send NOTIFY messages to
 all the name servers listed in the NS RRset.
 </dd>
<dt>recursion</dt>
<dd>
 If <code>yes</code>, and a
 DNS query requests recursion, then the server attempts
 to do
 all the work required to answer the query. If recursion is
 off
 and the server does not already know the answer, it
 returns 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>

 If <code>yes</code>, 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 nonexistent
 server cookie.
 The default is <code>no</code>.
 

 Users wishing to test that DNS COOKIE clients correctly handle BADCOOKIE, or who are
 getting a lot of forged DNS requests with DNS COOKIES
 present, should set this to <code>yes</code>.
 Setting this to <code>yes</code>
 results in a reduced amplification effect in a reflection
 attack, as the BADCOOKIE response is smaller than
 a full response, while also requiring a legitimate client
 to follow up with a second query with the new, valid, cookie.
 
</dd>
<dt>answer-cookie</dt>
<dd>

 When set to the default value of <code>yes</code>,
 COOKIE EDNS options are sent when applicable in
 replies to client queries. If set to
 <code>no</code>, COOKIE EDNS options are not
 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 communicated with 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.
 The default is <code>yes</code>.
 </dd>
<dt>nocookie-udp-size</dt>
<dd>
 This sets the maximum size of UDP responses that are
 sent to queries without a valid server COOKIE. A value
 below 128 is silently raised to 128. The default
 value is 4096, but the max-udp-size
 option may further limit the response size as the default
 for max-udp-size is 1232.
 </dd>
<dt>sit-secret</dt>
<dd>
 This experimental option is obsolete.
 </dd>
<dt>cookie-algorithm</dt>
<dd>
 This sets the algorithm to be used when generating the
 server cookie; the options are "aes", "sha1", or "sha256".
 The default is "aes" if supported by the cryptographic
 library; 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
 generates 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
 are only used to verify returned cookies.
 
</dd>
<dt>rfc2308-type1</dt>
<dd>

 Setting this to <code>yes</code>
 causes 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>

 This is not yet implemented in <acronym class="acronym">BIND</acronym>
 9.
 
</div>
</dd>
<dt>trust-anchor-telemetry</dt>
<dd>

 This 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 are
 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.
 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 is 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 secondary zones may be added and modified by
 untrusted third parties. Also, avoiding
 the search for this additional data speeds 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> are 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 is not able to provide
 upwards
 referrals when additional-from-cache no
 has been specified. Instead, it responds 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 matches 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 causes the response to not verify,
 because the DNSSEC protocol is designed to 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, is 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>
 This is 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 primary zone from its zone file or receives a
 new version of a secondary file via zone transfer, it
 compares the new version to the previous one and calculates
 a set of differences. The differences are then logged in
 the zone's journal file so that the changes can be
 transmitted to downstream secondaries 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
 primary server.
 In particular, if the new version of a zone is completely
 different from the previous one, the set of differences
 is of a size comparable to the combined size of the
 old and new zone versions, and the server needs 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 primary or secondary zones, respectively.
 It is off by default.
 

 Note: if inline signing is enabled for a zone, the
 user-provided ixfr-from-differences
 setting is ignored for that zone.
 
</dd>
<dt>multi-master</dt>
<dd>
 This should be set when there are multiple primary servers for a zone
 and the
 addresses refer to different machines. If <code>yes</code>, named does
 not log
 when the serial number on the primary 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 a 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 is 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 does not return DNSSEC-related
 resource records unless specifically queried for.
 The default is <code>yes</code>.
 </dd>
<dt>dnssec-validation</dt>
<dd>

 This option enables DNSSEC validation in named.
 Note that 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 loads 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 loads only
 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>
 This accepts 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>

 Query logging provides a complete log of all incoming
 queries and all query errors. This provides more insight
 into the server's activity, but with a cost to
 performance which may be significant on heavily loaded
 servers.
 

 The querylog option specifies
 whether query logging should be active when
 named first starts.
 If querylog is not specified, then
 query logging is determined by the presence of the
 logging category queries.
 Query logging can also be activated at runtime using the
 command rndc querylog on, or
 deactivated with rndc querylog off.
 
</dd>
<dt>check-names</dt>
<dd>

 This option is used to restrict the character set and syntax
 of
 certain domain names in zone files and/or DNS responses
 received
 from the network. The default varies according to usage
 area. For primary zones (i.e.,
 type master),
 the default is fail.
 For secondary zones (type slave), 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 further applies to the RDATA of PTR records where the owner
 name indicates 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>
 This checks primary 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>
 This checks 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 primary zones. The default (yes) is to check
 for non-terminal wildcards and issue a warning.
 </dd>
<dt>check-integrity</dt>
<dd>

 This performs post-load zone integrity checks on primary
 zones. It 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 to publish 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; they 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,
 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>
 If <code>yes</code>, 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>
 If <code>yes</code>, when caching a negative response to an 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 is 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) are used
 to sign the DNSKEY RRset at the zone apex. Zone-signing
 keys (keys without the KSK bit set) are 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>
 If <code>yes</code>, try to refresh the zone using TCP if UDP queries fail.
 The default is
 yes.
 </dd>
<dt>dnssec-secure-to-insecure</dt>
<dd>

 This allows 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
 are removed from the zone as well.
 

 If the zone uses NSEC3, it is also necessary to
 delete the NSEC3PARAM RRset from the zone apex; this
 causes 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> is
 the default and causes the server to query the forwarders
 first;
 if that does not answer the question, the server then
 looks for
 the answer itself. If <code class="varname">only</code> is
 specified, the
 server only queries the forwarders.
 </dd>
<dt>forwarders</dt>
<dd>
 This specifies a list of IP addresses to which queries are
 forwarded. The default is the empty list (no forwarding).
 Each address in the list can be associated with an optional
 port number and/or DSCP value, and a default port number and
 DSCP value can be set for the entire list.
 </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. Particular domains can be set 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>
 This 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, the dual-stack-servers parameter has 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>
 This ACL specifies which hosts are allowed to
 notify this secondary server of zone changes in addition
 to the zone primaries.
 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 secondary zone. If not specified, the default is to
 process notify messages
 only from a zone's primary.
 </dd>
<dt>allow-query</dt>
<dd>

 This 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
 used to specify access to the cache.
 
</div>
</dd>
<dt>allow-query-on</dt>
<dd>

 This 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 is 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>
 This specifies which hosts are allowed to get answers
 from the cache. If allow-query-cache
 is not set, BIND checks to see if the following parameters
 are set, in order: allow-recursion and
 allow-query
 (unless recursion no; is
 set, in which case none; is used).
 If neither of those parameters is set, the default (localnets;
 localhost;) is used.
 </dd>
<dt>allow-query-cache-on</dt>
<dd>
 This specifies which local addresses can send 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>
 This specifies which hosts are allowed to make recursive
 queries through this server. BIND checks to see if the
 following parameters are set, in order:
 allow-recursion, allow-query-cache,
 and allow-query.
 If none of those parameters are set, the default
 (localnets;
 localhost;) is used.
 </dd>
<dt>allow-recursion-on</dt>
<dd>
 This 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>
 This specifies which hosts are allowed to
 submit Dynamic DNS updates for primary 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>

 This specifies which hosts are allowed to
 submit Dynamic DNS updates to secondary zones to be forwarded to
 the
 primary. The default is <code>{ none; }</code>,
 which
 means that no update forwarding is 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;
 the responsibility for update access control should rest
 with the
 primary server, not the secondaries.
 

 Note that enabling the update forwarding feature on a secondary
 server
 may expose primary servers to attacks if they rely on insecure
 IP-address-based
 access control; 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>
 This 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>
 This specifies a list of addresses which the
 server does accept queries from or use to resolve a
 query. Queries
 from these addresses are not responded to. The default
 is <code>none</code>.
 </dd>
<dt>filter-aaaa</dt>
<dd>
 This 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>
 This specifies a list of addresses to which the server
 sends 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>

 This 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
 is used for all clients. If the ACL is defined and
 matches a client, case is 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 treats
 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 matches 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
 does 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 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.) always
 have their case preserved unless the client matches this
 ACL.
 
</dd>
<dt>resolver-query-timeout</dt>
<dd>
 This is the amount of time in seconds that the
 resolver spends 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> results 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 answers 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 listens on all interfaces allowed by the address
 match list. If a port is not specified, port 53 is 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>

 enables 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 listens 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
 listens for incoming queries sent using IPv6. If not specified,
 the server listens 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
 are 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>

 enables the name server on port 53 for any IPv6 addresses
 (with a single wildcard socket),
 and on port 1234 of IPv6 addresses that are not in the prefix
 2001:db8::/32 (with separate sockets for each matched address).
 

 To instruct the server not to 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 does not know the answer to a question, it
 queries 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)
 is used.
 

 If port is * or is omitted,
 a random port number from a pre-configured
 range is picked up and used for each query.
 The port range(s) is 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 checks whether the operating
 system provides a programming interface to retrieve the
 system's default range for ephemeral ports.
 If such an interface is available,
 named uses the corresponding system
 default range; otherwise, it uses 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 are sufficiently large for
 security. A desirable size depends on several 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 is automatically applied when named
 is reloaded.
 Explicit
 configuration of use-v4-udp-ports and
 use-v6-udp-ports is encouraged, 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 do not allow
 named, if run without 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>

 This option 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
 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 overrides
 the options also-notify
 statement. When a zone notify
 statement
 is set to no, the IP
 addresses in the global also-notify list are
 not 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 are 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 are 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 are 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 are terminated. The default is 60
 minutes (1
 hour). The maximum value is 28 days (40320 minutes).
 </dd>
<dt>notify-rate</dt>
<dd>
 This specifies the rate at which NOTIFY requests are 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 is silently raised to one.
 </dd>
<dt>startup-notify-rate</dt>
<dd>
 This is the rate at which NOTIFY requests are sent
 when the name server is first starting up, or when
 zones have been newly added to the name server.
 The default is 20 per second.
 The lowest possible rate is one per second; when set
 to zero, it is silently raised to one.
 </dd>
<dt>serial-query-rate</dt>
<dd>
 Secondary servers periodically query primary
 servers to find out if zone serial numbers have
 changed. Each such query uses a minute amount of
 the secondary 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 is silently raised to one.
 </dd>
<dt>serial-queries</dt>
<dd>
 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 primary 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 one message.
 many-answers is more efficient; the default is many-answers.
 The many-answers format is also supported by
 recent Microsoft Windows name servers.
 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 are
 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; any
 values outside that range are 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>
 This is the maximum number of inbound zone transfers
 that can run concurrently. The default value is <code class="literal">10</code>.
 Increasing transfers-in may
 speed up the convergence
 of secondary zones, but it also may increase the load on the
 local system.
 </dd>
<dt>transfers-out</dt>
<dd>
 This is the maximum number of outbound zone transfers
 that can run concurrently. Zone transfer requests in
 excess
 of the limit are refused. The default value is <code class="literal">10</code>.
 </dd>
<dt>transfers-per-ns</dt>
<dd>
 This is the maximum number of inbound zone transfers
 that can concurrently transfer 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 secondary 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 is 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 is usually 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>
 This option is the same as transfer-source,
 except zone transfers are performed using IPv6.
 </dd>
<dt>alt-transfer-source</dt>
<dd>

 This indicates 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>

 To avoid using the alternate transfer source,
 set use-alt-transfer-source
 appropriately and do not depend upon
 getting an answer back to the first refresh
 query.
 
</div>
</dd>
<dt>alt-transfer-source-v6</dt>
<dd>
 This indicates 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>
 This indicates whether the alternate transfer sources should be used. If views are
 specified, this defaults to no;
 otherwise, it defaults to
 yes.
 </dd>
<dt>notify-source</dt>
<dd>
notify-source
 determines which local source address, and
 optionally UDP port, is used to send NOTIFY
 messages. This address must appear in the secondary
 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>
 This option acts 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 are
 or are 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 are 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 a 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 pass through 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 do not support
 some or
 any of the limits; on such systems, a warning is issued if
 an
 unsupported limit is used.
 
<div class="variablelist"><dl class="variablelist">
<dt>coresize</dt>
<dd>
 This sets the maximum size of a core dump. The default
 is <code class="literal">default</code>.
 </dd>
<dt>datasize</dt>
<dd>
 This sets 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 to limit 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. 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>
 This sets the maximum number of files the server
 may have open concurrently. The default is <code class="literal">unlimited</code>.
 </dd>
<dt>stacksize</dt>
<dd>
 This sets 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 by 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>
 This 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
 are automatically removed. The largest permitted
 value is 2 gigabytes. The default is
 <code class="literal">unlimited</code>, which also
 means 2 gigabytes.
 This option may also be set on a per-zone basis.
 </dd>
<dt>max-records</dt>
<dd>
 This sets the maximum number of records permitted in a zone.
 The default is zero, which means the maximum is unlimited.
 </dd>
<dt>host-statistics-max</dt>
<dd>
 In BIND 8, this specified the maximum number of host statistics
 entries to be kept.
 It is not implemented in BIND 9.
 </dd>
<dt>recursive-clients</dt>
<dd>

 This sets the maximum number (a "hard quota") of simultaneous
 recursive lookups the server performs 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
 are not accepted, and for each incoming request
 a previous pending request is dropped.
 

 A "soft quota" is also set. When this lower
 quota is exceeded, incoming requests are accepted, but
 for each one, a pending request is 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>
 This is the maximum number of simultaneous client TCP
 connections that the server accepts.
 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 accepts
 before dropping additional clients. named attempts to
 self-tune this value and changes are 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 exceeds this value, named
 assumes that it is dealing with a non-responsive zone
 and drops additional queries. If it gets a response
 after dropping queries, it raises the estimate. The
 estimate is then lowered in 20 minutes if it has
 remained unchanged.
 

 If clients-per-query is set to zero,
 there is no limit on the number of clients per query
 and no queries are dropped.
 

 If max-clients-per-query is set to zero,
 there is no upper bound other than imposed by
 recursive-clients.
 
</dd>
<dt>
<a name="fetches-per-zone"></a>fetches-per-zone
</dt>
<dd>

 This sets the maximum number of simultaneous iterative
 queries to any one domain that the server
 permits 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 are all attached
 to the same fetch, up to the
 <code class="option">max-clients-per-query</code> limit,
 and only one iterative query is sent.
 However, when clients are simultaneously
 querying for different names
 or types, multiple queries are 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 are dropped with no response,
 or answered with SERVFAIL. The default is
 <code class="literal">drop</code>.
 

 If fetches-per-zone is set to zero,
 there is no limit on the number of fetches per query
 and no queries are 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>

 This sets the maximum number of simultaneous iterative
 queries that the server allows 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 are 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,
 there is no limit on the number of fetches per query
 and no queries are 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>

 This 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 that BIND recalculates
 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>

 This sets 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 plus
 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> fewer 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>
 This sets the maximum amount of memory to use for the
 server's cache, in bytes or percentage of total physical memory.
 When the amount of data in the cache
 reaches this limit, the server causes records to
 expire prematurely, following an LRU-based strategy, so
 that the limit is not exceeded.
 The keyword <code>unlimited</code>,
 or the value 0, places no limit on the cache size;
 records are purged from the cache only when their
 TTLs expire.
 Any positive values less than 2MB are 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 the amount of physical
 memory is not supported, values represented as a percentage
 fall back to unlimited.
 Note that the detection of physical memory is done only
 once at startup, so named does not
 adjust the cache size if the amount of physical memory
 is changed during runtime.
 </dd>
<dt>tcp-listen-queue</dt>
<dd>
 This sets 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 are queued in kernel space
 waiting for
 some data before being passed to accept. Non-zero values
 less than 10 are 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 removed 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 periodic cleaning anymore.
 Specifying this option therefore has no effect on
 the server's behavior.
 </dd>
<dt>heartbeat-interval</dt>
<dd>
 The server performs 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 occurs.
 </dd>
<dt>interface-interval</dt>
<dd>
 The server scans 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 only occurs when
 the configuration file is loaded, or when
 automatic-interface-scan is enabled
 and supported by the operating system. After the scan, the
 server begins listening for queries on any newly
 discovered interfaces (provided they are allowed by the
 listen-on configuration), and
 stops listening on interfaces that have gone away.
 </dd>
<dt>statistics-interval</dt>
<dd>

 Name server statistics are logged
 every statistics-interval
 minutes. The default is
 60, and the maximum value is 28 days (40320 minutes).
 If set to 0, no statistics are logged.
 
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>

 This option is not 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 topologically 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 normally returns 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. When the addresses in the
 first element overlap, the first rule to match is selected.
 

 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 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 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 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 illustrates reasonable behavior for the
 local host and hosts on directly connected networks. Responses sent to queries from
 the local host favor any of the directly connected
 networks. Responses sent to queries from any other hosts on a
 directly connected network prefer addresses on that same
 network. Responses to other queries are not 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>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>

 While alternating the order of records in a DNS response between
 subsequent queries is a known load distribution technique, certain
 caveats apply (mostly stemming from caching) which usually make it
 a suboptimal choice for load balancing purposes when used on its
 own.
 
</div>

 The rrset-order statement permits configuration
 of the ordering of the records in a multiple-record response. See
 also: <a class="xref" href="Bv9ARM.ch06.html#the_sortlist_statement" title="The sortlist Statement">the section called &#8220;The sortlist Statement&#8221;</a>.
 

 Each rule in an rrset-order statement is defined
 as follows:
 

 [class <code>&lt;class_name&gt;</code>]
 [type <code>&lt;type_name&gt;</code>]
 [name <code>"&lt;domain_name&gt;"</code>]
 order <code>&lt;ordering&gt;</code>
 

 The default qualifiers for each rule are:
 
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
 If no class is specified, the default is
 ANY.
 </li>
<li class="listitem">
 If no type is specified, the default is
 ANY.
 </li>
<li class="listitem">
 If no name is specified, the default is
 * (asterisk).
 </li>
</ul></div>

 

 <code>&lt;domain_name&gt;</code> only matches the name
 itself, not any of its subdomains. To make a rule match all
 subdomains of a given name, a wildcard name
 (<code>*.&lt;domain_name&gt;</code>) must be used.
 Note that <code>*.&lt;domain_name&gt;</code> does
 not match
 <code>&lt;domain_name&gt;</code> itself; to specify
 RRset ordering for a name and all of its subdomains, two separate
 rules must be defined: one for
 <code>&lt;domain_name&gt;</code> and one for
 <code>*.&lt;domain_name&gt;</code>.
 

 The legal values for <code>&lt;ordering&gt;</code>
 are:
 
<div class="variablelist"><dl class="variablelist">
<dt>fixed</dt>
<dd>

 Records are returned in the order they are defined in the zone
 file.
 
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>

 The fixed option is only available if
 BIND is configured with
 --enable-fixed-rrset at compile time.
 
</div>
</dd>
<dt>random</dt>
<dd>
 Records are returned in a random order.
 </dd>
<dt>cyclic</dt>
<dd>
 Records are returned in a cyclic round-robin order, rotating
 by one record per query.
 </dd>
</dl></div>

 By default, records are returned in random order.
 

 Note that if multiple rrset-order statements are
 present in the configuration file (at both the
 options and view levels), they
 are not combined; instead, the more-specific
 one (view) replaces the less-specific one
 (options).
 

 If multiple rules within a single rrset-order
 statement match a given RRset, the first matching rule is applied.
 

 Example:
 
<pre class="programlisting">rrset-order {
 type A name "foo.isc.org" order random;
 type AAAA name "foo.isc.org" order cyclic;
 name "bar.isc.org" order fixed;
 name "*.bar.isc.org" order random;
 name "*.baz.isc.org" order cyclic;
};
</pre>

 With the above configuration, the following RRset ordering is used:
 
<div class="informaltable"><table class="informaltable" border="1">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>QNAME</th>
<th>QTYPE</th>
<th>RRset Order</th>
</tr></thead>
<tbody>
<tr>
<td><code>foo.isc.org</code></td>
<td><code>A</code></td>
<td>random</td>
</tr>
<tr>
<td><code>foo.isc.org</code></td>
<td><code>AAAA</code></td>
<td>cyclic</td>
</tr>
<tr>
<td><code>foo.isc.org</code></td>
<td><code>TXT</code></td>
<td>random</td>
</tr>
<tr>
<td><code>sub.foo.isc.org</code></td>
<td>all</td>
<td>random</td>
</tr>
<tr>
<td><code>bar.isc.org</code></td>
<td>all</td>
<td>fixed</td>
</tr>
<tr>
<td><code>sub.bar.isc.org</code></td>
<td>all</td>
<td>random</td>
</tr>
<tr>
<td><code>baz.isc.org</code></td>
<td>all</td>
<td>random</td>
</tr>
<tr>
<td><code>sub.baz.isc.org</code></td>
<td>all</td>
<td>cyclic</td>
</tr>
</tbody>
</table></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>
 This is always set to 0. More information is available
 in the <a class="link" href="https://kb.isc.org/docs/cve-2021-25219" target="_top">security advisory for CVE-2021-25219</a>.
 </dd>
<dt>servfail-ttl</dt>
<dd>

 This 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 is 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 is
 silently truncated to 7 days if set to a greater value.
 </dd>
<dt>max-cache-ttl</dt>
<dd>
 This sets the maximum time for which the server
 caches 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>

 This sets 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>

 This is not implemented in <acronym class="acronym">BIND</acronym> 9.
 
</div>
</dd>
<dt>sig-validity-interval</dt>
<dd>

 This specifies the number of days into the future that
 DNSSEC signatures that are 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 are
 regenerated. If not specified, the signatures are
 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
 value is 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>
 This specifies 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>
 This specifies a threshold number of signatures that
 terminates 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>

 This specifies a private RDATA type to be used when generating
 signing-state records. The default is
 <code class="literal">65534</code>.
 

 This parameter may be removed
 in a future version, once there is a standard type.
 

 Signing-state records are used 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 primary, giving secondary 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
 secondary 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>

 This 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
 are silently adjusted to the nearest value within
 it. The default value is 1232.
 

 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 advertises 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
 tries again with plain DNS; if that is successful,
 it is taken as evidence that the server does not
 support EDNS. After enough failures using EDNS and
 successes using plain DNS, named
 defaults to plain DNS for future communications
 with that server. If that happens, named
 periodically sends 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 advertises 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 exceed
 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>

 This sets the maximum EDNS UDP message size that
 named sends, in bytes.
 Valid values are 512 to 4096; values outside this
 range are silently adjusted to the nearest
 value within it. The default value is 1232.
 

 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 allow 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 encourages additional
 TCP traffic to the name server.
 
</dd>
<dt>masterfile-format</dt>
<dd>
This 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 secondary zones,
 in which the default value is <code class="constant">raw</code>.
 Files in formats other 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 format other than
 <code class="constant">text</code> is loaded, named
 may omit some of the checks which would be performed for a
 file in <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>

 This 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>
 This 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 recursions 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>
 This 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. The default is 100.
 </dd>
<dt>notify-delay</dt>
<dd>

 This sets the delay, in seconds, between sending sets of NOTIFY
 messages for a zone. The default is 5 seconds.
 

 The overall rate at which NOTIFY messages are sent for all
 zones is controlled by serial-query-rate.
 
</dd>
<dt>max-rsa-exponent-size</dt>
<dd>
 This sets the maximum RSA exponent size, in bits, that is
 accepted when validating. Valid values are 35
 to 4096 bits. The default, zero, 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.
 

 <code class="option">prefetch</code> specifies the
 "trigger" TTL value at which prefetch of the current
 query takes place; when a cache record with a
 lower TTL value is encountered during query processing,
 it is refreshed. Valid trigger TTL values are 1 to
 10 seconds. Values larger than 10 seconds are silently
 reduced to 10.
 Setting a trigger TTL to zero 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 is accepted for a record to be
 eligible for prefetching. The eligibility TTL must
 be at least six seconds longer than the trigger TTL;
 if not, named silently
 adjusts it upward.
 The default eligibility TTL is <code class="literal">9</code>.
 
</dd>
<dt>v6-bias</dt>
<dd>
 When determining the next name server to try,
 this indicates by how many milliseconds to prefer IPv6 name servers.
 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.) 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.
 

 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>

 This is the version the server should report
 via a query of the name <code class="literal">version.bind</code>
 with type TXT and class CHAOS.
 The default is the real version number of this server.
 Specifying version none
 disables processing of the queries.
 

 Setting version to any value
 (including <code class="literal">none</code>) also
 disables queries for <code class="literal">authors.bind TXT CH</code>.
 
</dd>
<dt>hostname</dt>
<dd>
 This is the hostname the server should report via a query of
 the name <code class="filename">hostname.bind</code>
 with type TXT and 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 the queries. Specifying hostname none;
 disables processing of the queries.
 </dd>
<dt>server-id</dt>
<dd>
 This is 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 and class CHAOS.
 The primary purpose of such queries is to
 identify which of a group of anycast servers is actually
 answering the queries. Specifying server-id none;
 disables processing of the queries.
 Specifying server-id hostname; causes 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, for 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 the IPv6 local address (locally assigned),
 IPv6 link local addresses, the IPv6 loopback address, and the
 IPv6 unknown address.
 

 The server attempts to determine if a built-in zone
 already exists or is active (covered by a forward-only
 forwarding declaration) and does not create an empty
 zone if either is true.
 

 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 can be set 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, disable the root zone at the view level. For example:

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

 

 If using the address ranges covered here,
 reverse zones covering the addresses should already be in place.
 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 had
 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 zones under the parent zone they serve. For the real
 root servers, this is all built-in empty zones. This
 enables them to return referrals to deeper in the tree.
 
</div>
<div class="variablelist"><dl class="variablelist">
<dt>empty-server</dt>
<dd>
 This specifies the server name that appears in the returned
 SOA record for empty zones. If none is specified,
 the zone's name is used.
 </dd>
<dt>empty-contact</dt>
<dd>
 This specifies the contact name that appears in the returned
 SOA record for empty zones. If none is specified,
 "." is used.
 </dd>
<dt>empty-zones-enable</dt>
<dd>
 This enables or disables all empty zones. By default, they
 are enabled.
 </dd>
<dt>disable-empty-zone</dt>
<dd>
 This disables 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
 caches an internal shortcut 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.
 

 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 shortcut 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 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 for 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 is 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
 only a single RR), so the
 ordering is not significant.
 

 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 removes 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 occurs.
 </dd>
<dt>max-acache-size</dt>
<dd>
 This is 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
 cleans 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 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 are accepted regardless of the filter
 setting.
 Likewise, if the alias name is a subdomain of the
 corresponding zone, the deny-answer-aliases
 filter does 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 is 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> is silently ignored.
 

 If a response message is rejected due to the filtering,
 the entire message is discarded without being cached, and
 a SERVFAIL error is 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 the user's own network or
 an alias name within the user's 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 the local network
 that could not be externally accessed otherwise.
 See the paper available at
 <a class="link" href="https://dl.acm.org/doi/10.1145/1315245.1315298" target="_top">
 https://dl.acm.org/doi/10.1145/1315245.1315298
 </a>
 for more details about these attacks.
 

 For example, with a domain named "example.net" and
 an internal network using an IPv4 prefix 192.0.2.0/24,
 an administrator 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 let a web browser in the 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 would be
 ignored.
 

 On the other hand, if the browser looked up a legitimate
 internal web server "www.example.net" and the
 following response were returned to
 the <acronym class="acronym">BIND</acronym> 9 server:
 
<pre class="programlisting">www.example.net. A 192.0.2.2</pre>

 it would 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 with having an "external" name
 mapped to an "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 either is not possible or does not make sense to detect
 whether the intent of the mapping is legitimate
 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;
 turning it on is generally discouraged unless there is
 no other choice and the attack is a
 real threat to applications.
 

 Care should be particularly taken if using 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 rejection lists.
 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.
 

 Rules encoded in response policy zones are processed after
 those defined in <a class="link" href="Bv9ARM.ch06.html#access_control" title="Access Control">Access Control Lists
 (ACLs)</a>. All queries from clients which are not
 permitted access to the resolver are answered with a
 status code of REFUSED, regardless of configured RPZ rules.
 

 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
 the 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. The
 nsdname-enable phrase turns NSDNAME
 triggers off or on for a single policy zone or for all
 zones.
 

 If authoritative nameservers for the query name are not
 yet known, named recursively
 looks up the authoritative servers for the query name
 before applying an RPZ-NSDNAME rule,
 which can cause a processing delay. To speed up
 processing at the cost of precision, the
 nsdname-wait-recurse option
 can be used; when set to <code>no</code>,
 RPZ-NSDNAME rules are only applied when authoritative
 servers for the query name have already been looked up and
 cached. If authoritative servers for the query name
 are not in the cache, the RPZ-NSDNAME rule is
 ignored, but the authoritative servers for the query name
 are looked up in the background and the rule is
 applied to subsequent queries. The default is
 <code>yes</code>, meaning RPZ-NSDNAME
 rules are always applied, even if authoritative
 servers for the query name need to be looked up first.
 
</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 recursively looks up
 the IP address before applying an RPZ-NSIP rule,
 which 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 are only applied when a name
 server's IP address has already been looked up and
 cached. If a server's IP address is not in the
 cache, the RPZ-NSIP rule is ignored,
 but the address is looked up in the
 background and the rule is applied
 to subsequent queries. The default is
 <code>yes</code>, meaning RPZ-NSIP
 rules are always 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
 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 auto-acceptance 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 auto-rejection 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 a
 CNAME whose target is the wildcard top-level
 domain (<code class="literal">*.</code>).
 It rewrites the response to NODATA or ANCOUNT=0.
 </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 an ordinary CNAME after the asterisk (*)
 has been replaced with the query name.
 This special form is useful for query logging in the
 walled garden's authoritative 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 is written (or not)
 according to any triggered policy records that are not
 disabled.
 Disabled policy zones should appear first,
 because they are often not logged
 if a higher-precedence trigger is found first.
 </dd>
<dt>
PASSTHRU, DROP, TCP-Only, NXDOMAIN, NODATA
</dt>
<dd>
 each override 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 for
 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 the requested 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 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
 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 the policy zone. It is then limited
 to a maximum value.
 The max-policy-ttl clause changes the
 maximum number of seconds from its default of 5.
 

 For example, an administrator 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   .

; auto-reject and auto-accept 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">BIND</acronym> 9 server with adequate memory and one
 response policy zone with QNAME and IP triggers might achieve a
 maximum queries-per-second (QPS) 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
 to amplify 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 responses
 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 which 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 address 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 rejection lists.
 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 resulting 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.
 Rather, all responses are dropped.
 A value of 1 causes every response to slip;
 values between 2 and 10 cause every nth 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,
 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.
 

 Communities of DNS clients can be given their own parameters or no
 rate limiting by putting
 rate-limit statements in view
 statements instead of in the global option
 statement.
 A rate-limit statement in a view replaces,
 rather than supplements, 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 SMTP Mail From
 command. Web browsers often repeatedly resolve the
 same names that are duplicated in HTML &lt;IMG&gt; tags
 in a page. all-per-second is similar
 to the rate limiting offered by firewalls but is 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><div><h4 class="title">
<a name="nxdomain_redirect"></a>NXDOMAIN Redirection</h4></div></div></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 either method, when named gets an 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 both the original NXDOMAIN response and
 the replacement data (or a NXDOMAIN indicating that there
 is no replacement) must be stored.
 

 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 a remote server is giving out bad data,
 marking it as bogus prevents further queries to it. The
 default
 value of bogus is no.
 

 The provide-ixfr clause determines
 whether
 the local server, acting as primary, responds with an
 incremental
 zone transfer when the given remote server, a secondary, requests it.
 If set to yes, incremental transfer
 is provided
 whenever possible. If set to no,
 all transfers
 to the remote server are 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 secondary, requests incremental zone
 transfers from the given remote server, a primary. 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; if set there, it
 overrides the global or view setting for that zone.
 

 IXFR requests to servers that do not support IXFR
 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
 primary
 and secondary 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 secondary,
 requests the EDNS EXPIRE value. The EDNS EXPIRE value
 indicates the remaining time before the zone data
 expires and needs to 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 attempts 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 are silently
 adjusted to the nearest value within it. This option
 is useful when advertising a different value
 to this server than the value advertised 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 does 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 is 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 are silently
 adjusted. This option is not needed until higher
 EDNS versions than 0 are in use.
 

 The max-udp-size option sets the
 maximum EDNS UDP message size named
 sends. Valid values are 512 to 4096 bytes; values
 outside this range are silently adjusted. This
 option is useful when 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 single message, which is
 more efficient. It is possible to specify which method
 to use for a server via the transfer-format option;
 If not set there, the transfer-format
 specified
 by the options statement is
 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
 is 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, respectively, to be used for zone transfer with the remote server.
 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, respectively, to be used for notify
 messages sent to remote servers. 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, respectively, to be used for queries
 sent to remote servers. 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 adds an 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 adds 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 on
 the name server.
 

 This statement is intended 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 fails 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 are
 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.
 

 Attempts to open a statistics channel are
 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 does 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.
 

 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 has 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
 is not used.
 

 The trusted-keys statement can contain
 multiple key entries, each consisting of the key's
 domain name, flags, protocol, and 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 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; it would
 reply with a SERVFAIL response code. This would
 continue until the resolver operator updated the
 trusted-keys statement with the new key.
 

 If, however, the zone were listed in a
 managed-keys statement instead, 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 statement, differing
 by the presence of the second field, which contains 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, simply moves on. The
 key specified in the managed-keys
 statement is not used to validate answers; it is
 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 is removed from the managed-keys database,
 and RFC 5011 key maintenance is no longer 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 is a separate managed-keys database for each
 view; the filename is 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 are 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 zone file as soon as
 possible afterward, usually within 30
 seconds. 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
 automatically initializes 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 is 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 match that view.
 The order of the view statements is
 significant;
 a client request is resolved in the context of the first
 view that it matches.
 

 Zones defined within a view
 statement are
 only 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
 applies 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-selfsub | krb5-subdomain | ms-self | ms-selfsub | 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> ); ... };
	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 are: <code class="varname">master</code>,
 <code class="varname">slave</code>, <code class="varname">hint</code>,
 <code class="varname">stub</code>, <code class="varname">static-stub</code>,
 <code class="varname">forward</code>, <code class="varname">redirect</code>,
 or <code class="varname">delegation-only</code>.
 
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
 Later versions of BIND added type primary
 and type secondary as synonyms for
 type master and type slave,
 as those terms are in more common use now. BIND 9.11's
 configuration syntax predates this change.
 </div>
<div class="informaltable"><table class="informaltable" border="1">
<colgroup>
<col class="1">
<col class="2">
</colgroup>
<tbody valign="top">
<tr>
<td valign="top">
 
 <code class="varname">master</code>
 
 </td>
<td valign="top">
 
 The server has a master copy of the data
 for the zone and is able to provide authoritative
 answers for it.
 
 </td>
</tr>
<tr>
<td valign="top">
 
 <code class="varname">slave</code>
 
 </td>
<td valign="top">
 
 A secondary zone, replicating a primary zone
 provided by another authoritative server.
 The masters list
 specifies one or more IP addresses
 of primary servers that the secondary 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 primary can also be done with
 per-server TSIG keys.
 If a file is specified, then the
 replica is 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 secondary 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 there are 100000 files in
 a single directory.)
 
 </td>
</tr>
<tr>
<td valign="top">
 
 <code class="varname">hint</code>
 
 </td>
<td valign="top">
 
 The initial set of root name servers is
 specified using a hint zone. When the server starts,
 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 default hints.
 
 </td>
</tr>
<tr>
<td valign="top">
 
 <code class="varname">stub</code>
 
 </td>
<td valign="top">
 
 A stub zone is similar to a secondary zone,
 except that it replicates only the NS records of a
 primary 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 a 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.
 If a <acronym class="acronym">BIND</acronym> 9 primary, serving a parent
 zone, has child stub zones configured, all the secondary
 servers for the
 parent zone also need to have the same child stub
 zones
 configured.

Stub zones can also be used as a way to force 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
 RFC 1918 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 valign="top">
 
 <code class="varname">static-stub</code>
 
 </td>
<td valign="top">
 
 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 primary server; and
 when recursion is necessary for a query that
 matches a static-stub zone, the locally
 configured data (name server 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 are responded to 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 valign="top">
 
 <code class="varname">forward</code>
 
 </td>
<td valign="top">
 
 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 applies 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 is done for the domain, canceling the
 effects of
 any forwarders in the options statement. Thus,
 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
 use the same
 servers as set globally, re-specify the
 global forwarders.
 
 </td>
</tr>
<tr>
<td valign="top">
 
 <code class="varname">redirect</code>
 
 </td>
<td valign="top">
 
 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, no substitution
 occurs.
 
 
 To redirect all NXDOMAIN responses to
 100.100.100.2 and
 2001:ffff:ffff::100.100.100.2,
 configure a type <code class="varname">redirect</code> 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>.
 
 
 As another example, to redirect all Spanish names (under .ES),
 use similar entries but with the names
 "*.ES." instead of "*.". To redirect all
 commercial Spanish names (under COM.ES),
 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 primary and secondary
 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 are reloaded along
 with other zones.
 
 </td>
</tr>
<tr>
<td valign="top">
 
 <code class="varname">delegation-only</code>
 
 </td>
<td valign="top">
 
 This zone type 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 is treated
 as NXDOMAIN. This does not apply to the
 zone apex, and 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>
<tr>
<td valign="top">
 
 <code class="varname">in-view</code>
 
 </td>
<td valign="top">
 
 When using multiple views, a primary or secondary zone
 configured in one view can be referenced in a
 subsequent view. This allows both views to serve the
 same zone without the overhead of loading it more
 than once. This is configured using a
 <code class="varname">zone</code> statement, with an
 <code class="varname">in-view</code> option specifying the
 view in which the zone is defined.
 A <code class="varname">zone</code> statement containing
 <code class="varname">in-view</code> does not need to specify
 a type, since that is part of the zone definition
 in the other view.
 
 
 See <a class="xref" href="Bv9ARM.ch06.html#multiple_views" title="Multiple Views">the section called &#8220;Multiple Views&#8221;</a> for more information.
 
 </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 was
 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>
 This 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>
 This option is only meaningful if notify
 is
 active for this zone. The set of machines that
 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) 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 zone files and/or DNS responses
 received from the
 network. The default varies according to zone type.
 For primary zones the default is fail;
 for secondary 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>

 This specifies the type of database to be used to store 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>

 This flag only applies to forward, hint, and stub
 zones. If set to <code>yes</code>,
 then the zone is 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>
 This sets 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>
 This option is 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
 allows a normal lookup to be tried.
 </dd>
<dt>forwarders</dt>
<dd>
 This is 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>
 This 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>
 This was an undocumented option in <acronym class="acronym">BIND</acronym> 8.
 It is ignored in <acronym class="acronym">BIND</acronym> 9.
 </dd>
<dt>journal</dt>
<dd>
 This allows 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 primary (master)
 and secondary (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 to specify
 a public zone key for verification of signatures in DNSSEC-signed
 zones when they were 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>

 This option is 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 internally
 configures 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 are 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 used internally 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
 initiates recursive resolution and sends
 queries to 192.0.2.1 and/or 2001:db8::1234.
 
</dd>
<dt>server-names</dt>
<dd>

 This option is only meaningful for static-stub zones.
 This is a list of domain names of name servers that
 act as authoritative servers of the static-stub
 zone.
 These names are resolved to IP addresses when
 named needs to send queries to
 these servers.
 For this supplemental resolution to be successful,
 these names must not be a subdomain of the origin
 name of the 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; it is rejected by
 the configuration parser.
 

 A non-empty list for this option internally
 configures 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 are internally configured:
 
<pre class="programlisting">example.com. NS ns1.example.net.
example.com. NS ns2.example.net.
</pre>

 These records are used internally 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
 initiates recursive resolution,
 resolves "ns1.example.net" and/or
 "ns2.example.net" to IP addresses, and then sends
 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 descriptions 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
 choices of <code>master</code> and
 <code>slave</code> 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 an
 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
 methods of granting clients the right to perform
 dynamic updates to a zone, configured by the
 allow-update and
 update-policy options.
 

 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 which 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 primary zones (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;.
 named automatically generates a TSIG session
 key when starting and stores 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 is 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 are permitted to send
 updates.
 

 Note that only one session key is generated by
 named; all zones configured to use
 update-policy local 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
 represents 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 is
 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 16
 values:
 <code class="varname">name</code>, <code class="varname">subdomain</code>,
 <code class="varname">zonesub</code>, <code class="varname">wildcard</code>,
 <code class="varname">self</code>, <code class="varname">selfsub</code>,
 <code class="varname">selfwild</code>, <code class="varname">ms-self</code>,
 <code class="varname">ms-selfsub</code>, <code class="varname">ms-subdomain</code>,
 <code class="varname">krb5-self</code>, <code class="varname">krb5-selfsub</code>,
 <code class="varname">krb5-subdomain</code>, <code class="varname">tcp-self</code>,
 <code class="varname">6to4-self</code>, and <code class="varname">external</code>.
 
<div class="informaltable"><table class="informaltable" 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>
 
 With 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>
 (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-selfsub</code>
 
 </td>
<td>
 
 This is similar to ms-self,
 except it also allows updates to any subdomain of
 the name specified in the Windows machine
 principal, not just to the name itself.
 
 </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> is
 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 an 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-selfsub</code>
 
 </td>
<td>
 
 This is similar to krb5-self,
 except it also allows updates to any subdomain of
 the name specified in the "machine" part of the
 Kerberos principal, not just to the name itself.
 
 </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 matches 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
 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
 , with the exception of forward
 and forwarders. (These options control
 the behavior of the containing view, rather than change
 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. Be
 careful 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 type 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-1.7.4.2.3"></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 class="informaltable" 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 an 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>

 For a complete list of types of valid RRs,
 including those that have been obsoleted,
 please refer to https://en.wikipedia.org/wiki/List_of_DNS_record_types.
 

 The following classes of resource records
 are currently valid in the DNS:
 
<div class="informaltable"><table class="informaltable" 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.
 It was rarely used for its historical purpose, but was 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 was used to share
 information
 about various systems databases, such as users,
 groups, printers,
 etc.
 
 </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 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; that also times out, but follows 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, 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 zone 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 are 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. 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 interest of clarity.
 

 The resource data or RDATA section of the RR is given using
 knowledge of the typical representation for the data.
 

 For example, the RRs carried in a message might be shown as:
 
<div class="informaltable"><table class="informaltable" 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.
 

 Here is another possible example:
 
<div class="informaltable"><table class="informaltable" 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 falls back to the next largest
 priority.
 Priority numbers do not have any absolute meaning; they are
 relevant
 only respective to other MX records for that domain name. The
 domain
 name given is the machine to which the mail is delivered.
 It must have an associated address record
 (A or AAAA); 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 is ignored.
 Instead,
 the mail is delivered to the server specified in the MX
 record
 pointed to by the CNAME.
 For example:
 
<div class="informaltable"><table class="informaltable" 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 is attempted to <code class="literal">mail.example.com</code> and
 <code class="literal">mail2.example.com</code> (in
 any order); if neither of those succeeds, delivery to <code class="literal">mail.backup.org</code>
 is 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- (TTL) 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 an RR can be cached before it
 should be discarded. The following three types of TTLs are
 currently
 used in a zone file.
 
<div class="informaltable"><table class="informaltable" 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
 cache no-such-domain
 (NXDOMAIN) responses from this server.
 
 
 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 controls 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 class="informaltable" 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 line in this example
 is only to provide context; it does not
 necessarily
 appear in the actual usage. It is 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 DNS "master file" format was initially defined in RFC 1035 and
 has subsequently been extended. While the format
 itself
 is class-independent, all records in a zone 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 a
 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 is appended to any
 unqualified records. When a zone is first read, there
 is an implicit $ORIGIN
 &lt;<code class="varname">zone_name</code>&gt;.;
 note the 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> ]
 

 This reads and processes the file <code class="filename">filename</code> as
 if it were included in 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> ]
 

 This sets 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> Primary 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>

 Both generate a set of A and MX records. Note the MX's right-hand
 side is a quoted string. The quotes are 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 class="informaltable" 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, 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 in
 ${offset[,width[,base]]}.
 For example, ${-20,3,d}
 subtracts 20 from the current value and 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 is treated as
 if it were 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>
 
 This specifies the time-to-live of the generated records. If
 not specified, this is inherited using the
 normal TTL inheritance rules.
 
 class
 and ttl can be
 entered in either order.
 
 </td>
</tr>
<tr>
<td>
 class
 </td>
<td>
 
 This 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>
 
 This can be any valid type.
 
 </td>
</tr>
<tr>
<td>
 rhs
 </td>
<td>
 
 rhs is an 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 text 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 can be loaded
 directly into memory via the mmap()
 function and 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, the zone file is automatically
 generated when
 named dumps the zone contents after
 zone transfer or when applying prior updates, if one of these formats is specified by the
 masterfile-format option.
 

 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. Make any
 necessary modifications to the text file, and
 then convert it to the binary form via 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>BIND 9 Statistics</h2></div></div></div>

 <acronym class="acronym">BIND</acronym> 9 maintains lots of statistics
 information and provides several interfaces for users to
 access those statistics.
 The available statistics include all statistics counters
 that 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 class="informaltable" 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 for 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 for name resolutions
 performed in the internal resolver,
 maintained per view.
 
 </td>
</tr>
<tr>
<td>
 Cache DB RRsets
 </td>
<td>
 
 Statistics counters related to cache contents,
 maintained per view.
 
 
 The "NXDOMAIN" counter is the number of names
 that have been cached as nonexistent.
 Counters named for RR types indicate the
 number of active RRsets for each type in the cache
 database.
 
 
 If an RR type name is preceded by an exclamation
 point (!), it represents the number of records in the
 cache which indicate that the type does not exist
 for a particular name; this is also known as "NXRRSET".
 If an RR type name is preceded by a hash mark (#), it
 represents the number of RRsets for this type that are
 present in the cache but whose TTLs have expired; these
 RRsets may only be used if stale answers are enabled.
 If an RR type name is preceded by a tilde (~), it
 represents the number of RRsets for this type that are
 present in the cache database but are marked for garbage
 collection; these RRsets cannot be used.
 
 </td>
</tr>
<tr>
<td>
 Socket I/O Statistics
 </td>
<td>
 
 Statistics counters for 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 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 in 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 the 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, may be slightly modified
 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 class="informaltable" 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>
 
 BIND 8 Symbol
 
 </td>
<td>
 
 Description
 
 </td>
</tr>
<tr>
<td>
 Requestv4
 </td>
<td>
 RQ
 </td>
<td>
 
 This indicates the number of IPv4 requests received.
 Note: this also counts non-query requests.
 
 </td>
</tr>
<tr>
<td>
 Requestv6
 </td>
<td>
 RQ
 </td>
<td>
 
 This indicates the number of IPv6 requests received.
 Note: this also counts non-query requests.
 
 </td>
</tr>
<tr>
<td>
 ReqEdns0
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of requests received with EDNS(0).
 
 </td>
</tr>
<tr>
<td>
 ReqBadEDNSVer
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of requests received with an unsupported EDNS version.
 
 </td>
</tr>
<tr>
<td>
 ReqTSIG
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of requests received with TSIG.
 
 </td>
</tr>
<tr>
<td>
 ReqSIG0
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of requests received with SIG(0).
 
 </td>
</tr>
<tr>
<td>
 ReqBadSIG
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of requests received with an invalid (TSIG or SIG(0)) signature.
 
 </td>
</tr>
<tr>
<td>
 ReqTCP
 </td>
<td>
 RTCP
 </td>
<td>
 
 This indicates the number of TCP requests received.
 
 </td>
</tr>
<tr>
<td>
 AuthQryRej
 </td>
<td>
 RUQ
 </td>
<td>
 
 This indicates the number of rejected authoritative (non-recursive) queries.
 
 </td>
</tr>
<tr>
<td>
 RecQryRej
 </td>
<td>
 RURQ
 </td>
<td>
 
 This indicates the number of rejected recursive queries.
 
 </td>
</tr>
<tr>
<td>
 XfrRej
 </td>
<td>
 RUXFR
 </td>
<td>
 
 This indicates the number of rejected zone transfer requests.
 
 </td>
</tr>
<tr>
<td>
 UpdateRej
 </td>
<td>
 RUUpd
 </td>
<td>
 
 This indicates the number of rejected dynamic update requests.
 
 </td>
</tr>
<tr>
<td>
 Response
 </td>
<td>
 SAns
 </td>
<td>
 
 This indicates the number of responses sent.
 
 </td>
</tr>
<tr>
<td>
 RespTruncated
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of truncated responses sent.
 
 </td>
</tr>
<tr>
<td>
 RespEDNS0
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of responses sent with EDNS(0).
 
 </td>
</tr>
<tr>
<td>
 RespTSIG
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of responses sent with TSIG.
 
 </td>
</tr>
<tr>
<td>
 RespSIG0
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of responses sent with SIG(0).
 
 </td>
</tr>
<tr>
<td>
 QrySuccess
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of queries that resulted in a successful answer,
 meaning queries which return 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>
 
 This indicates the number of queries that resulted in an authoritative answer.
 
 </td>
</tr>
<tr>
<td>
 QryNoauthAns
 </td>
<td>
 SNaAns
 </td>
<td>
 
 This indicates the number of queries that resulted in a non-authoritative answer.
 
 </td>
</tr>
<tr>
<td>
 QryReferral
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of queries that resulted in a 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>
 
 This indicates the number of queries that 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>
 
 This indicates the number of queries that resulted in SERVFAIL.
 
 </td>
</tr>
<tr>
<td>
 QryFORMERR
 </td>
<td>
 SFErr
 </td>
<td>
 
 This indicates the number of queries that resulted in FORMERR.
 
 </td>
</tr>
<tr>
<td>
 QryNXDOMAIN
 </td>
<td>
 SNXD
 </td>
<td>
 
 This indicates the number of queries that 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>
 
 This indicates the number of queries that 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>
 
 This indicates the number of queries which the server attempted to
 recurse but for which it 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>
 
 This indicates the number of recursive queries for which the server
 discovered an excessive number of existing
 recursive queries for the same name, type, and
 class, and which 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>
 
 This indicates the number of 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, more fine-grained counters such as
 AuthQryRej and
 RecQryRej
 that would also fall into this counter are provided,
 so this counter is not of much
 interest in practice.
 
 </td>
</tr>
<tr>
<td>
 QryNXRedir
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of queries that resulted in NXDOMAIN that were redirected.
 
 </td>
</tr>
<tr>
<td>
 QryNXRedirRLookup
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of queries that resulted in NXDOMAIN that were redirected
 and resulted in a successful remote lookup.
 
 </td>
</tr>
<tr>
<td>
 XfrReqDone
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of requested and completed zone transfers.
 
 </td>
</tr>
<tr>
<td>
 UpdateReqFwd
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of forwarded update requests.
 
 </td>
</tr>
<tr>
<td>
 UpdateRespFwd
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of forwarded update responses.
 
 </td>
</tr>
<tr>
<td>
 UpdateFwdFail
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of forwarded dynamic updates that failed.
 
 </td>
</tr>
<tr>
<td>
 UpdateDone
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of completed dynamic updates.
 
 </td>
</tr>
<tr>
<td>
 UpdateFail
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of failed dynamic updates.
 
 </td>
</tr>
<tr>
<td>
 UpdateBadPrereq
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of dynamic updates rejected due to a prerequisite failure.
 
 </td>
</tr>
<tr>
<td>
 RateDropped
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of responses dropped due to rate limits.
 
 </td>
</tr>
<tr>
<td>
 RateSlipped
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of responses truncated by rate limits.
 
 </td>
</tr>
<tr>
<td>
 RPZRewrites
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of 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 class="informaltable" 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>
 
 This indicates the number of IPv4 notifies sent.
 
 </td>
</tr>
<tr>
<td>
 NotifyOutv6
 </td>
<td>
 
 This indicates the number of IPv6 notifies sent.
 
 </td>
</tr>
<tr>
<td>
 NotifyInv4
 </td>
<td>
 
 This indicates the number of IPv4 notifies received.
 
 </td>
</tr>
<tr>
<td>
 NotifyInv6
 </td>
<td>
 
 This indicates the number of IPv6 notifies received.
 
 </td>
</tr>
<tr>
<td>
 NotifyRej
 </td>
<td>
 
 This indicates the number of incoming notifies rejected.
 
 </td>
</tr>
<tr>
<td>
 SOAOutv4
 </td>
<td>
 
 This indicates the number of IPv4 SOA queries sent.
 
 </td>
</tr>
<tr>
<td>
 SOAOutv6
 </td>
<td>
 
 This indicates the number of IPv6 SOA queries sent.
 
 </td>
</tr>
<tr>
<td>
 AXFRReqv4
 </td>
<td>
 
 This indicates the number of requested IPv4 AXFRs.
 
 </td>
</tr>
<tr>
<td>
 AXFRReqv6
 </td>
<td>
 
 This indicates the number of requested IPv6 AXFRs.
 
 </td>
</tr>
<tr>
<td>
 IXFRReqv4
 </td>
<td>
 
 This indicates the number of requested IPv4 IXFRs.
 
 </td>
</tr>
<tr>
<td>
 IXFRReqv6
 </td>
<td>
 
 This indicates the number of requested IPv6 IXFRs.
 
 </td>
</tr>
<tr>
<td>
 XfrSuccess
 </td>
<td>
 
 This indicates the number of successful zone transfer requests.
 
 </td>
</tr>
<tr>
<td>
 XfrFail
 </td>
<td>
 
 This indicates the number of failed zone transfer requests.
 
 </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 class="informaltable"><table class="informaltable" 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>
 
 BIND 8 Symbol
 
 </td>
<td>
 
 Description
 
 </td>
</tr>
<tr>
<td>
 Queryv4
 </td>
<td>
 SFwdQ
 </td>
<td>
 
 This indicates the number of IPv4 queries sent.
 
 </td>
</tr>
<tr>
<td>
 Queryv6
 </td>
<td>
 SFwdQ
 </td>
<td>
 
 This indicates the number of IPv6 queries sent.
 
 </td>
</tr>
<tr>
<td>
 Responsev4
 </td>
<td>
 RR
 </td>
<td>
 
 This indicates the number of IPv4 responses received.
 
 </td>
</tr>
<tr>
<td>
 Responsev6
 </td>
<td>
 RR
 </td>
<td>
 
 This indicates the number of IPv6 responses received.
 
 </td>
</tr>
<tr>
<td>
 NXDOMAIN
 </td>
<td>
 RNXD
 </td>
<td>
 
 This indicates the number of NXDOMAINs received.
 
 </td>
</tr>
<tr>
<td>
 SERVFAIL
 </td>
<td>
 RFail
 </td>
<td>
 
 This indicates the number of SERVFAILs received.
 
 </td>
</tr>
<tr>
<td>
 FORMERR
 </td>
<td>
 RFErr
 </td>
<td>
 
 This indicates the number of FORMERRs received.
 
 </td>
</tr>
<tr>
<td>
 OtherError
 </td>
<td>
 RErr
 </td>
<td>
 
 This indicates the number of other errors received.
 
 </td>
</tr>
<tr>
<td>
 EDNS0Fail
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of EDNS(0) query failures.
 
 </td>
</tr>
<tr>
<td>
 Mismatch
 </td>
<td>
 RDupR
 </td>
<td>
 
 This indicates the number of mismatched responses received,
 meaning the DNS ID, response's source address,
 and/or the response's source port does not
 match what was expected.
 (The port must be 53 or as defined by
 the port option.)
 This may be an indication of a cache
 poisoning attempt.
 
 </td>
</tr>
<tr>
<td>
 Truncated
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of truncated responses received.
 
 </td>
</tr>
<tr>
<td>
 Lame
 </td>
<td>
 RLame
 </td>
<td>
 
 This indicates the number of lame delegations received.
 
 </td>
</tr>
<tr>
<td>
 Retry
 </td>
<td>
 SDupQ
 </td>
<td>
 
 This indicates the number of query retries performed.
 
 </td>
</tr>
<tr>
<td>
 QueryAbort
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of queries aborted due to quota control.
 
 </td>
</tr>
<tr>
<td>
 QuerySockFail
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of failures in opening query sockets.
 One common reason for such failures is a
 due to a limitation on file descriptors.
 
 </td>
</tr>
<tr>
<td>
 QueryTimeout
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of query timeouts.
 
 </td>
</tr>
<tr>
<td>
 GlueFetchv4
 </td>
<td>
 SSysQ
 </td>
<td>
 
 This indicates the number of IPv4 NS address fetches invoked.
 
 </td>
</tr>
<tr>
<td>
 GlueFetchv6
 </td>
<td>
 SSysQ
 </td>
<td>
 
 This indicates the number of IPv6 NS address fetches invoked.
 
 </td>
</tr>
<tr>
<td>
 GlueFetchv4Fail
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of failed IPv4 NS address fetches.
 
 </td>
</tr>
<tr>
<td>
 GlueFetchv6Fail
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of failed IPv6 NS address fetches.
 
 </td>
</tr>
<tr>
<td>
 ValAttempt
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of attempted DNSSEC validations.
 
 </td>
</tr>
<tr>
<td>
 ValOk
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of successful DNSSEC validations.
 
 </td>
</tr>
<tr>
<td>
 ValNegOk
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of successful DNSSEC validations on negative information.
 
 </td>
</tr>
<tr>
<td>
 ValFail
 </td>
<td>
 
 </td>
<td>
 
 This indicates the number of failed DNSSEC validations.
 
 </td>
</tr>
<tr>
<td>
 QryRTTnn
 </td>
<td>
 
 </td>
<td>
 
 This provides a frequency table on query round-trip times (RTTs).
 Each nn specifies the corresponding
 frequency.
 In the sequence of
 nn_1,
 nn_2,
 ...,
 nn_m,
 the value of nn_i is the
 number of queries whose RTTs are between
 nn_(i-1) (inclusive) and
 nn_i (exclusive) milliseconds.
 For the sake of convenience, we define
 nn_0 to be 0.
 The last entry should be represented as
 nn_m+, which means the
 number of queries whose RTTs are equal to or greater than
 nn_m milliseconds.
 
 </td>
</tr>
</tbody>
</table></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
 type, 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 class="informaltable" 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>
 
 This indicates the number of sockets opened successfully.
 This counter does not apply to the
 FDwatch type.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;OpenFail
 </td>
<td>
 
 This indicates the number of failures to open sockets.
 This counter does not apply to the
 FDwatch type.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;Close
 </td>
<td>
 
 This indicates the number of closed sockets.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;BindFail
 </td>
<td>
 
 This indicates the number of failures to bind sockets.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;ConnFail
 </td>
<td>
 
 This indicates the number of failures to connect sockets.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;Conn
 </td>
<td>
 
 This indicates the number of connections established successfully.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;AcceptFail
 </td>
<td>
 
 This indicates the number of failures to accept incoming connection requests.
 This counter does not apply to the
 UDP and
 FDwatch types.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;Accept
 </td>
<td>
 
 This indicates the number of incoming connections successfully accepted.
 This counter does not apply to the
 UDP and
 FDwatch types.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;SendErr
 </td>
<td>
 
 This indicates the number of errors in socket send operations.
 This counter corresponds
 to the SErr counter of
 BIND 8.
 
 </td>
</tr>
<tr>
<td>
 &lt;TYPE&gt;RecvErr
 </td>
<td>
 
 This indicates the number of errors in socket receive operations,
 including 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.
 </dd>
</dl></div>
</div>
</div>
</div>
</div>
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