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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">
<p><b>Table of Contents</b></p>
<dl class="toc">
<dt><span class="section"><a href="Bv9ARM.ch06.html#configuration_file_elements">Configuration File Elements</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch06.html#address_match_lists">Address Match Lists</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#comment_syntax">Comment Syntax</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="Bv9ARM.ch06.html#Configuration_File_Grammar">Configuration File Grammar</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch06.html#acl_grammar"><span class="command"><strong>acl</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#acl"><span class="command"><strong>acl</strong></span> Statement Definition and
Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#controls_grammar"><span class="command"><strong>controls</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#controls_statement_definition_and_usage"><span class="command"><strong>controls</strong></span> Statement Definition and
Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#include_grammar"><span class="command"><strong>include</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#include_statement"><span class="command"><strong>include</strong></span> Statement Definition and Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#key_grammar"><span class="command"><strong>key</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#key_statement"><span class="command"><strong>key</strong></span> Statement Definition and Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#logging_grammar"><span class="command"><strong>logging</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#logging_statement"><span class="command"><strong>logging</strong></span> Statement Definition and Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#lwres_grammar"><span class="command"><strong>lwres</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#lwres_statement"><span class="command"><strong>lwres</strong></span> Statement Definition and Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#masters_grammar"><span class="command"><strong>masters</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#masters_statement"><span class="command"><strong>masters</strong></span> Statement Definition and
Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#options_grammar"><span class="command"><strong>options</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#options"><span class="command"><strong>options</strong></span> Statement Definition and
Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#server_statement_grammar"><span class="command"><strong>server</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#server_statement_definition_and_usage"><span class="command"><strong>server</strong></span> Statement Definition and
Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#statschannels"><span class="command"><strong>statistics-channels</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#statistics_channels"><span class="command"><strong>statistics-channels</strong></span> Statement Definition and
Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#trusted-keys"><span class="command"><strong>trusted-keys</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#trusted_keys"><span class="command"><strong>trusted-keys</strong></span> Statement Definition
and Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#managed_keys"><span class="command"><strong>managed-keys</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#managed-keys"><span class="command"><strong>managed-keys</strong></span> Statement Definition
and Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#view_statement_grammar"><span class="command"><strong>view</strong></span> Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#view_statement"><span class="command"><strong>view</strong></span> Statement Definition and Usage</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#zone_statement_grammar"><span class="command"><strong>zone</strong></span>
Statement Grammar</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#zone_statement"><span class="command"><strong>zone</strong></span> Statement Definition and Usage</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="Bv9ARM.ch06.html#zone_file">Zone File</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch06.html#types_of_resource_records_and_when_to_use_them">Types of Resource Records and When to Use Them</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#mx_records">Discussion of MX Records</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#Setting_TTLs">Setting TTLs</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#ipv4_reverse">Inverse Mapping in IPv4</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#zone_directives">Other Zone File Directives</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#generate_directive"><acronym class="acronym">BIND</acronym> Master File Extension: the <span class="command"><strong>$GENERATE</strong></span> Directive</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#zonefile_format">Additional File Formats</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="Bv9ARM.ch06.html#statistics">BIND9 Statistics</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch06.html#statsfile">The Statistics File</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch06.html#statistics_counters">Statistics Counters</a></span></dt>
</dl></dd>
</dl>
</div>
<p>
<acronym class="acronym">BIND</acronym> 9 configuration is broadly similar
to <acronym class="acronym">BIND</acronym> 8; however, there are a few new
areas
of configuration, such as views. <acronym class="acronym">BIND</acronym>
8 configuration files should work with few alterations in <acronym class="acronym">BIND</acronym>
9, although more complex configurations should be reviewed to check
if they can be more efficiently implemented using the new features
found in <acronym class="acronym">BIND</acronym> 9.
</p>
<p>
<acronym class="acronym">BIND</acronym> 4 configuration files can be
converted to the new format
using the shell script
<code class="filename">contrib/named-bootconf/named-bootconf.sh</code>.
</p>
<div class="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>
<p>
Following is a list of elements used throughout the <acronym class="acronym">BIND</acronym> configuration
file documentation:
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.855in" class="1">
<col width="3.770in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p>
<code class="varname">acl_name</code>
</p>
</td>
<td>
<p>
The name of an <code class="varname">address_match_list</code> as
defined by the <span class="command"><strong>acl</strong></span> statement.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">address_match_list</code>
</p>
</td>
<td>
<p>
A list of one or more
<code class="varname">ip_addr</code>,
<code class="varname">ip_prefix</code>, <code class="varname">key_id</code>,
or <code class="varname">acl_name</code> elements, see
<a class="xref" href="Bv9ARM.ch06.html#address_match_lists" title="Address Match Lists">the section called “Address Match Lists”</a>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">masters_list</code>
</p>
</td>
<td>
<p>
A named list of one or more <code class="varname">ip_addr</code>
with optional <code class="varname">key_id</code> and/or
<code class="varname">ip_port</code>.
A <code class="varname">masters_list</code> may include other
<code class="varname">masters_lists</code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">domain_name</code>
</p>
</td>
<td>
<p>
A quoted string which will be used as
a DNS name, for example "<code class="literal">my.test.domain</code>".
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">namelist</code>
</p>
</td>
<td>
<p>
A list of one or more <code class="varname">domain_name</code>
elements.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">dotted_decimal</code>
</p>
</td>
<td>
<p>
One to four integers valued 0 through
255 separated by dots (`.'), such as <span class="command"><strong>123</strong></span>,
<span class="command"><strong>45.67</strong></span> or <span class="command"><strong>89.123.45.67</strong></span>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">ip4_addr</code>
</p>
</td>
<td>
<p>
An IPv4 address with exactly four elements
in <code class="varname">dotted_decimal</code> notation.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">ip6_addr</code>
</p>
</td>
<td>
<p>
An IPv6 address, such as <span class="command"><strong>2001:db8::1234</strong></span>.
IPv6 scoped addresses that have ambiguity on their
scope zones must be disambiguated by an appropriate
zone ID with the percent character (`%') as
delimiter. It is strongly recommended to use
string zone names rather than numeric identifiers,
in order to be robust against system configuration
changes. However, since there is no standard
mapping for such names and identifier values,
currently only interface names as link identifiers
are supported, assuming one-to-one mapping between
interfaces and links. For example, a link-local
address <span class="command"><strong>fe80::1</strong></span> on the link
attached to the interface <span class="command"><strong>ne0</strong></span>
can be specified as <span class="command"><strong>fe80::1%ne0</strong></span>.
Note that on most systems link-local addresses
always have the ambiguity, and need to be
disambiguated.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">ip_addr</code>
</p>
</td>
<td>
<p>
An <code class="varname">ip4_addr</code> or <code class="varname">ip6_addr</code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">ip_dscp</code>
</p>
</td>
<td>
<p>
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.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">ip_port</code>
</p>
</td>
<td>
<p>
An IP port <code class="varname">number</code>.
The <code class="varname">number</code> is limited to 0
through 65535, with values
below 1024 typically restricted to use by processes running
as root.
In some cases, an asterisk (`*') character can be used as a
placeholder to
select a random high-numbered port.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">ip_prefix</code>
</p>
</td>
<td>
<p>
An IP network specified as an <code class="varname">ip_addr</code>,
followed by a slash (`/') and then the number of bits in the
netmask.
Trailing zeros in a <code class="varname">ip_addr</code>
may omitted.
For example, <span class="command"><strong>127/8</strong></span> is the
network <span class="command"><strong>127.0.0.0</strong></span> with
netmask <span class="command"><strong>255.0.0.0</strong></span> and <span class="command"><strong>1.2.3.0/28</strong></span> is
network <span class="command"><strong>1.2.3.0</strong></span> with netmask <span class="command"><strong>255.255.255.240</strong></span>.
</p>
<p>
When specifying a prefix involving a IPv6 scoped address
the scope may be omitted. In that case the prefix will
match packets from any scope.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">key_id</code>
</p>
</td>
<td>
<p>
A <code class="varname">domain_name</code> representing
the name of a shared key, to be used for transaction
security.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">key_list</code>
</p>
</td>
<td>
<p>
A list of one or more
<code class="varname">key_id</code>s,
separated by semicolons and ending with a semicolon.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">number</code>
</p>
</td>
<td>
<p>
A non-negative 32-bit integer
(i.e., a number between 0 and 4294967295, inclusive).
Its acceptable value might be further
limited by the context in which it is used.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">fixedpoint</code>
</p>
</td>
<td>
<p>
A non-negative real number that can be specified to
the nearest one hundredth. Up to five digits can be
specified before a decimal point, and up to two
digits after, so the maximum value is 99999.99.
Acceptable values might be further limited by the
context in which it is used.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">path_name</code>
</p>
</td>
<td>
<p>
A quoted string which will be used as
a pathname, such as <code class="filename">zones/master/my.test.domain</code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">port_list</code>
</p>
</td>
<td>
<p>
A list of an <code class="varname">ip_port</code> or a port
range.
A port range is specified in the form of
<strong class="userinput"><code>range</code></strong> followed by
two <code class="varname">ip_port</code>s,
<code class="varname">port_low</code> and
<code class="varname">port_high</code>, which represents
port numbers from <code class="varname">port_low</code> through
<code class="varname">port_high</code>, inclusive.
<code class="varname">port_low</code> must not be larger than
<code class="varname">port_high</code>.
For example,
<strong class="userinput"><code>range 1024 65535</code></strong> represents
ports from 1024 through 65535.
In either case an asterisk (`*') character is not
allowed as a valid <code class="varname">ip_port</code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">size_spec</code>
</p>
</td>
<td>
<p>
A 64-bit unsigned integer, or the keywords
<strong class="userinput"><code>unlimited</code></strong> or
<strong class="userinput"><code>default</code></strong>.
</p>
<p>
Integers may take values
0 <= value <= 18446744073709551615, though
certain parameters
(such as <span class="command"><strong>max-journal-size</strong></span>) may
use a more limited range within these extremes.
In most cases, setting a value to 0 does not
literally mean zero; it means "undefined" or
"as big as possible", depending on the context.
See the explanations of particular parameters
that use <code class="varname">size_spec</code>
for details on how they interpret its use.
</p>
<p>
Numeric values can optionally be followed by a
scaling factor:
<strong class="userinput"><code>K</code></strong> or <strong class="userinput"><code>k</code></strong>
for kilobytes,
<strong class="userinput"><code>M</code></strong> or <strong class="userinput"><code>m</code></strong>
for megabytes, and
<strong class="userinput"><code>G</code></strong> or <strong class="userinput"><code>g</code></strong>
for gigabytes, which scale by 1024, 1024*1024, and
1024*1024*1024 respectively.
</p>
<p>
<code class="varname">unlimited</code> generally means
"as big as possible", and is usually the best
way to safely set a very large number.
</p>
<p>
<code class="varname">default</code>
uses the limit that was in force when the server was started.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">size_or_percent</code>
</p>
</td>
<td>
<p>
<code class="varname">size_spec</code> or integer value
followed by '%' to represent percents.
</p>
<p>
The behavior is exactly the same as
<code class="varname">size_spec</code>, but
<code class="varname">size_or_percent</code> allows also
to specify a positive integer value followed by
'%' sign to represent percents.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">yes_or_no</code>
</p>
</td>
<td>
<p>
Either <strong class="userinput"><code>yes</code></strong> or <strong class="userinput"><code>no</code></strong>.
The words <strong class="userinput"><code>true</code></strong> and <strong class="userinput"><code>false</code></strong> are
also accepted, as are the numbers <strong class="userinput"><code>1</code></strong>
and <strong class="userinput"><code>0</code></strong>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">dialup_option</code>
</p>
</td>
<td>
<p>
One of <strong class="userinput"><code>yes</code></strong>,
<strong class="userinput"><code>no</code></strong>, <strong class="userinput"><code>notify</code></strong>,
<strong class="userinput"><code>notify-passive</code></strong>, <strong class="userinput"><code>refresh</code></strong> or
<strong class="userinput"><code>passive</code></strong>.
When used in a zone, <strong class="userinput"><code>notify-passive</code></strong>,
<strong class="userinput"><code>refresh</code></strong>, and <strong class="userinput"><code>passive</code></strong>
are restricted to slave and stub zones.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="address_match_lists"></a>Address Match Lists</h3></div></div></div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.7.4.4.2"></a>Syntax</h4></div></div></div>
<pre class="programlisting"><em class="replaceable"><code>address_match_list</code></em> = <em class="replaceable"><code>address_match_list_element</code></em> <span class="command"><strong>;</strong></span> ...
<em class="replaceable"><code>address_match_list_element</code></em> = [ <span class="command"><strong>!</strong></span> ] ( <em class="replaceable"><code>ip_address</code></em> | <em class="replaceable"><code>ip_prefix</code></em> |
<span class="command"><strong>key</strong></span> <em class="replaceable"><code>key_id</code></em> | <em class="replaceable"><code>acl_name</code></em> | <span class="command"><strong>{</strong></span> <em class="replaceable"><code>address_match_list</code></em> <span class="command"><strong>}</strong></span> )
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.7.4.4.3"></a>Definition and Usage</h4></div></div></div>
<p>
Address match lists are primarily used to determine access
control for various server operations. They are also used in
the <span class="command"><strong>listen-on</strong></span> and <span class="command"><strong>sortlist</strong></span>
statements. The elements which constitute an address match
list can be any of the following:
</p>
<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 <span class="command"><strong>key</strong></span>
statement
</li>
<li class="listitem">
the name of an address match list defined with
the <span class="command"><strong>acl</strong></span> statement
</li>
<li class="listitem">
a nested address match list enclosed in braces
</li>
</ul></div>
<p>
Elements can be negated with a leading exclamation mark (`!'),
and the match list names "any", "none", "localhost", and
"localnets" are predefined. More information on those names
can be found in the description of the acl statement.
</p>
<p>
The addition of the key clause made the name of this syntactic
element something of a misnomer, since security keys can be used
to validate access without regard to a host or network address.
Nonetheless, the term "address match list" is still used
throughout the documentation.
</p>
<p>
When a given IP address or prefix is compared to an address
match list, the comparison takes place in approximately O(1)
time. However, key comparisons require that the list of keys
be traversed until a matching key is found, and therefore may
be somewhat slower.
</p>
<p>
The interpretation of a match depends on whether the list is being
used for access control, defining <span class="command"><strong>listen-on</strong></span> ports, or in a
<span class="command"><strong>sortlist</strong></span>, and whether the element was negated.
</p>
<p>
When used as an access control list, a non-negated match
allows access and a negated match denies access. If
there is no match, access is denied. The clauses
<span class="command"><strong>allow-notify</strong></span>,
<span class="command"><strong>allow-recursion</strong></span>,
<span class="command"><strong>allow-recursion-on</strong></span>,
<span class="command"><strong>allow-query</strong></span>,
<span class="command"><strong>allow-query-on</strong></span>,
<span class="command"><strong>allow-query-cache</strong></span>,
<span class="command"><strong>allow-query-cache-on</strong></span>,
<span class="command"><strong>allow-transfer</strong></span>,
<span class="command"><strong>allow-update</strong></span>,
<span class="command"><strong>allow-update-forwarding</strong></span>,
<span class="command"><strong>blackhole</strong></span>, and
<span class="command"><strong>keep-response-order</strong></span> all use address match
lists. Similarly, the <span class="command"><strong>listen-on</strong></span> option will cause the
server to refuse queries on any of the machine's
addresses which do not match the list.
</p>
<p>
Order of insertion is significant. If more than one element
in an ACL is found to match a given IP address or prefix,
preference will be given to the one that came
<span class="emphasis"><em>first</em></span> in the ACL definition.
Because of this first-match behavior, an element that
defines a subset of another element in the list should
come before the broader element, regardless of whether
either is negated. For example, in
<span class="command"><strong>1.2.3/24; ! 1.2.3.13;</strong></span>
the 1.2.3.13 element is completely useless because the
algorithm will match any lookup for 1.2.3.13 to the 1.2.3/24
element. Using <span class="command"><strong>! 1.2.3.13; 1.2.3/24</strong></span> fixes
that problem by having 1.2.3.13 blocked by the negation, but
all other 1.2.3.* hosts fall through.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="comment_syntax"></a>Comment Syntax</h3></div></div></div>
<p>
The <acronym class="acronym">BIND</acronym> 9 comment syntax allows for
comments to appear
anywhere that whitespace may appear in a <acronym class="acronym">BIND</acronym> configuration
file. To appeal to programmers of all kinds, they can be written
in the C, C++, or shell/perl style.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.7.4.5.3"></a>Syntax</h4></div></div></div>
<p>
</p>
<pre class="programlisting">/* This is a <acronym class="acronym">BIND</acronym> comment as in C */</pre>
<p>
</p>
<pre class="programlisting">// This is a <acronym class="acronym">BIND</acronym> comment as in C++</pre>
<p>
</p>
<pre class="programlisting"># This is a <acronym class="acronym">BIND</acronym> comment as in common UNIX shells
# and perl</pre>
<p>
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.7.4.5.4"></a>Definition and Usage</h4></div></div></div>
<p>
Comments may appear anywhere that whitespace may appear in
a <acronym class="acronym">BIND</acronym> configuration file.
</p>
<p>
C-style comments start with the two characters /* (slash,
star) and end with */ (star, slash). Because they are completely
delimited with these characters, they can be used to comment only
a portion of a line or to span multiple lines.
</p>
<p>
C-style comments cannot be nested. For example, the following
is not valid because the entire comment ends with the first */:
</p>
<p>
</p>
<pre class="programlisting">/* This is the start of a comment.
This is still part of the comment.
/* This is an incorrect attempt at nesting a comment. */
This is no longer in any comment. */
</pre>
<p>
</p>
<p>
C++-style comments start with the two characters // (slash,
slash) and continue to the end of the physical line. They cannot
be continued across multiple physical lines; to have one logical
comment span multiple lines, each line must use the // pair.
For example:
</p>
<p>
</p>
<pre class="programlisting">// This is the start of a comment. The next line
// is a new comment, even though it is logically
// part of the previous comment.
</pre>
<p>
</p>
<p>
Shell-style (or perl-style, if you prefer) comments start
with the character <code class="literal">#</code> (number sign)
and continue to the end of the
physical line, as in C++ comments.
For example:
</p>
<p>
</p>
<pre class="programlisting"># This is the start of a comment. The next line
# is a new comment, even though it is logically
# part of the previous comment.
</pre>
<p>
</p>
<div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Warning</h3>
<p>
You cannot use the semicolon (`;') character
to start a comment such as you would in a zone file. The
semicolon indicates the end of a configuration
statement.
</p>
</div>
</div>
</div>
</div>
<div class="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>
<p>
A <acronym class="acronym">BIND</acronym> 9 configuration consists of
statements and comments.
Statements end with a semicolon. Statements and comments are the
only elements that can appear without enclosing braces. Many
statements contain a block of sub-statements, which are also
terminated with a semicolon.
</p>
<p>
The following statements are supported:
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.336in" class="1">
<col width="3.778in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p><span class="command"><strong>acl</strong></span></p>
</td>
<td>
<p>
defines a named IP address
matching list, for access control and other uses.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>controls</strong></span></p>
</td>
<td>
<p>
declares control channels to be used
by the <span class="command"><strong>rndc</strong></span> utility.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>include</strong></span></p>
</td>
<td>
<p>
includes a file.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>key</strong></span></p>
</td>
<td>
<p>
specifies key information for use in
authentication and authorization using TSIG.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>logging</strong></span></p>
</td>
<td>
<p>
specifies what the server logs, and where
the log messages are sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>lwres</strong></span></p>
</td>
<td>
<p>
configures <span class="command"><strong>named</strong></span> to
also act as a light-weight resolver daemon (<span class="command"><strong>lwresd</strong></span>).
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>masters</strong></span></p>
</td>
<td>
<p>
defines a named masters list for
inclusion in stub and slave zones'
<span class="command"><strong>masters</strong></span> or
<span class="command"><strong>also-notify</strong></span> lists.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>options</strong></span></p>
</td>
<td>
<p>
controls global server configuration
options and sets defaults for other statements.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>server</strong></span></p>
</td>
<td>
<p>
sets certain configuration options on
a per-server basis.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>statistics-channels</strong></span></p>
</td>
<td>
<p>
declares communication channels to get access to
<span class="command"><strong>named</strong></span> statistics.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>trusted-keys</strong></span></p>
</td>
<td>
<p>
defines trusted DNSSEC keys.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>managed-keys</strong></span></p>
</td>
<td>
<p>
lists DNSSEC keys to be kept up to date
using RFC 5011 trust anchor maintenance.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>view</strong></span></p>
</td>
<td>
<p>
defines a view.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>zone</strong></span></p>
</td>
<td>
<p>
defines a zone.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
The <span class="command"><strong>logging</strong></span> and
<span class="command"><strong>options</strong></span> statements may only occur once
per
configuration.
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="acl_grammar"></a><span class="command"><strong>acl</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting">
<span class="command"><strong>acl</strong></span> <em class="replaceable"><code>string</code></em> { <em class="replaceable"><code>address_match_element</code></em>; ... };
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="acl"></a><span class="command"><strong>acl</strong></span> Statement Definition and
Usage</h3></div></div></div>
<p>
The <span class="command"><strong>acl</strong></span> statement assigns a symbolic
name to an address match list. It gets its name from a primary
use of address match lists: Access Control Lists (ACLs).
</p>
<p>
The following ACLs are built-in:
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.130in" class="1">
<col width="4.000in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p><span class="command"><strong>any</strong></span></p>
</td>
<td>
<p>
Matches all hosts.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>none</strong></span></p>
</td>
<td>
<p>
Matches no hosts.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>localhost</strong></span></p>
</td>
<td>
<p>
Matches the IPv4 and IPv6 addresses of all network
interfaces on the system. When addresses are
added or removed, the <span class="command"><strong>localhost</strong></span>
ACL element is updated to reflect the changes.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>localnets</strong></span></p>
</td>
<td>
<p>
Matches any host on an IPv4 or IPv6 network
for which the system has an interface.
When addresses are added or removed,
the <span class="command"><strong>localnets</strong></span>
ACL element is updated to reflect the changes.
Some systems do not provide a way to determine the prefix
lengths of
local IPv6 addresses.
In such a case, <span class="command"><strong>localnets</strong></span>
only matches the local
IPv6 addresses, just like <span class="command"><strong>localhost</strong></span>.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="controls_grammar"></a><span class="command"><strong>controls</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting">
<span class="command"><strong>controls</strong></span> {
<span class="command"><strong>inet</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | <em class="replaceable"><code>ipv6_address</code></em> |
* ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] allow
{ <em class="replaceable"><code>address_match_element</code></em>; ... } [
<span class="command"><strong>keys</strong></span> { <em class="replaceable"><code>string</code></em>; ... } ] [ read-only
<em class="replaceable"><code>boolean</code></em> ];
<span class="command"><strong>unix</strong></span> <em class="replaceable"><code>quoted_string</code></em> perm <em class="replaceable"><code>integer</code></em>
<span class="command"><strong>owner</strong></span> <em class="replaceable"><code>integer</code></em> group <em class="replaceable"><code>integer</code></em> [
<span class="command"><strong>keys</strong></span> { <em class="replaceable"><code>string</code></em>; ... } ] [ read-only
<em class="replaceable"><code>boolean</code></em> ];
};
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="controls_statement_definition_and_usage"></a><span class="command"><strong>controls</strong></span> Statement Definition and
Usage</h3></div></div></div>
<p>
The <span class="command"><strong>controls</strong></span> statement declares control
channels to be used by system administrators to control the
operation of the name server. These control channels are
used by the <span class="command"><strong>rndc</strong></span> utility to send
commands to and retrieve non-DNS results from a name server.
</p>
<p>
An <span class="command"><strong>inet</strong></span> control channel is a TCP socket
listening at the specified <span class="command"><strong>ip_port</strong></span> on the
specified <span class="command"><strong>ip_addr</strong></span>, which can be an IPv4 or IPv6
address. An <span class="command"><strong>ip_addr</strong></span> of <code class="literal">*</code> (asterisk) is
interpreted as the IPv4 wildcard address; connections will be
accepted on any of the system's IPv4 addresses.
To listen on the IPv6 wildcard address,
use an <span class="command"><strong>ip_addr</strong></span> of <code class="literal">::</code>.
If you will only use <span class="command"><strong>rndc</strong></span> on the local host,
using the loopback address (<code class="literal">127.0.0.1</code>
or <code class="literal">::1</code>) is recommended for maximum security.
</p>
<p>
If no port is specified, port 953 is used. The asterisk
"<code class="literal">*</code>" cannot be used for <span class="command"><strong>ip_port</strong></span>.
</p>
<p>
The ability to issue commands over the control channel is
restricted by the <span class="command"><strong>allow</strong></span> and
<span class="command"><strong>keys</strong></span> clauses.
Connections to the control channel are permitted based on the
<span class="command"><strong>address_match_list</strong></span>. This is for simple
IP address based filtering only; any <span class="command"><strong>key_id</strong></span>
elements of the <span class="command"><strong>address_match_list</strong></span>
are ignored.
</p>
<p>
A <span class="command"><strong>unix</strong></span> control channel is a UNIX domain
socket listening at the specified path in the file system.
Access to the socket is specified by the <span class="command"><strong>perm</strong></span>,
<span class="command"><strong>owner</strong></span> and <span class="command"><strong>group</strong></span> clauses.
Note on some platforms (SunOS and Solaris) the permissions
(<span class="command"><strong>perm</strong></span>) are applied to the parent directory
as the permissions on the socket itself are ignored.
</p>
<p>
The primary authorization mechanism of the command
channel is the <span class="command"><strong>key_list</strong></span>, which
contains a list of <span class="command"><strong>key_id</strong></span>s.
Each <span class="command"><strong>key_id</strong></span> in the <span class="command"><strong>key_list</strong></span>
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 “Administrative Tools”</a>)
for information about configuring keys in <span class="command"><strong>rndc</strong></span>.
</p>
<p>
If the <span class="command"><strong>read-only</strong></span> clause is enabled, the
control channel is limited to the following set of read-only
commands: <span class="command"><strong>nta -dump</strong></span>,
<span class="command"><strong>null</strong></span>, <span class="command"><strong>status</strong></span>,
<span class="command"><strong>showzone</strong></span>, <span class="command"><strong>testgen</strong></span>, and
<span class="command"><strong>zonestatus</strong></span>. By default,
<span class="command"><strong>read-only</strong></span> is not enabled and the control
channel allows read-write access.
</p>
<p>
If no <span class="command"><strong>controls</strong></span> statement is present,
<span class="command"><strong>named</strong></span> will set up a default
control channel listening on the loopback address 127.0.0.1
and its IPv6 counterpart ::1.
In this case, and also when the <span class="command"><strong>controls</strong></span> statement
is present but does not have a <span class="command"><strong>keys</strong></span> clause,
<span class="command"><strong>named</strong></span> will attempt to load the command channel key
from the file <code class="filename">rndc.key</code> in
<code class="filename">/etc</code> (or whatever <code class="varname">sysconfdir</code>
was specified as when <acronym class="acronym">BIND</acronym> was built).
To create a <code class="filename">rndc.key</code> file, run
<strong class="userinput"><code>rndc-confgen -a</code></strong>.
</p>
<p>
The <code class="filename">rndc.key</code> feature was created to
ease the transition of systems from <acronym class="acronym">BIND</acronym> 8,
which did not have digital signatures on its command channel
messages and thus did not have a <span class="command"><strong>keys</strong></span> clause.
It makes it possible to use an existing <acronym class="acronym">BIND</acronym> 8
configuration file in <acronym class="acronym">BIND</acronym> 9 unchanged,
and still have <span class="command"><strong>rndc</strong></span> work the same way
<span class="command"><strong>ndc</strong></span> worked in BIND 8, simply by executing the
command <strong class="userinput"><code>rndc-confgen -a</code></strong> after BIND 9 is
installed.
</p>
<p>
Since the <code class="filename">rndc.key</code> feature
is only intended to allow the backward-compatible usage of
<acronym class="acronym">BIND</acronym> 8 configuration files, this
feature does not
have a high degree of configurability. You cannot easily change
the key name or the size of the secret, so you should make a
<code class="filename">rndc.conf</code> with your own key if you
wish to change
those things. The <code class="filename">rndc.key</code> file
also has its
permissions set such that only the owner of the file (the user that
<span class="command"><strong>named</strong></span> is running as) can access it.
If you
desire greater flexibility in allowing other users to access
<span class="command"><strong>rndc</strong></span> commands, then you need to create
a
<code class="filename">rndc.conf</code> file and make it group
readable by a group
that contains the users who should have access.
</p>
<p>
To disable the command channel, use an empty
<span class="command"><strong>controls</strong></span> statement:
<span class="command"><strong>controls { };</strong></span>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="include_grammar"></a><span class="command"><strong>include</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span class="command"><strong>include</strong></span> <em class="replaceable"><code>filename</code></em><span class="command"><strong>;</strong></span></pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="include_statement"></a><span class="command"><strong>include</strong></span> Statement Definition and Usage</h3></div></div></div>
<p>
The <span class="command"><strong>include</strong></span> statement inserts the
specified file at the point where the <span class="command"><strong>include</strong></span>
statement is encountered. The <span class="command"><strong>include</strong></span>
statement facilitates the administration of configuration
files
by permitting the reading or writing of some things but not
others. For example, the statement could include private keys
that are readable only by the name server.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="key_grammar"></a><span class="command"><strong>key</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting">
<span class="command"><strong>key</strong></span> <em class="replaceable"><code>string</code></em> {
<span class="command"><strong>algorithm</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>secret</strong></span> <em class="replaceable"><code>string</code></em>;
};
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="key_statement"></a><span class="command"><strong>key</strong></span> Statement Definition and Usage</h3></div></div></div>
<p>
The <span class="command"><strong>key</strong></span> statement defines a shared
secret key for use with TSIG (see <a class="xref" href="Bv9ARM.ch04.html#tsig" title="TSIG">the section called “TSIG”</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 “<span class="command"><strong>controls</strong></span> Statement Definition and
Usage”</a>).
</p>
<p>
The <span class="command"><strong>key</strong></span> statement can occur at the
top level
of the configuration file or inside a <span class="command"><strong>view</strong></span>
statement. Keys defined in top-level <span class="command"><strong>key</strong></span>
statements can be used in all views. Keys intended for use in
a <span class="command"><strong>controls</strong></span> statement
(see <a class="xref" href="Bv9ARM.ch06.html#controls_statement_definition_and_usage" title="controls Statement Definition and Usage">the section called “<span class="command"><strong>controls</strong></span> Statement Definition and
Usage”</a>)
must be defined at the top level.
</p>
<p>
The <em class="replaceable"><code>key_id</code></em>, also known as the
key name, is a domain name uniquely identifying the key. It can
be used in a <span class="command"><strong>server</strong></span>
statement to cause requests sent to that
server to be signed with this key, or in address match lists to
verify that incoming requests have been signed with a key
matching this name, algorithm, and secret.
</p>
<p>
The <em class="replaceable"><code>algorithm_id</code></em> is a string
that specifies a security/authentication algorithm. The
<span class="command"><strong>named</strong></span> 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
<em class="replaceable"><code>secret_string</code></em> is the secret
to be used by the algorithm, and is treated as a Base64
encoded string.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="logging_grammar"></a><span class="command"><strong>logging</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting">
<span class="command"><strong>logging</strong></span> {
<span class="command"><strong>category</strong></span> <em class="replaceable"><code>string</code></em> { <em class="replaceable"><code>string</code></em>; ... };
<span class="command"><strong>channel</strong></span> <em class="replaceable"><code>string</code></em> {
<span class="command"><strong>buffered</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>file</strong></span> <em class="replaceable"><code>quoted_string</code></em> [ versions ( "unlimited" | <em class="replaceable"><code>integer</code></em> )
] [ size <em class="replaceable"><code>size</code></em> ];
<span class="command"><strong>null</strong></span>;
<span class="command"><strong>print-category</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>print-severity</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>print-time</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>severity</strong></span> <em class="replaceable"><code>log_severity</code></em>;
<span class="command"><strong>stderr</strong></span>;
<span class="command"><strong>syslog</strong></span> [ <em class="replaceable"><code>syslog_facility</code></em> ];
};
};
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="logging_statement"></a><span class="command"><strong>logging</strong></span> Statement Definition and Usage</h3></div></div></div>
<p>
The <span class="command"><strong>logging</strong></span> statement configures a
wide
variety of logging options for the name server. Its <span class="command"><strong>channel</strong></span> phrase
associates output methods, format options and severity levels with
a name that can then be used with the <span class="command"><strong>category</strong></span> phrase
to select how various classes of messages are logged.
</p>
<p>
Only one <span class="command"><strong>logging</strong></span> statement is used to
define
as many channels and categories as are wanted. If there is no <span class="command"><strong>logging</strong></span> statement,
the logging configuration will be:
</p>
<pre class="programlisting">logging {
category default { default_syslog; default_debug; };
category unmatched { null; };
};
</pre>
<p>
If <span class="command"><strong>named</strong></span> is started with the
<code class="option">-L</code> option, it logs to the specified file
at startup, instead of using syslog. In this case the logging
configuration will be:
</p>
<pre class="programlisting">logging {
category default { default_logfile; default_debug; };
category unmatched { null; };
};
</pre>
<p>
In <acronym class="acronym">BIND</acronym> 9, the logging configuration
is only established when
the entire configuration file has been parsed. In <acronym class="acronym">BIND</acronym> 8, it was
established as soon as the <span class="command"><strong>logging</strong></span>
statement
was parsed. When the server is starting up, all logging messages
regarding syntax errors in the configuration file go to the default
channels, or to standard error if the <code class="option">-g</code> option
was specified.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="channel"></a>The <span class="command"><strong>channel</strong></span> Phrase</h4></div></div></div>
<p>
All log output goes to one or more <span class="emphasis"><em>channels</em></span>;
you can make as many of them as you want.
</p>
<p>
Every channel definition must include a destination clause that
says whether messages selected for the channel go to a file, to a
particular syslog facility, to the standard error stream, or are
discarded. It can optionally also limit the message severity level
that will be accepted by the channel (the default is
<span class="command"><strong>info</strong></span>), and whether to include a
<span class="command"><strong>named</strong></span>-generated time stamp, the
category name
and/or severity level (the default is not to include any).
</p>
<p>
The <span class="command"><strong>null</strong></span> destination clause
causes all messages sent to the channel to be discarded;
in that case, other options for the channel are meaningless.
</p>
<p>
The <span class="command"><strong>file</strong></span> destination clause directs
the channel
to a disk file. It can include limitations
both on how large the file is allowed to become, and how many
versions
of the file will be saved each time the file is opened.
</p>
<p>
If you use the <span class="command"><strong>versions</strong></span> log file
option, then
<span class="command"><strong>named</strong></span> will retain that many backup
versions of the file by
renaming them when opening. For example, if you choose to keep
three old versions
of the file <code class="filename">lamers.log</code>, then just
before it is opened
<code class="filename">lamers.log.1</code> is renamed to
<code class="filename">lamers.log.2</code>, <code class="filename">lamers.log.0</code> is renamed
to <code class="filename">lamers.log.1</code>, and <code class="filename">lamers.log</code> is
renamed to <code class="filename">lamers.log.0</code>.
You can say <span class="command"><strong>versions unlimited</strong></span> to
not limit
the number of versions.
If a <span class="command"><strong>size</strong></span> option is associated with
the log file,
then renaming is only done when the file being opened exceeds the
indicated size. No backup versions are kept by default; any
existing
log file is simply appended.
</p>
<p>
The <span class="command"><strong>size</strong></span> option for files is used
to limit log
growth. If the file ever exceeds the size, then <span class="command"><strong>named</strong></span> will
stop writing to the file unless it has a <span class="command"><strong>versions</strong></span> option
associated with it. If backup versions are kept, the files are
rolled as
described above and a new one begun. If there is no
<span class="command"><strong>versions</strong></span> option, no more data will
be written to the log
until some out-of-band mechanism removes or truncates the log to
less than the
maximum size. The default behavior is not to limit the size of
the
file.
</p>
<p>
Example usage of the <span class="command"><strong>size</strong></span> and
<span class="command"><strong>versions</strong></span> options:
</p>
<pre class="programlisting">channel an_example_channel {
file "example.log" versions 3 size 20m;
print-time yes;
print-category yes;
};
</pre>
<p>
The <span class="command"><strong>syslog</strong></span> destination clause
directs the
channel to the system log. Its argument is a
syslog facility as described in the <span class="command"><strong>syslog</strong></span> man
page. Known facilities are <span class="command"><strong>kern</strong></span>, <span class="command"><strong>user</strong></span>,
<span class="command"><strong>mail</strong></span>, <span class="command"><strong>daemon</strong></span>, <span class="command"><strong>auth</strong></span>,
<span class="command"><strong>syslog</strong></span>, <span class="command"><strong>lpr</strong></span>, <span class="command"><strong>news</strong></span>,
<span class="command"><strong>uucp</strong></span>, <span class="command"><strong>cron</strong></span>, <span class="command"><strong>authpriv</strong></span>,
<span class="command"><strong>ftp</strong></span>, <span class="command"><strong>local0</strong></span>, <span class="command"><strong>local1</strong></span>,
<span class="command"><strong>local2</strong></span>, <span class="command"><strong>local3</strong></span>, <span class="command"><strong>local4</strong></span>,
<span class="command"><strong>local5</strong></span>, <span class="command"><strong>local6</strong></span> and
<span class="command"><strong>local7</strong></span>, however not all facilities
are supported on
all operating systems.
How <span class="command"><strong>syslog</strong></span> will handle messages
sent to
this facility is described in the <span class="command"><strong>syslog.conf</strong></span> man
page. If you have a system which uses a very old version of <span class="command"><strong>syslog</strong></span> that
only uses two arguments to the <span class="command"><strong>openlog()</strong></span> function,
then this clause is silently ignored.
</p>
<p>
On Windows machines syslog messages are directed to the EventViewer.
</p>
<p>
The <span class="command"><strong>severity</strong></span> clause works like <span class="command"><strong>syslog</strong></span>'s
"priorities", except that they can also be used if you are writing
straight to a file rather than using <span class="command"><strong>syslog</strong></span>.
Messages which are not at least of the severity level given will
not be selected for the channel; messages of higher severity
levels
will be accepted.
</p>
<p>
If you are using <span class="command"><strong>syslog</strong></span>, then the <span class="command"><strong>syslog.conf</strong></span> priorities
will also determine what eventually passes through. For example,
defining a channel facility and severity as <span class="command"><strong>daemon</strong></span> and <span class="command"><strong>debug</strong></span> but
only logging <span class="command"><strong>daemon.warning</strong></span> via <span class="command"><strong>syslog.conf</strong></span> will
cause messages of severity <span class="command"><strong>info</strong></span> and
<span class="command"><strong>notice</strong></span> to
be dropped. If the situation were reversed, with <span class="command"><strong>named</strong></span> writing
messages of only <span class="command"><strong>warning</strong></span> or higher,
then <span class="command"><strong>syslogd</strong></span> would
print all messages it received from the channel.
</p>
<p>
The <span class="command"><strong>stderr</strong></span> destination clause
directs the
channel to the server's standard error stream. This is intended
for
use when the server is running as a foreground process, for
example
when debugging a configuration.
</p>
<p>
The server can supply extensive debugging information when
it is in debugging mode. If the server's global debug level is
greater
than zero, then debugging mode will be active. The global debug
level is set either by starting the <span class="command"><strong>named</strong></span> server
with the <code class="option">-d</code> flag followed by a positive integer,
or by running <span class="command"><strong>rndc trace</strong></span>.
The global debug level
can be set to zero, and debugging mode turned off, by running <span class="command"><strong>rndc
notrace</strong></span>. All debugging messages in the server have a debug
level, and higher debug levels give more detailed output. Channels
that specify a specific debug severity, for example:
</p>
<pre class="programlisting">channel specific_debug_level {
file "foo";
severity debug 3;
};
</pre>
<p>
will get debugging output of level 3 or less any time the
server is in debugging mode, regardless of the global debugging
level. Channels with <span class="command"><strong>dynamic</strong></span>
severity use the
server's global debug level to determine what messages to print.
</p>
<p>
If <span class="command"><strong>print-time</strong></span> has been turned on,
then
the date and time will be logged. <span class="command"><strong>print-time</strong></span> may
be specified for a <span class="command"><strong>syslog</strong></span> channel,
but is usually
pointless since <span class="command"><strong>syslog</strong></span> also logs
the date and
time. If <span class="command"><strong>print-category</strong></span> is
requested, then the
category of the message will be logged as well. Finally, if <span class="command"><strong>print-severity</strong></span> is
on, then the severity level of the message will be logged. The <span class="command"><strong>print-</strong></span> options may
be used in any combination, and will always be printed in the
following
order: time, category, severity. Here is an example where all
three <span class="command"><strong>print-</strong></span> options
are on:
</p>
<p>
<code class="computeroutput">28-Feb-2000 15:05:32.863 general: notice: running</code>
</p>
<p>
If <span class="command"><strong>buffered</strong></span> has been turned on the output
to files will not be flushed after each log entry. By default
all log messages are flushed.
</p>
<p>
There are four predefined channels that are used for
<span class="command"><strong>named</strong></span>'s default logging as follows.
If <span class="command"><strong>named</strong></span> is started with the
<code class="option">-L</code> then a
fifth channel <span class="command"><strong>default_logfile</strong></span> 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 “The <span class="command"><strong>category</strong></span> Phrase”</a>.
</p>
<pre class="programlisting">channel default_syslog {
// send to syslog's daemon facility
syslog daemon;
// only send priority info and higher
severity info;
};
channel default_debug {
// write to named.run in the working directory
// Note: stderr is used instead of "named.run" if
// the server is started with the '-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>
<p>
The <span class="command"><strong>default_debug</strong></span> channel has the
special
property that it only produces output when the server's debug
level is
nonzero. It normally writes to a file called <code class="filename">named.run</code>
in the server's working directory.
</p>
<p>
For security reasons, when the <code class="option">-u</code>
command line option is used, the <code class="filename">named.run</code> file
is created only after <span class="command"><strong>named</strong></span> has
changed to the
new UID, and any debug output generated while <span class="command"><strong>named</strong></span> is
starting up and still running as root is discarded. If you need
to capture this output, you must run the server with the <code class="option">-L</code>
option to specify a default logfile, or the <code class="option">-g</code>
option to log to standard error which you can redirect to a file.
</p>
<p>
Once a channel is defined, it cannot be redefined. Thus you
cannot alter the built-in channels directly, but you can modify
the default logging by pointing categories at channels you have
defined.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="the_category_phrase"></a>The <span class="command"><strong>category</strong></span> Phrase</h4></div></div></div>
<p>
There are many categories, so you can send the logs you want
to see wherever you want, without seeing logs you don't want. If
you don't specify a list of channels for a category, then log
messages
in that category will be sent to the <span class="command"><strong>default</strong></span> category
instead. If you don't specify a default category, the following
"default default" is used:
</p>
<pre class="programlisting">category default { default_syslog; default_debug; };
</pre>
<p>
If you start <span class="command"><strong>named</strong></span> with the
<code class="option">-L</code> option then the default category is:
</p>
<pre class="programlisting">category default { default_logfile; default_debug; };
</pre>
<p>
As an example, let's say you want to log security events to
a file, but you also want keep the default logging behavior. You'd
specify the following:
</p>
<pre class="programlisting">channel my_security_channel {
file "my_security_file";
severity info;
};
category security {
my_security_channel;
default_syslog;
default_debug;
};</pre>
<p>
To discard all messages in a category, specify the <span class="command"><strong>null</strong></span> channel:
</p>
<pre class="programlisting">category xfer-out { null; };
category notify { null; };
</pre>
<p>
Following are the available categories and brief descriptions
of the types of log information they contain. More
categories may be added in future <acronym class="acronym">BIND</acronym> releases.
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.150in" class="1">
<col width="3.350in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p><span class="command"><strong>client</strong></span></p>
</td>
<td>
<p>
Processing of client requests.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>cname</strong></span></p>
</td>
<td>
<p>
Logs nameservers that are skipped due to them being
a CNAME rather than A / AAAA records.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>config</strong></span></p>
</td>
<td>
<p>
Configuration file parsing and processing.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>database</strong></span></p>
</td>
<td>
<p>
Messages relating to the databases used
internally by the name server to store zone and cache
data.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>default</strong></span></p>
</td>
<td>
<p>
The default category defines the logging
options for those categories where no specific
configuration has been
defined.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>delegation-only</strong></span></p>
</td>
<td>
<p>
Delegation only. Logs queries that have been
forced to NXDOMAIN as the result of a
delegation-only zone or a
<span class="command"><strong>delegation-only</strong></span> in a
forward, hint or stub zone declaration.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>dispatch</strong></span></p>
</td>
<td>
<p>
Dispatching of incoming packets to the
server modules where they are to be processed.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>dnssec</strong></span></p>
</td>
<td>
<p>
DNSSEC and TSIG protocol processing.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>dnstap</strong></span></p>
</td>
<td>
<p>
The "dnstap" DNS traffic capture system.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>edns-disabled</strong></span></p>
</td>
<td>
<p>
Log queries that have been forced to use plain
DNS due to timeouts. This is often due to
the remote servers not being RFC 1034 compliant
(not always returning FORMERR or similar to
EDNS queries and other extensions to the DNS
when they are not understood). In other words, this is
targeted at servers that fail to respond to
DNS queries that they don't understand.
</p>
<p>
Note: the log message can also be due to
packet loss. Before reporting servers for
non-RFC 1034 compliance they should be re-tested
to determine the nature of the non-compliance.
This testing should prevent or reduce the
number of false-positive reports.
</p>
<p>
Note: eventually <span class="command"><strong>named</strong></span> will have to stop
treating such timeouts as due to RFC 1034 non
compliance and start treating it as plain
packet loss. Falsely classifying packet
loss as due to RFC 1034 non compliance impacts
on DNSSEC validation which requires EDNS for
the DNSSEC records to be returned.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>general</strong></span></p>
</td>
<td>
<p>
The catch-all. Many things still aren't
classified into categories, and they all end up here.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>lame-servers</strong></span></p>
</td>
<td>
<p>
Lame servers. These are misconfigurations
in remote servers, discovered by BIND 9 when trying to
query those servers during resolution.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>network</strong></span></p>
</td>
<td>
<p>
Network operations.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>notify</strong></span></p>
</td>
<td>
<p>
The NOTIFY protocol.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>queries</strong></span></p>
</td>
<td>
<p>
Specify where queries should be logged to.
</p>
<p>
At startup, specifying the category <span class="command"><strong>queries</strong></span> will also
enable query logging unless <span class="command"><strong>querylog</strong></span> option has been
specified.
</p>
<p>
The query log entry first reports a client object
identifier in @0x<hexadecimal-number>
format. Next, it reports the client's IP
address and port number, and the query name,
class and type. Next, it reports whether the
Recursion Desired flag was set (+ if set, -
if not set), if the query was signed (S),
EDNS was in used along with the EDNS version
number (E(#)), if TCP was used (T), if DO
(DNSSEC Ok) was set (D), if CD (Checking
Disabled) was set (C), if a valid DNS Server
COOKIE was received (V), or if a DNS COOKIE
option without a valid Server COOKIE was
present (K). After this the destination
address the query was sent to is reported.
</p>
<p>
<code class="computeroutput">client 127.0.0.1#62536 (www.example.com): query: www.example.com IN AAAA +SE</code>
</p>
<p>
<code class="computeroutput">client ::1#62537 (www.example.net): query: www.example.net IN AAAA -SE</code>
</p>
<p>
(The first part of this log message, showing the
client address/port number and query name, is
repeated in all subsequent log messages related
to the same query.)
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>query-errors</strong></span></p>
</td>
<td>
<p>
Information about queries that resulted in some
failure.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>rate-limit</strong></span></p>
</td>
<td>
<p>
The start, periodic, and final notices of the
rate limiting of a stream of responses are logged at
<span class="command"><strong>info</strong></span> severity in this category.
These messages include a hash value of the domain name
of the response and the name itself,
except when there is insufficient memory to record
the name for the final notice
The final notice is normally delayed until about one
minute after rate limit stops.
A lack of memory can hurry the final notice,
in which case it starts with an asterisk (*).
Various internal events are logged at debug 1 level
and higher.
</p>
<p>
Rate limiting of individual requests
is logged in the <span class="command"><strong>query-errors</strong></span> category.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>resolver</strong></span></p>
</td>
<td>
<p>
DNS resolution, such as the recursive
lookups performed on behalf of clients by a caching name
server.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>rpz</strong></span></p>
</td>
<td>
<p>
Information about errors in response policy zone files,
rewritten responses, and at the highest
<span class="command"><strong>debug</strong></span> levels, mere rewriting
attempts.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>security</strong></span></p>
</td>
<td>
<p>
Approval and denial of requests.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>spill</strong></span></p>
</td>
<td>
<p>
Logs queries that have been terminated, either by dropping
or responding with SERVFAIL, as a result of a fetchlimit
quota being exceeded.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>trust-anchor-telemetry</strong></span></p>
</td>
<td>
<p>
Logs trust-anchor-telemetry requests received by named.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>unmatched</strong></span></p>
</td>
<td>
<p>
Messages that <span class="command"><strong>named</strong></span> was unable to determine the
class of or for which there was no matching <span class="command"><strong>view</strong></span>.
A one line summary is also logged to the <span class="command"><strong>client</strong></span> category.
This category is best sent to a file or stderr, by
default it is sent to
the <span class="command"><strong>null</strong></span> channel.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>update</strong></span></p>
</td>
<td>
<p>
Dynamic updates.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>update-security</strong></span></p>
</td>
<td>
<p>
Approval and denial of update requests.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>xfer-in</strong></span></p>
</td>
<td>
<p>
Zone transfers the server is receiving.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>xfer-out</strong></span></p>
</td>
<td>
<p>
Zone transfers the server is sending.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="query_errors"></a>The <span class="command"><strong>query-errors</strong></span> Category</h4></div></div></div>
<p>
The <span class="command"><strong>query-errors</strong></span> category is
specifically intended for debugging purposes: To identify
why and how specific queries result in responses which
indicate an error.
Messages of this category are therefore only logged
with <span class="command"><strong>debug</strong></span> levels.
</p>
<p>
At the debug levels of 1 or higher, each response with the
rcode of SERVFAIL is logged as follows:
</p>
<p>
<code class="computeroutput">client 127.0.0.1#61502: query failed (SERVFAIL) for www.example.com/IN/AAAA at query.c:3880</code>
</p>
<p>
This means an error resulting in SERVFAIL was
detected at line 3880 of source file
<code class="filename">query.c</code>.
Log messages of this level will particularly
help identify the cause of SERVFAIL for an
authoritative server.
</p>
<p>
At the debug levels of 2 or higher, detailed context
information of recursive resolutions that resulted in
SERVFAIL is logged.
The log message will look like as follows:
</p>
<p>
</p>
<pre class="programlisting">
fetch completed at resolver.c:2970 for www.example.com/A
in 30.000183: timed out/success [domain:example.com,
referral:2,restart:7,qrysent:8,timeout:5,lame:0,neterr:0,
badresp:1,adberr:0,findfail:0,valfail:0]
</pre>
<p>
</p>
<p>
The first part before the colon shows that a recursive
resolution for AAAA records of www.example.com completed
in 30.000183 seconds and the final result that led to the
SERVFAIL was determined at line 2970 of source file
<code class="filename">resolver.c</code>.
</p>
<p>
The following part shows the detected final result and the
latest result of DNSSEC validation.
The latter is always success when no validation attempt
is made.
In this example, this query resulted in SERVFAIL probably
because all name servers are down or unreachable, leading
to a timeout in 30 seconds.
DNSSEC validation was probably not attempted.
</p>
<p>
The last part enclosed in square brackets shows statistics
information collected for this particular resolution
attempt.
The <code class="varname">domain</code> field shows the deepest zone
that the resolver reached;
it is the zone where the error was finally detected.
The meaning of the other fields is summarized in the
following table.
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.150in" class="1">
<col width="3.350in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p><code class="varname">referral</code></p>
</td>
<td>
<p>
The number of referrals the resolver received
throughout the resolution process.
In the above example this is 2, which are most
likely com and example.com.
</p>
</td>
</tr>
<tr>
<td>
<p><code class="varname">restart</code></p>
</td>
<td>
<p>
The number of cycles that the resolver tried
remote servers at the <code class="varname">domain</code>
zone.
In each cycle the resolver sends one query
(possibly resending it, depending on the response)
to each known name server of
the <code class="varname">domain</code> zone.
</p>
</td>
</tr>
<tr>
<td>
<p><code class="varname">qrysent</code></p>
</td>
<td>
<p>
The number of queries the resolver sent at the
<code class="varname">domain</code> zone.
</p>
</td>
</tr>
<tr>
<td>
<p><code class="varname">timeout</code></p>
</td>
<td>
<p>
The number of timeouts since the resolver
received the last response.
</p>
</td>
</tr>
<tr>
<td>
<p><code class="varname">lame</code></p>
</td>
<td>
<p>
The number of lame servers the resolver detected
at the <code class="varname">domain</code> zone.
A server is detected to be lame either by an
invalid response or as a result of lookup in
BIND9's address database (ADB), where lame
servers are cached.
</p>
</td>
</tr>
<tr>
<td>
<p><code class="varname">neterr</code></p>
</td>
<td>
<p>
The number of erroneous results that the
resolver encountered in sending queries
at the <code class="varname">domain</code> zone.
One common case is the remote server is
unreachable and the resolver receives an ICMP
unreachable error message.
</p>
</td>
</tr>
<tr>
<td>
<p><code class="varname">badresp</code></p>
</td>
<td>
<p>
The number of unexpected responses (other than
<code class="varname">lame</code>) to queries sent by the
resolver at the <code class="varname">domain</code> zone.
</p>
</td>
</tr>
<tr>
<td>
<p><code class="varname">adberr</code></p>
</td>
<td>
<p>
Failures in finding remote server addresses
of the <code class="varname">domain</code> zone in the ADB.
One common case of this is that the remote
server's name does not have any address records.
</p>
</td>
</tr>
<tr>
<td>
<p><code class="varname">findfail</code></p>
</td>
<td>
<p>
Failures of resolving remote server addresses.
This is a total number of failures throughout
the resolution process.
</p>
</td>
</tr>
<tr>
<td>
<p><code class="varname">valfail</code></p>
</td>
<td>
<p>
Failures of DNSSEC validation.
Validation failures are counted throughout
the resolution process (not limited to
the <code class="varname">domain</code> zone), but should
only happen in <code class="varname">domain</code>.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
At the debug levels of 3 or higher, the same messages
as those at the debug 1 level are logged for other errors
than SERVFAIL.
Note that negative responses such as NXDOMAIN are not
regarded as errors here.
</p>
<p>
At the debug levels of 4 or higher, the same messages
as those at the debug 2 level are logged for other errors
than SERVFAIL.
Unlike the above case of level 3, messages are logged for
negative responses.
This is because any unexpected results can be difficult to
debug in the recursion case.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="lwres_grammar"></a><span class="command"><strong>lwres</strong></span> Statement Grammar</h3></div></div></div>
<p>
This is the grammar of the <span class="command"><strong>lwres</strong></span>
statement in the <code class="filename">named.conf</code> file:
</p>
<pre class="programlisting"><span class="command"><strong>lwres {</strong></span>
[ <span class="command"><strong>listen-on {</strong></span>
( <em class="replaceable"><code>ip_addr</code></em> [ <span class="command"><strong>port</strong></span> <em class="replaceable"><code>ip_port</code></em> ] [ <span class="command"><strong>dscp</strong></span> <em class="replaceable"><code>ip_dscp</code></em> ] <span class="command"><strong>;</strong></span> )
...
<span class="command"><strong>};</strong></span> ]
[ <span class="command"><strong>view</strong></span> <em class="replaceable"><code>view_name</code></em><span class="command"><strong>;</strong></span> ]
[ <span class="command"><strong>search {</strong></span> <em class="replaceable"><code>domain_name</code></em> <span class="command"><strong>;</strong></span> ... <span class="command"><strong>};</strong></span> ]
[ <span class="command"><strong>ndots</strong></span> <em class="replaceable"><code>number</code></em><span class="command"><strong>;</strong></span> ]
[ <span class="command"><strong>lwres-tasks</strong></span> <em class="replaceable"><code>number</code></em><span class="command"><strong>;</strong></span> ]
[ <span class="command"><strong>lwres-clients</strong></span> <em class="replaceable"><code>number</code></em><span class="command"><strong>;</strong></span> ]
<span class="command"><strong>};</strong></span>
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="lwres_statement"></a><span class="command"><strong>lwres</strong></span> Statement Definition and Usage</h3></div></div></div>
<p>
The <span class="command"><strong>lwres</strong></span> 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 “Running a Resolver Daemon”</a>.) There may be multiple
<span class="command"><strong>lwres</strong></span> statements configuring
lightweight resolver servers with different properties.
</p>
<p>
The <span class="command"><strong>listen-on</strong></span> statement specifies a
list of
IPv4 addresses (and ports) that this instance of a lightweight
resolver daemon
should accept requests on. If no port is specified, port 921 is
used.
If this statement is omitted, requests will be accepted on
127.0.0.1,
port 921.
</p>
<p>
The <span class="command"><strong>view</strong></span> statement binds this
instance of a
lightweight resolver daemon to a view in the DNS namespace, so that
the
response will be constructed in the same manner as a normal DNS
query
matching this view. If this statement is omitted, the default view
is
used, and if there is no default view, an error is triggered.
</p>
<p>
The <span class="command"><strong>search</strong></span> statement is equivalent to
the
<span class="command"><strong>search</strong></span> statement in
<code class="filename">/etc/resolv.conf</code>. It provides a
list of domains
which are appended to relative names in queries.
</p>
<p>
The <span class="command"><strong>ndots</strong></span> statement is equivalent to
the
<span class="command"><strong>ndots</strong></span> statement in
<code class="filename">/etc/resolv.conf</code>. It indicates the
minimum
number of dots in a relative domain name that should result in an
exact match lookup before search path elements are appended.
</p>
<p>
The <code class="option">lwres-tasks</code> statement specifies the number
of worker threads the lightweight resolver will dedicate to serving
clients. By default the number is the same as the number of CPUs on
the system; this can be overridden using the <code class="option">-n</code>
command line option when starting the server.
</p>
<p>
The <code class="option">lwres-clients</code> specifies
the number of client objects per thread the lightweight
resolver should create to serve client queries.
By default, if the lightweight resolver runs as a part
of <span class="command"><strong>named</strong></span>, 256 client objects are
created for each task; if it runs as <span class="command"><strong>lwresd</strong></span>,
1024 client objects are created for each thread. The maximum
value is 32768; higher values will be silently ignored and
the maximum will be used instead.
Note that setting too high a value may overconsume
system resources.
</p>
<p>
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>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="masters_grammar"></a><span class="command"><strong>masters</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting">
<span class="command"><strong>masters</strong></span> <em class="replaceable"><code>string</code></em> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp
<em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>masters</code></em> | <em class="replaceable"><code>ipv4_address</code></em> [
<span class="command"><strong>port</strong></span> <em class="replaceable"><code>integer</code></em> ] | <em class="replaceable"><code>ipv6_address</code></em> [ port
<em class="replaceable"><code>integer</code></em> ] ) [ key <em class="replaceable"><code>string</code></em> ]; ... };
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="masters_statement"></a><span class="command"><strong>masters</strong></span> Statement Definition and
Usage</h3></div></div></div>
<p><span class="command"><strong>masters</strong></span>
lists allow for a common set of masters to be easily used by
multiple stub and slave zones in their <span class="command"><strong>masters</strong></span>
or <span class="command"><strong>also-notify</strong></span> lists.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="options_grammar"></a><span class="command"><strong>options</strong></span> Statement Grammar</h3></div></div></div>
<p>
This is the grammar of the <span class="command"><strong>options</strong></span>
statement in the <code class="filename">named.conf</code> file:
</p>
<pre class="programlisting">
<span class="command"><strong>options</strong></span> {
<span class="command"><strong>acache-cleaning-interval</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>acache-enable</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>additional-from-auth</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>additional-from-cache</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>allow-new-zones</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>allow-notify</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-query</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-query-cache</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-query-cache-on</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-query-on</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-recursion</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-recursion-on</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-transfer</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-update</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-update-forwarding</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>also-notify</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>masters</code></em> |
<em class="replaceable"><code>ipv4_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] | <em class="replaceable"><code>ipv6_address</code></em> [ port
<em class="replaceable"><code>integer</code></em> ] ) [ key <em class="replaceable"><code>string</code></em> ]; ... };
<span class="command"><strong>alt-transfer-source</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * )
] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>alt-transfer-source-v6</strong></span> ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> |
* ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>answer-cookie</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>attach-cache</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>auth-nxdomain</strong></span> <em class="replaceable"><code>boolean</code></em>; // default changed
<span class="command"><strong>auto-dnssec</strong></span> ( allow | maintain | off );
<span class="command"><strong>automatic-interface-scan</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>avoid-v4-udp-ports</strong></span> { <em class="replaceable"><code>portrange</code></em>; ... };
<span class="command"><strong>avoid-v6-udp-ports</strong></span> { <em class="replaceable"><code>portrange</code></em>; ... };
<span class="command"><strong>bindkeys-file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>blackhole</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>cache-file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>catalog-zones</strong></span> { zone <em class="replaceable"><code>quoted_string</code></em> [ default-masters [ port
<em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>masters</code></em> | <em class="replaceable"><code>ipv4_address</code></em> [
<span class="command"><strong>port</strong></span> <em class="replaceable"><code>integer</code></em> ] | <em class="replaceable"><code>ipv6_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] ) [ key
<em class="replaceable"><code>string</code></em> ]; ... } ] [ zone-directory <em class="replaceable"><code>quoted_string</code></em> ] [
<span class="command"><strong>in-memory</strong></span> <em class="replaceable"><code>boolean</code></em> ] [ min-update-interval <em class="replaceable"><code>integer</code></em> ]; ... };
<span class="command"><strong>check-dup-records</strong></span> ( fail | warn | ignore );
<span class="command"><strong>check-integrity</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>check-mx</strong></span> ( fail | warn | ignore );
<span class="command"><strong>check-mx-cname</strong></span> ( fail | warn | ignore );
<span class="command"><strong>check-names</strong></span> ( master | slave | response
) ( fail | warn | ignore );
<span class="command"><strong>check-sibling</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>check-spf</strong></span> ( warn | ignore );
<span class="command"><strong>check-srv-cname</strong></span> ( fail | warn | ignore );
<span class="command"><strong>check-wildcard</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>cleaning-interval</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>clients-per-query</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>cookie-algorithm</strong></span> ( aes | sha1 | sha256 );
<span class="command"><strong>cookie-secret</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>coresize</strong></span> ( default | unlimited | <em class="replaceable"><code>sizeval</code></em> );
<span class="command"><strong>datasize</strong></span> ( default | unlimited | <em class="replaceable"><code>sizeval</code></em> );
<span class="command"><strong>deny-answer-addresses</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... } [
<span class="command"><strong>except-from</strong></span> { <em class="replaceable"><code>quoted_string</code></em>; ... } ];
<span class="command"><strong>deny-answer-aliases</strong></span> { <em class="replaceable"><code>quoted_string</code></em>; ... } [ except-from {
<em class="replaceable"><code>quoted_string</code></em>; ... } ];
<span class="command"><strong>dialup</strong></span> ( notify | notify-passive | passive | refresh | <em class="replaceable"><code>boolean</code></em> );
<span class="command"><strong>directory</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>disable-algorithms</strong></span> <em class="replaceable"><code>string</code></em> { <em class="replaceable"><code>string</code></em>;
... };
<span class="command"><strong>disable-ds-digests</strong></span> <em class="replaceable"><code>string</code></em> { <em class="replaceable"><code>string</code></em>;
... };
<span class="command"><strong>disable-empty-zone</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>dns64</strong></span> <em class="replaceable"><code>netprefix</code></em> {
<span class="command"><strong>break-dnssec</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>clients</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>exclude</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>mapped</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>recursive-only</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>suffix</strong></span> <em class="replaceable"><code>ipv6_address</code></em>;
};
<span class="command"><strong>dns64-contact</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>dns64-server</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>dnssec-accept-expired</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>dnssec-dnskey-kskonly</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>dnssec-enable</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>dnssec-loadkeys-interval</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>dnssec-lookaside</strong></span> ( <em class="replaceable"><code>string</code></em> trust-anchor
<em class="replaceable"><code>string</code></em> | auto | no );
<span class="command"><strong>dnssec-must-be-secure</strong></span> <em class="replaceable"><code>string</code></em> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>dnssec-secure-to-insecure</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>dnssec-update-mode</strong></span> ( maintain | no-resign );
<span class="command"><strong>dnssec-validation</strong></span> ( yes | no | auto );
<span class="command"><strong>dnstap</strong></span> { ( all | auth | client | forwarder |
<span class="command"><strong>resolver</strong></span> ) [ ( query | response ) ]; ... };
<span class="command"><strong>dnstap-identity</strong></span> ( <em class="replaceable"><code>quoted_string</code></em> | none |
<span class="command"><strong>hostname</strong></span> );
<span class="command"><strong>dnstap-output</strong></span> ( file | unix ) <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>dnstap-version</strong></span> ( <em class="replaceable"><code>quoted_string</code></em> | none );
<span class="command"><strong>dscp</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>dual-stack-servers</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>quoted_string</code></em> [ port
<em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] | <em class="replaceable"><code>ipv4_address</code></em> [ port
<em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] | <em class="replaceable"><code>ipv6_address</code></em> [ port
<em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] ); ... };
<span class="command"><strong>dump-file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>edns-udp-size</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>empty-contact</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>empty-server</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>empty-zones-enable</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>fetch-quota-params</strong></span> <em class="replaceable"><code>integer</code></em> <em class="replaceable"><code>fixedpoint</code></em> <em class="replaceable"><code>fixedpoint</code></em> <em class="replaceable"><code>fixedpoint</code></em>;
<span class="command"><strong>fetches-per-server</strong></span> <em class="replaceable"><code>integer</code></em> [ ( drop | fail ) ];
<span class="command"><strong>fetches-per-zone</strong></span> <em class="replaceable"><code>integer</code></em> [ ( drop | fail ) ];
<span class="command"><strong>files</strong></span> ( default | unlimited | <em class="replaceable"><code>sizeval</code></em> );
<span class="command"><strong>filter-aaaa</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>filter-aaaa-on-v4</strong></span> ( break-dnssec | <em class="replaceable"><code>boolean</code></em> );
<span class="command"><strong>filter-aaaa-on-v6</strong></span> ( break-dnssec | <em class="replaceable"><code>boolean</code></em> );
<span class="command"><strong>flush-zones-on-shutdown</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>forward</strong></span> ( first | only );
<span class="command"><strong>forwarders</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>ipv4_address</code></em>
| <em class="replaceable"><code>ipv6_address</code></em> ) [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ]; ... };
<span class="command"><strong>fstrm-set-buffer-hint</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>fstrm-set-flush-timeout</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>fstrm-set-input-queue-size</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>fstrm-set-output-notify-threshold</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>fstrm-set-output-queue-model</strong></span> ( mpsc | spsc );
<span class="command"><strong>fstrm-set-output-queue-size</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>fstrm-set-reopen-interval</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>geoip-directory</strong></span> ( <em class="replaceable"><code>quoted_string</code></em> | none );
<span class="command"><strong>geoip-use-ecs</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>heartbeat-interval</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>hostname</strong></span> ( <em class="replaceable"><code>quoted_string</code></em> | none );
<span class="command"><strong>inline-signing</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>interface-interval</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>ixfr-from-differences</strong></span> ( master | slave | <em class="replaceable"><code>boolean</code></em> );
<span class="command"><strong>keep-response-order</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>key-directory</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>lame-ttl</strong></span> <em class="replaceable"><code>ttlval</code></em>;
<span class="command"><strong>listen-on</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp
<em class="replaceable"><code>integer</code></em> ] {
<em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>listen-on-v6</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp
<em class="replaceable"><code>integer</code></em> ] {
<em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>lmdb-mapsize</strong></span> <em class="replaceable"><code>sizeval</code></em>;
<span class="command"><strong>lock-file</strong></span> ( <em class="replaceable"><code>quoted_string</code></em> | none );
<span class="command"><strong>managed-keys-directory</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>masterfile-format</strong></span> ( map | raw | text );
<span class="command"><strong>masterfile-style</strong></span> ( full | relative );
<span class="command"><strong>match-mapped-addresses</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>max-acache-size</strong></span> ( unlimited | <em class="replaceable"><code>sizeval</code></em> );
<span class="command"><strong>max-cache-size</strong></span> ( default | unlimited | <em class="replaceable"><code>sizeval</code></em> | <em class="replaceable"><code>percentage</code></em> );
<span class="command"><strong>max-cache-ttl</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-clients-per-query</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-journal-size</strong></span> ( unlimited | <em class="replaceable"><code>sizeval</code></em> );
<span class="command"><strong>max-ncache-ttl</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-records</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-recursion-depth</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-recursion-queries</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-refresh-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-retry-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-rsa-exponent-size</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-idle-in</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-idle-out</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-time-in</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-time-out</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-udp-size</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-zone-ttl</strong></span> ( unlimited | <em class="replaceable"><code>ttlval</code></em> );
<span class="command"><strong>memstatistics</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>memstatistics-file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>message-compression</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>min-refresh-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>min-retry-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>minimal-any</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>minimal-responses</strong></span> ( no-auth | no-auth-recursive | <em class="replaceable"><code>boolean</code></em> );
<span class="command"><strong>multi-master</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>no-case-compress</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>nocookie-udp-size</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>notify</strong></span> ( explicit | master-only | <em class="replaceable"><code>boolean</code></em> );
<span class="command"><strong>notify-delay</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>notify-rate</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>notify-source</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [
<span class="command"><strong>dscp</strong></span> <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>notify-source-v6</strong></span> ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ]
[ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>notify-to-soa</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>nta-lifetime</strong></span> <em class="replaceable"><code>ttlval</code></em>;
<span class="command"><strong>nta-recheck</strong></span> <em class="replaceable"><code>ttlval</code></em>;
<span class="command"><strong>nxdomain-redirect</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>pid-file</strong></span> ( <em class="replaceable"><code>quoted_string</code></em> | none );
<span class="command"><strong>port</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>preferred-glue</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>prefetch</strong></span> <em class="replaceable"><code>integer</code></em> [ <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>provide-ixfr</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>query-source</strong></span> ( ( [ address ] ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port (
<em class="replaceable"><code>integer</code></em> | * ) ] ) | ( [ [ address ] ( <em class="replaceable"><code>ipv4_address</code></em> | * ) ]
<span class="command"><strong>port</strong></span> ( <em class="replaceable"><code>integer</code></em> | * ) ) ) [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>query-source-v6</strong></span> ( ( [ address ] ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port (
<em class="replaceable"><code>integer</code></em> | * ) ] ) | ( [ [ address ] ( <em class="replaceable"><code>ipv6_address</code></em> | * ) ]
<span class="command"><strong>port</strong></span> ( <em class="replaceable"><code>integer</code></em> | * ) ) ) [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>querylog</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>random-device</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>rate-limit</strong></span> {
<span class="command"><strong>all-per-second</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>errors-per-second</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>exempt-clients</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>ipv4-prefix-length</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>ipv6-prefix-length</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>log-only</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>max-table-size</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>min-table-size</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>nodata-per-second</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>nxdomains-per-second</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>qps-scale</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>referrals-per-second</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>responses-per-second</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>slip</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>window</strong></span> <em class="replaceable"><code>integer</code></em>;
};
<span class="command"><strong>recursing-file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>recursion</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>recursive-clients</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>request-expire</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>request-ixfr</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>request-nsid</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>require-server-cookie</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>reserved-sockets</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>resolver-query-timeout</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>response-policy</strong></span> { zone <em class="replaceable"><code>quoted_string</code></em> [ log <em class="replaceable"><code>boolean</code></em> ] [
<span class="command"><strong>max-policy-ttl</strong></span> <em class="replaceable"><code>integer</code></em> ] [ policy ( cname | disabled | drop |
<span class="command"><strong>given</strong></span> | no-op | nodata | nxdomain | passthru | tcp-only
<em class="replaceable"><code>quoted_string</code></em> ) ] [ recursive-only <em class="replaceable"><code>boolean</code></em> ]; ... } [
<span class="command"><strong>break-dnssec</strong></span> <em class="replaceable"><code>boolean</code></em> ] [ max-policy-ttl <em class="replaceable"><code>integer</code></em> ] [
<span class="command"><strong>min-ns-dots</strong></span> <em class="replaceable"><code>integer</code></em> ] [ nsip-wait-recurse <em class="replaceable"><code>boolean</code></em> ] [
<span class="command"><strong>qname-wait-recurse</strong></span> <em class="replaceable"><code>boolean</code></em> ] [ recursive-only <em class="replaceable"><code>boolean</code></em> ];
<span class="command"><strong>root-delegation-only</strong></span> [ exclude { <em class="replaceable"><code>quoted_string</code></em>; ... } ];
<span class="command"><strong>root-key-sentinel</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>rrset-order</strong></span> { [ class <em class="replaceable"><code>string</code></em> ] [ type <em class="replaceable"><code>string</code></em> ] [ name
<em class="replaceable"><code>quoted_string</code></em> ] <em class="replaceable"><code>string</code></em> <em class="replaceable"><code>string</code></em>; ... };
<span class="command"><strong>secroots-file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>send-cookie</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>serial-query-rate</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>serial-update-method</strong></span> ( date | increment | unixtime );
<span class="command"><strong>server-id</strong></span> ( <em class="replaceable"><code>quoted_string</code></em> | none | hostname );
<span class="command"><strong>servfail-ttl</strong></span> <em class="replaceable"><code>ttlval</code></em>;
<span class="command"><strong>session-keyalg</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>session-keyfile</strong></span> ( <em class="replaceable"><code>quoted_string</code></em> | none );
<span class="command"><strong>session-keyname</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>sig-signing-nodes</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>sig-signing-signatures</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>sig-signing-type</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>sig-validity-interval</strong></span> <em class="replaceable"><code>integer</code></em> [ <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>sortlist</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>stacksize</strong></span> ( default | unlimited | <em class="replaceable"><code>sizeval</code></em> );
<span class="command"><strong>startup-notify-rate</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>statistics-file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>tcp-clients</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>tcp-listen-queue</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>tkey-dhkey</strong></span> <em class="replaceable"><code>quoted_string</code></em> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>tkey-domain</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>tkey-gssapi-credential</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>tkey-gssapi-keytab</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>transfer-format</strong></span> ( many-answers | one-answer );
<span class="command"><strong>transfer-message-size</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>transfer-source</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [
<span class="command"><strong>dscp</strong></span> <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>transfer-source-v6</strong></span> ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * )
] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>transfers-in</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>transfers-out</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>transfers-per-ns</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>trust-anchor-telemetry</strong></span> <em class="replaceable"><code>boolean</code></em>; // experimental
<span class="command"><strong>try-tcp-refresh</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>update-check-ksk</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>use-alt-transfer-source</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>use-v4-udp-ports</strong></span> { <em class="replaceable"><code>portrange</code></em>; ... };
<span class="command"><strong>use-v6-udp-ports</strong></span> { <em class="replaceable"><code>portrange</code></em>; ... };
<span class="command"><strong>v6-bias</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>version</strong></span> ( <em class="replaceable"><code>quoted_string</code></em> | none );
<span class="command"><strong>zero-no-soa-ttl</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>zero-no-soa-ttl-cache</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>zone-statistics</strong></span> ( full | terse | none | <em class="replaceable"><code>boolean</code></em> );
};
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="options"></a><span class="command"><strong>options</strong></span> Statement Definition and
Usage</h3></div></div></div>
<p>
The <span class="command"><strong>options</strong></span> statement sets up global
options
to be used by <acronym class="acronym">BIND</acronym>. This statement
may appear only
once in a configuration file. If there is no <span class="command"><strong>options</strong></span>
statement, an options block with each option set to its default will
be used.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>attach-cache</strong></span></span></dt>
<dd>
<p>
Allows multiple views to share a single cache
database.
Each view has its own cache database by default, but
if multiple views have the same operational policy
for name resolution and caching, those views can
share a single cache to save memory and possibly
improve resolution efficiency by using this option.
</p>
<p>
The <span class="command"><strong>attach-cache</strong></span> option
may also be specified in <span class="command"><strong>view</strong></span>
statements, in which case it overrides the
global <span class="command"><strong>attach-cache</strong></span> option.
</p>
<p>
The <em class="replaceable"><code>cache_name</code></em> specifies
the cache to be shared.
When the <span class="command"><strong>named</strong></span> server configures
views which are supposed to share a cache, it
creates a cache with the specified name for the
first view of these sharing views.
The rest of the views will simply refer to the
already created cache.
</p>
<p>
One common configuration to share a cache would be to
allow all views to share a single cache.
This can be done by specifying
the <span class="command"><strong>attach-cache</strong></span> as a global
option with an arbitrary name.
</p>
<p>
Another possible operation is to allow a subset of
all views to share a cache while the others to
retain their own caches.
For example, if there are three views A, B, and C,
and only A and B should share a cache, specify the
<span class="command"><strong>attach-cache</strong></span> option as a view A (or
B)'s option, referring to the other view name:
</p>
<pre class="programlisting">
view "A" {
// this view has its own cache
...
};
view "B" {
// this view refers to A's cache
attach-cache "A";
};
view "C" {
// this view has its own cache
...
};
</pre>
<p>
Views that share a cache must have the same policy
on configurable parameters that may affect caching.
The current implementation requires the following
configurable options be consistent among these
views:
<span class="command"><strong>check-names</strong></span>,
<span class="command"><strong>cleaning-interval</strong></span>,
<span class="command"><strong>dnssec-accept-expired</strong></span>,
<span class="command"><strong>dnssec-validation</strong></span>,
<span class="command"><strong>max-cache-ttl</strong></span>,
<span class="command"><strong>max-ncache-ttl</strong></span>,
<span class="command"><strong>max-cache-size</strong></span>, and
<span class="command"><strong>zero-no-soa-ttl</strong></span>.
</p>
<p>
Note that there may be other parameters that may
cause confusion if they are inconsistent for
different views that share a single cache.
For example, if these views define different sets of
forwarders that can return different answers for the
same question, sharing the answer does not make
sense or could even be harmful.
It is administrator's responsibility to ensure
configuration differences in different views do
not cause disruption with a shared cache.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>directory</strong></span></span></dt>
<dd>
<p>
The working directory of the server.
Any non-absolute pathnames in the configuration file will
be taken as relative to this directory. The default
location for most server output files
(e.g. <code class="filename">named.run</code>) is this directory.
If a directory is not specified, the working directory
defaults to `<code class="filename">.</code>', the directory from
which the server was started. The directory specified
should be an absolute path. It is
<span class="emphasis"><em>strongly recommended</em></span>
that the directory be writable by the effective user
ID of the <span class="command"><strong>named</strong></span> process.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnstap</strong></span></span></dt>
<dd>
<p>
<span class="command"><strong>dnstap</strong></span> 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, <span class="command"><strong>dnstap</strong></span>
uses
<span class="command"><strong>libfstrm</strong></span> (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
(<span class="command"><strong>libprotobuf-c</strong></span>, 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>).
</p>
<p>
To enable <span class="command"><strong>dnstap</strong></span> at compile time,
the <span class="command"><strong>fstrm</strong></span> and <span class="command"><strong>protobuf-c</strong></span>
libraries must be available, and BIND must be configured with
<code class="option">--enable-dnstap</code>.
</p>
<p>
The <span class="command"><strong>dnstap</strong></span> option is a bracketed list
of message types to be logged. These may be set differently
for each view. Supported types are <code class="literal">client</code>,
<code class="literal">auth</code>, <code class="literal">resolver</code>, and
<code class="literal">forwarder</code>. Specifying type
<code class="literal">all</code> will cause all <span class="command"><strong>dnstap</strong></span>
messages to be logged, regardless of type.
</p>
<p>
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.
</p>
<p>
Example: To log all authoritative queries and responses,
recursive client responses, and upstream queries sent by
the resolver, use:
</p>
<pre class="programlisting">dnstap {
auth;
client response;
resolver query;
};
</pre>
<p>
</p>
<p>
Logged <span class="command"><strong>dnstap</strong></span> messages can be parsed
using the <span class="command"><strong>dnstap-read</strong></span> utility (see
<a class="xref" href="man.dnstap-read.html" title="dnstap-read"><span class="refentrytitle"><span class="application">dnstap-read</span></span>(1)</a> for details).
</p>
<p>
For more information on <span class="command"><strong>dnstap</strong></span>, see
<a class="link" href="http://dnstap.info" target="_top">http://dnstap.info</a>.
</p>
<p>
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:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<span class="command"><strong>fstrm-set-buffer-hint</strong></span>: 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">
<span class="command"><strong>fstrm-set-flush-timeout</strong></span>: 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">
<span class="command"><strong>fstrm-set-output-notify-threshold</strong></span>:
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">
<span class="command"><strong>fstrm-set-output-queue-model</strong></span>:
Controls the queuing semantics to use for queue
objects. The default is <code class="literal">mpsc</code>
(multiple producer, single consumer); the other
option is <code class="literal">spsc</code> (single producer,
single consumer).
</li>
<li class="listitem">
<span class="command"><strong>fstrm-set-input-queue-size</strong></span>: 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">
<span class="command"><strong>fstrm-set-output-queue-size</strong></span>:
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">
<span class="command"><strong>fstrm-set-reopen-interval</strong></span>:
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>
<p>
Note that all of the above minimum, maximum, and default
values are set by the <span class="command"><strong>libfstrm</strong></span> library,
and may be subject to change in future versions of the
library. See the <span class="command"><strong>libfstrm</strong></span> documentation
for more information.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnstap-output</strong></span></span></dt>
<dd>
<p>
Configures the path to which the <span class="command"><strong>dnstap</strong></span>
frame stream will be sent if <span class="command"><strong>dnstap</strong></span>
is enabled at compile time and active.
</p>
<p>
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, <span class="command"><strong>dnstap</strong></span> messages will
only be sent if another process such as
<span class="command"><strong>fstrm_capture</strong></span>
(provided with <span class="command"><strong>libfstrm</strong></span>) is listening on
the socket.)
</p>
<p>
<span class="command"><strong>dnstap-output</strong></span> can only be set globally
in <span class="command"><strong>options</strong></span>. Currently, it can only be
set once while <span class="command"><strong>named</strong></span> is running;
once set, it cannot be changed by
<span class="command"><strong>rndc reload</strong></span> or
<span class="command"><strong>rndc reconfig</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnstap-identity</strong></span></span></dt>
<dd>
<p>
Specifies an <span class="command"><strong>identity</strong></span> string to send in
<span class="command"><strong>dnstap</strong></span> messages. If set to
<code class="literal">hostname</code>, which is the default, the
server's hostname will be sent. If set to
<code class="literal">none</code>, no identity string will be sent.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnstap-version</strong></span></span></dt>
<dd>
<p>
Specifies a <span class="command"><strong>version</strong></span> string to send in
<span class="command"><strong>dnstap</strong></span> messages. The default is the
version number of the BIND release. If set to
<code class="literal">none</code>, no version string will be sent.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>geoip-directory</strong></span></span></dt>
<dd>
<p>
Specifies the directory containing GeoIP
<code class="filename">.dat</code> database files for GeoIP
initialization. By default, this option is unset
and the GeoIP support will use libGeoIP's
built-in directory.
(For details, see <a class="xref" href="Bv9ARM.ch06.html#acl" title="acl Statement Definition and Usage">the section called “<span class="command"><strong>acl</strong></span> Statement Definition and
Usage”</a> about the
<span class="command"><strong>geoip</strong></span> ACL.)
</p>
</dd>
<dt><span class="term"><span class="command"><strong>key-directory</strong></span></span></dt>
<dd>
<p>
When performing dynamic update of secure zones, the
directory where the public and private DNSSEC key files
should be found, if different than the current working
directory. (Note that this option has no effect on the
paths for files containing non-DNSSEC keys such as
<code class="filename">bind.keys</code>,
<code class="filename">rndc.key</code> or
<code class="filename">session.key</code>.)
</p>
</dd>
<dt><span class="term"><span class="command"><strong>lmdb-mapsize</strong></span></span></dt>
<dd>
<p>
When <span class="command"><strong>named</strong></span> 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 <span class="command"><strong>rndc addzone</strong></span>.
Note that this is not the NZD database file size, but
the largest size that the database may grow to.
</p>
<p>
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 <span class="command"><strong>named</strong></span> 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.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>managed-keys-directory</strong></span></span></dt>
<dd>
<p>
Specifies the directory in which to store the files that
track managed DNSSEC keys. By default, this is the working
directory. The directory <span class="emphasis"><em>must</em></span>
be writable by the effective user ID of the
<span class="command"><strong>named</strong></span> process.
</p>
<p>
If <span class="command"><strong>named</strong></span> is not configured to use views,
then managed keys for the server will be tracked in a single
file called <code class="filename">managed-keys.bind</code>.
Otherwise, managed keys will be tracked in separate files,
one file per view; each file name will be the 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>.
</p>
<p>
(Note: in previous releases, file names for views
always used the SHA256 hash of the view name. To ensure
compatibility after upgrade, if a file using the old
name format is found to exist, it will be used instead
of the new format.)
</p>
</dd>
<dt><span class="term"><span class="command"><strong>named-xfer</strong></span></span></dt>
<dd>
<p>
<span class="emphasis"><em>This option is obsolete.</em></span> It
was used in <acronym class="acronym">BIND</acronym> 8 to specify
the pathname to the <span class="command"><strong>named-xfer</strong></span>
program. In <acronym class="acronym">BIND</acronym> 9, no separate
<span class="command"><strong>named-xfer</strong></span> program is needed;
its functionality is built into the name server.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>tkey-gssapi-keytab</strong></span></span></dt>
<dd>
<p>
The KRB5 keytab file to use for GSS-TSIG updates. If
this option is set and tkey-gssapi-credential is not
set, then updates will be allowed with any key
matching a principal in the specified keytab.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>tkey-gssapi-credential</strong></span></span></dt>
<dd>
<p>
The security credential with which the server should
authenticate keys requested by the GSS-TSIG protocol.
Currently only Kerberos 5 authentication is available
and the credential is a Kerberos principal which the
server can acquire through the default system key
file, normally <code class="filename">/etc/krb5.keytab</code>.
The location keytab file can be overridden using the
tkey-gssapi-keytab option. Normally this principal is
of the form "<strong class="userinput"><code>DNS/</code></strong><code class="varname">server.domain</code>".
To use GSS-TSIG, <span class="command"><strong>tkey-domain</strong></span> must
also be set if a specific keytab is not set with
tkey-gssapi-keytab.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>tkey-domain</strong></span></span></dt>
<dd>
<p>
The domain appended to the names of all shared keys
generated with <span class="command"><strong>TKEY</strong></span>. When a
client requests a <span class="command"><strong>TKEY</strong></span> exchange,
it may or may not specify the desired name for the
key. If present, the name of the shared key will
be <code class="varname">client specified part</code> +
<code class="varname">tkey-domain</code>. Otherwise, the
name of the shared key will be <code class="varname">random hex
digits</code> + <code class="varname">tkey-domain</code>.
In most cases, the <span class="command"><strong>domainname</strong></span>
should be the server's domain name, or an otherwise
non-existent subdomain like
"_tkey.<code class="varname">domainname</code>". If you are
using GSS-TSIG, this variable must be defined, unless
you specify a specific keytab using tkey-gssapi-keytab.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>tkey-dhkey</strong></span></span></dt>
<dd>
<p>
The Diffie-Hellman key used by the server
to generate shared keys with clients using the Diffie-Hellman
mode
of <span class="command"><strong>TKEY</strong></span>. The server must be
able to load the
public and private keys from files in the working directory.
In
most cases, the <code class="varname">key_name</code> should be the server's host name.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>cache-file</strong></span></span></dt>
<dd>
<p>
This is for testing only. Do not use.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dump-file</strong></span></span></dt>
<dd>
<p>
The pathname of the file the server dumps
the database to when instructed to do so with
<span class="command"><strong>rndc dumpdb</strong></span>.
If not specified, the default is <code class="filename">named_dump.db</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>memstatistics-file</strong></span></span></dt>
<dd>
<p>
The pathname of the file the server writes memory
usage statistics to on exit. If not specified,
the default is <code class="filename">named.memstats</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>lock-file</strong></span></span></dt>
<dd>
<p>
The pathname of a file on which <span class="command"><strong>named</strong></span> will
attempt to acquire a file lock when starting up for
the first time; if unsuccessful, the server will
will terminate, under the assumption that another
server is already running. If not specified, the default is
<code class="filename">/var/run/named/named.lock</code>.
</p>
<p>
Specifying <span class="command"><strong>lock-file none</strong></span> disables the
use of a lock file. <span class="command"><strong>lock-file</strong></span> is
ignored if <span class="command"><strong>named</strong></span> was run using the <code class="option">-X</code>
option, which overrides it. Changes to
<span class="command"><strong>lock-file</strong></span> are ignored if
<span class="command"><strong>named</strong></span> is being reloaded or
reconfigured; it is only effective when the server is
first started up.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>pid-file</strong></span></span></dt>
<dd>
<p>
The pathname of the file the server writes its process ID
in. If not specified, the default is
<code class="filename">/var/run/named/named.pid</code>.
The PID file is used by programs that want to send signals to
the running
name server. Specifying <span class="command"><strong>pid-file none</strong></span> disables the
use of a PID file — no file will be written and any
existing one will be removed. Note that <span class="command"><strong>none</strong></span>
is a keyword, not a filename, and therefore is not enclosed
in
double quotes.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>recursing-file</strong></span></span></dt>
<dd>
<p>
The pathname of the file the server dumps
the queries that are currently recursing when instructed
to do so with <span class="command"><strong>rndc recursing</strong></span>.
If not specified, the default is <code class="filename">named.recursing</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>statistics-file</strong></span></span></dt>
<dd>
<p>
The pathname of the file the server appends statistics
to when instructed to do so using <span class="command"><strong>rndc stats</strong></span>.
If not specified, the default is <code class="filename">named.stats</code> in the
server's current directory. The format of the file is
described
in <a class="xref" href="Bv9ARM.ch06.html#statsfile" title="The Statistics File">the section called “The Statistics File”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>bindkeys-file</strong></span></span></dt>
<dd>
<p>
The pathname of a file to override the built-in trusted
keys provided by <span class="command"><strong>named</strong></span>.
See the discussion of <span class="command"><strong>dnssec-validation</strong></span>
for details. If not specified, the default is
<code class="filename">/etc/bind.keys</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>secroots-file</strong></span></span></dt>
<dd>
<p>
The pathname of the file the server dumps
security roots to when instructed to do so with
<span class="command"><strong>rndc secroots</strong></span>.
If not specified, the default is
<code class="filename">named.secroots</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>session-keyfile</strong></span></span></dt>
<dd>
<p>
The pathname of the file into which to write a TSIG
session key generated by <span class="command"><strong>named</strong></span> for use by
<span class="command"><strong>nsupdate -l</strong></span>. 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 “Dynamic Update Policies”</a>, and in
particular the discussion of the
<span class="command"><strong>update-policy</strong></span> statement's
<strong class="userinput"><code>local</code></strong> option for more
information about this feature.)
</p>
</dd>
<dt><span class="term"><span class="command"><strong>session-keyname</strong></span></span></dt>
<dd>
<p>
The key name to use for the TSIG session key.
If not specified, the default is "local-ddns".
</p>
</dd>
<dt><span class="term"><span class="command"><strong>session-keyalg</strong></span></span></dt>
<dd>
<p>
The algorithm to use for the TSIG session key.
Valid values are hmac-sha1, hmac-sha224, hmac-sha256,
hmac-sha384, hmac-sha512 and hmac-md5. If not
specified, the default is hmac-sha256.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>port</strong></span></span></dt>
<dd>
<p>
The UDP/TCP port number the server uses for
receiving and sending DNS protocol traffic.
The default is 53. This option is mainly intended for server
testing;
a server using a port other than 53 will not be able to
communicate with
the global DNS.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dscp</strong></span></span></dt>
<dd>
<p>
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.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>random-device</strong></span></span></dt>
<dd>
<p>
The source of entropy to be used by the server. Entropy is
primarily needed
for DNSSEC operations, such as TKEY transactions and dynamic
update of signed
zones. This options specifies the device (or file) from which
to read
entropy. If this is a file, operations requiring entropy will
fail when the
file has been exhausted. If not specified, the default value
is
<code class="filename">/dev/random</code>
(or equivalent) when present, and none otherwise. The
<span class="command"><strong>random-device</strong></span> option takes
effect during
the initial configuration load at server startup time and
is ignored on subsequent reloads.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>preferred-glue</strong></span></span></dt>
<dd>
<p>
If specified, the listed type (A or AAAA) will be emitted
before other glue
in the additional section of a query response.
The default is to prefer A records when responding
to queries that arrived via IPv4 and AAAA when
responding to queries that arrived via IPv6.
</p>
</dd>
<dt>
<a name="root_delegation_only"></a><span class="term"><span class="command"><strong>root-delegation-only</strong></span></span>
</dt>
<dd>
<p>
Turn on enforcement of delegation-only in TLDs
(top level domains) and root zones with an optional
exclude list.
</p>
<p>
DS queries are expected to be made to and be answered by
delegation only zones. Such queries and responses are
treated as an exception to delegation-only processing
and are not converted to NXDOMAIN responses provided
a CNAME is not discovered at the query name.
</p>
<p>
If a delegation only zone server also serves a child
zone it is not always possible to determine whether
an answer comes from the delegation only zone or the
child zone. SOA NS and DNSKEY records are apex
only records and a matching response that contains
these records or DS is treated as coming from a
child zone. RRSIG records are also examined to see
if they are signed by a child zone or not. The
authority section is also examined to see if there
is evidence that the answer is from the child zone.
Answers that are determined to be from a child zone
are not converted to NXDOMAIN responses. Despite
all these checks there is still a possibility of
false negatives when a child zone is being served.
</p>
<p>
Similarly false positives can arise from empty nodes
(no records at the name) in the delegation only zone
when the query type is not ANY.
</p>
<p>
Note some TLDs are not delegation only (e.g. "DE", "LV",
"US" and "MUSEUM"). This list is not exhaustive.
</p>
<pre class="programlisting">
options {
root-delegation-only exclude { "de"; "lv"; "us"; "museum"; };
};
</pre>
</dd>
<dt><span class="term"><span class="command"><strong>disable-algorithms</strong></span></span></dt>
<dd>
<p>
Disable the specified DNSSEC algorithms at and below the
specified name.
Multiple <span class="command"><strong>disable-algorithms</strong></span>
statements are allowed.
Only the best match <span class="command"><strong>disable-algorithms</strong></span>
clause will be used to determine which algorithms are used.
</p>
<p>
If all supported algorithms are disabled, the zones covered
by the <span class="command"><strong>disable-algorithms</strong></span> will be treated
as insecure.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>disable-ds-digests</strong></span></span></dt>
<dd>
<p>
Disable the specified DS/DLV digest types at and below the
specified name.
Multiple <span class="command"><strong>disable-ds-digests</strong></span>
statements are allowed.
Only the best match <span class="command"><strong>disable-ds-digests</strong></span>
clause will be used to determine which digest types are used.
</p>
<p>
If all supported digest types are disabled, the zones covered
by the <span class="command"><strong>disable-ds-digests</strong></span> will be treated
as insecure.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-lookaside</strong></span></span></dt>
<dd>
<p>
When set, <span class="command"><strong>dnssec-lookaside</strong></span> provides the
validator with an alternate method to validate DNSKEY
records at the top of a zone. When a DNSKEY is at or
below a domain specified by the deepest
<span class="command"><strong>dnssec-lookaside</strong></span>, and the normal DNSSEC
validation has left the key untrusted, the trust-anchor
will be appended to the key name and a DLV record will be
looked up to see if it can validate the key. If the DLV
record validates a DNSKEY (similarly to the way a DS
record does) the DNSKEY RRset is deemed to be trusted.
</p>
<p>
If <span class="command"><strong>dnssec-lookaside</strong></span> is set to
<strong class="userinput"><code>no</code></strong>, then dnssec-lookaside
is not used.
</p>
<p>
NOTE: The ISC-provided DLV service at
<code class="literal">dlv.isc.org</code>, has been shut down.
The <span class="command"><strong>dnssec-lookaside auto;</strong></span>
configuration option, which set <span class="command"><strong>named</strong></span>
up to use ISC DLV with minimal configuration, has
accordingly been removed.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-must-be-secure</strong></span></span></dt>
<dd>
<p>
Specify hierarchies which must be or may not be secure
(signed and validated). If <strong class="userinput"><code>yes</code></strong>,
then <span class="command"><strong>named</strong></span> will only accept answers if
they are secure. If <strong class="userinput"><code>no</code></strong>, then normal
DNSSEC validation applies allowing for insecure answers to
be accepted. The specified domain must be under a
<span class="command"><strong>trusted-keys</strong></span> or
<span class="command"><strong>managed-keys</strong></span> statement, or
<span class="command"><strong>dnssec-validation auto</strong></span> must be active.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dns64</strong></span></span></dt>
<dd>
<p>
This directive instructs <span class="command"><strong>named</strong></span> to
return mapped IPv4 addresses to AAAA queries when
there are no AAAA records. It is intended to be
used in conjunction with a NAT64. Each
<span class="command"><strong>dns64</strong></span> defines one DNS64 prefix.
Multiple DNS64 prefixes can be defined.
</p>
<p>
Compatible IPv6 prefixes have lengths of 32, 40, 48, 56,
64 and 96 as per RFC 6052.
</p>
<p>
Additionally a reverse IP6.ARPA zone will be created for
the prefix to provide a mapping from the IP6.ARPA names
to the corresponding IN-ADDR.ARPA names using synthesized
CNAMEs. <span class="command"><strong>dns64-server</strong></span> and
<span class="command"><strong>dns64-contact</strong></span> can be used to specify
the name of the server and contact for the zones. These
are settable at the view / options level. These are
not settable on a per-prefix basis.
</p>
<p>
Each <span class="command"><strong>dns64</strong></span> supports an optional
<span class="command"><strong>clients</strong></span> ACL that determines which
clients are affected by this directive. If not defined,
it defaults to <strong class="userinput"><code>any;</code></strong>.
</p>
<p>
Each <span class="command"><strong>dns64</strong></span> supports an optional
<span class="command"><strong>mapped</strong></span> ACL that selects which
IPv4 addresses are to be mapped in the corresponding
A RRset. If not defined it defaults to
<strong class="userinput"><code>any;</code></strong>.
</p>
<p>
Normally, DNS64 won't apply to a domain name that
owns one or more AAAA records; these records will
simply be returned. The optional
<span class="command"><strong>exclude</strong></span> ACL allows specification
of a list of IPv6 addresses that will be ignored
if they appear in a domain name's AAAA records, and
DNS64 will be applied to any A records the domain
name owns. If not defined, <span class="command"><strong>exclude</strong></span>
defaults to ::ffff:0.0.0.0/96.
</p>
<p>
A optional <span class="command"><strong>suffix</strong></span> can also
be defined to set the bits trailing the mapped
IPv4 address bits. By default these bits are
set to <strong class="userinput"><code>::</code></strong>. The bits
matching the prefix and mapped IPv4 address
must be zero.
</p>
<p>
If <span class="command"><strong>recursive-only</strong></span> is set to
<span class="command"><strong>yes</strong></span> the DNS64 synthesis will
only happen for recursive queries. The default
is <span class="command"><strong>no</strong></span>.
</p>
<p>
If <span class="command"><strong>break-dnssec</strong></span> is set to
<span class="command"><strong>yes</strong></span> the DNS64 synthesis will
happen even if the result, if validated, would
cause a DNSSEC validation failure. If this option
is set to <span class="command"><strong>no</strong></span> (the default), the DO
is set on the incoming query, and there are RRSIGs on
the applicable records, then synthesis will not happen.
</p>
<pre class="programlisting">
acl rfc1918 { 10/8; 192.168/16; 172.16/12; };
dns64 64:FF9B::/96 {
clients { any; };
mapped { !rfc1918; any; };
exclude { 64:FF9B::/96; ::ffff:0000:0000/96; };
suffix ::;
};
</pre>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-loadkeys-interval</strong></span></span></dt>
<dd>
<p>
When a zone is configured with <span class="command"><strong>auto-dnssec
maintain;</strong></span> its key repository must be checked
periodically to see if any new keys have been added
or any existing keys' timing metadata has been updated
(see <a class="xref" href="man.dnssec-keygen.html" title="dnssec-keygen"><span class="refentrytitle"><span class="application">dnssec-keygen</span></span>(8)</a> and
<a class="xref" href="man.dnssec-settime.html" title="dnssec-settime"><span class="refentrytitle"><span class="application">dnssec-settime</span></span>(8)</a>). The
<span class="command"><strong>dnssec-loadkeys-interval</strong></span> option
sets the frequency of automatic repository checks, in
minutes. The default is <code class="literal">60</code> (1 hour),
the minimum is <code class="literal">1</code> (1 minute), and the
maximum is <code class="literal">1440</code> (24 hours); any higher
value is silently reduced.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-update-mode</strong></span></span></dt>
<dd>
<p>
If this option is set to its default value of
<code class="literal">maintain</code> in a zone of type
<code class="literal">master</code> which is DNSSEC-signed
and configured to allow dynamic updates (see
<a class="xref" href="Bv9ARM.ch06.html#dynamic_update_policies" title="Dynamic Update Policies">the section called “Dynamic Update Policies”</a>), and
if <span class="command"><strong>named</strong></span> has access to the
private signing key(s) for the zone, then
<span class="command"><strong>named</strong></span> will automatically sign all new
or changed records and maintain signatures for the zone
by regenerating RRSIG records whenever they approach
their expiration date.
</p>
<p>
If the option is changed to <code class="literal">no-resign</code>,
then <span class="command"><strong>named</strong></span> will sign all new or
changed records, but scheduled maintenance of
signatures is disabled.
</p>
<p>
With either of these settings, <span class="command"><strong>named</strong></span>
will reject updates to a DNSSEC-signed zone when the
signing keys are inactive or unavailable to
<span class="command"><strong>named</strong></span>. (A planned third option,
<code class="literal">external</code>, will disable all automatic
signing and allow DNSSEC data to be submitted into a zone
via dynamic update; this is not yet implemented.)
</p>
</dd>
<dt><span class="term"><span class="command"><strong>nta-lifetime</strong></span></span></dt>
<dd>
<p>
Species the default lifetime, in seconds,
that will be used for negative trust anchors added
via <span class="command"><strong>rndc nta</strong></span>.
</p>
<p>
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), <span class="command"><strong>named</strong></span> will
abort the DNSSEC validation process and treat the data as
insecure rather than bogus. This continues until the
NTA's lifetime is elapsed. NTAs persist
across <span class="command"><strong>named</strong></span> restarts.
</p>
<p>
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.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>nta-recheck</strong></span></span></dt>
<dd>
<p>
Species how often to check whether negative
trust anchors added via <span class="command"><strong>rndc nta</strong></span>
are still necessary.
</p>
<p>
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,
<span class="command"><strong>named</strong></span> will periodically send a
query to the domain, ignoring negative trust anchors,
to find out whether it can now be validated. If so,
the negative trust anchor is allowed to expire early.
</p>
<p>
Validity checks can be disabled for an individual
NTA by using <span class="command"><strong>rndc nta -f</strong></span>, or
for all NTAs by setting <code class="option">nta-recheck</code>
to zero.
</p>
<p>
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).
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-zone-ttl</strong></span></span></dt>
<dd>
<p>
Specifies a maximum permissible TTL value in seconds.
For convenience, TTL-style time unit suffixes may be
used to specify the maximum value.
When loading a zone file using a
<code class="option">masterfile-format</code> of
<code class="constant">text</code> or <code class="constant">raw</code>,
any record encountered with a TTL higher than
<code class="option">max-zone-ttl</code> will cause the zone to
be rejected.
</p>
<p>
This is useful in DNSSEC-signed zones because when
rolling to a new DNSKEY, the old key needs to remain
available until RRSIG records have expired from
caches. The <code class="option">max-zone-ttl</code> option guarantees
that the largest TTL in the zone will be no higher
than the set value.
</p>
<p>
(NOTE: Because <code class="constant">map</code>-format files
load directly into memory, this option cannot be
used with them.)
</p>
<p>
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>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>serial-update-method</strong></span></span></dt>
<dd>
<p>
Zones configured for dynamic DNS may use this
option to set the update method that will be used for
the zone serial number in the SOA record.
</p>
<p>
With the default setting of
<span class="command"><strong>serial-update-method increment;</strong></span>, the
SOA serial number will be incremented by one each time
the zone is updated.
</p>
<p>
When set to
<span class="command"><strong>serial-update-method unixtime;</strong></span>, the
SOA serial number will be set to the number of seconds
since the UNIX epoch, unless the serial number is
already greater than or equal to that value, in which
case it is simply incremented by one.
</p>
<p>
When set to
<span class="command"><strong>serial-update-method date;</strong></span>, the
new SOA serial number will be the current date
in the form "YYYYMMDD", followed by two zeroes,
unless the existing serial number is already greater
than or equal to that value, in which case it is
incremented by one.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>zone-statistics</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>full</code></strong>, the server will collect
statistical data on all zones (unless specifically
turned off on a per-zone basis by specifying
<span class="command"><strong>zone-statistics terse</strong></span> or
<span class="command"><strong>zone-statistics none</strong></span>
in the <span class="command"><strong>zone</strong></span> statement).
The default is <strong class="userinput"><code>terse</code></strong>, providing
minimal statistics on zones (including name and
current serial number, but not query type
counters).
</p>
<p>
These statistics may be accessed via the
<span class="command"><strong>statistics-channel</strong></span> or
using <span class="command"><strong>rndc stats</strong></span>, which
will dump them to the file listed
in the <span class="command"><strong>statistics-file</strong></span>. See
also <a class="xref" href="Bv9ARM.ch06.html#statsfile" title="The Statistics File">the section called “The Statistics File”</a>.
</p>
<p>
For backward compatibility with earlier versions
of BIND 9, the <span class="command"><strong>zone-statistics</strong></span>
option can also accept <strong class="userinput"><code>yes</code></strong>
or <strong class="userinput"><code>no</code></strong>; <strong class="userinput"><code>yes</code></strong>
has the same meaning as <strong class="userinput"><code>full</code></strong>.
As of <acronym class="acronym">BIND</acronym> 9.10,
<strong class="userinput"><code>no</code></strong> has the same meaning
as <strong class="userinput"><code>none</code></strong>; previously, it
was the same as <strong class="userinput"><code>terse</code></strong>.
</p>
</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><span class="term"><span class="command"><strong>automatic-interface-scan</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>yes</code></strong> and supported by the OS,
automatically rescan network interfaces when the interface
addresses are added or removed. The default is
<strong class="userinput"><code>yes</code></strong>.
</p>
<p>
Currently the OS needs to support routing sockets for
<span class="command"><strong>automatic-interface-scan</strong></span> to be
supported.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-new-zones</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>yes</code></strong>, then zones can be
added at runtime via <span class="command"><strong>rndc addzone</strong></span>.
The default is <strong class="userinput"><code>no</code></strong>.
</p>
<p>
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"><em class="replaceable"><code>viewname</code></em>.nzf</code>
(or, if <span class="command"><strong>named</strong></span> is compiled with
liblmdb, in an LMDB database file called
<code class="filename"><em class="replaceable"><code>viewname</code></em>.nzd</code>).
<em class="replaceable"><code>viewname</code></em> 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.
</p>
<p>
Zones added at runtime will have their configuration
stored either in a new-zone file (NZF) or a new-zone
database (NZD) depending on whether
<span class="command"><strong>named</strong></span> was linked with
liblmdb at compile time.
See <a class="xref" href="man.rndc.html" title="rndc"><span class="refentrytitle"><span class="application">rndc</span></span>(8)</a> for further details
about <span class="command"><strong>rndc addzone</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>auth-nxdomain</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>yes</code></strong>, then the <span class="command"><strong>AA</strong></span> bit
is always set on NXDOMAIN responses, even if the server is
not actually
authoritative. The default is <strong class="userinput"><code>no</code></strong>;
this is
a change from <acronym class="acronym">BIND</acronym> 8. If you
are using very old DNS software, you
may need to set it to <strong class="userinput"><code>yes</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>deallocate-on-exit</strong></span></span></dt>
<dd>
<p>
This option was used in <acronym class="acronym">BIND</acronym>
8 to enable checking
for memory leaks on exit. <acronym class="acronym">BIND</acronym> 9 ignores the option and always performs
the checks.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>memstatistics</strong></span></span></dt>
<dd>
<p>
Write memory statistics to the file specified by
<span class="command"><strong>memstatistics-file</strong></span> at exit.
The default is <strong class="userinput"><code>no</code></strong> unless
'-m record' is specified on the command line in
which case it is <strong class="userinput"><code>yes</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dialup</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>yes</code></strong>, then the
server treats all zones as if they are doing zone transfers
across
a dial-on-demand dialup link, which can be brought up by
traffic
originating from this server. This has different effects
according
to zone type and concentrates the zone maintenance so that
it all
happens in a short interval, once every <span class="command"><strong>heartbeat-interval</strong></span> and
hopefully during the one call. It also suppresses some of
the normal
zone maintenance traffic. The default is <strong class="userinput"><code>no</code></strong>.
</p>
<p>
The <span class="command"><strong>dialup</strong></span> option
may also be specified in the <span class="command"><strong>view</strong></span> and
<span class="command"><strong>zone</strong></span> statements,
in which case it overrides the global <span class="command"><strong>dialup</strong></span>
option.
</p>
<p>
If the zone is a master zone, then the server will send out a
NOTIFY
request to all the slaves (default). This should trigger the
zone serial
number check in the slave (providing it supports NOTIFY)
allowing the slave
to verify the zone while the connection is active.
The set of servers to which NOTIFY is sent can be controlled
by
<span class="command"><strong>notify</strong></span> and <span class="command"><strong>also-notify</strong></span>.
</p>
<p>
If the
zone is a slave or stub zone, then the server will suppress
the regular
"zone up to date" (refresh) queries and only perform them
when the
<span class="command"><strong>heartbeat-interval</strong></span> expires in
addition to sending
NOTIFY requests.
</p>
<p>
Finer control can be achieved by using
<strong class="userinput"><code>notify</code></strong> which only sends NOTIFY
messages,
<strong class="userinput"><code>notify-passive</code></strong> which sends NOTIFY
messages and
suppresses the normal refresh queries, <strong class="userinput"><code>refresh</code></strong>
which suppresses normal refresh processing and sends refresh
queries
when the <span class="command"><strong>heartbeat-interval</strong></span>
expires, and
<strong class="userinput"><code>passive</code></strong> which just disables normal
refresh
processing.
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col 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>
<p>
dialup mode
</p>
</td>
<td>
<p>
normal refresh
</p>
</td>
<td>
<p>
heart-beat refresh
</p>
</td>
<td>
<p>
heart-beat notify
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>no</strong></span> (default)</p>
</td>
<td>
<p>
yes
</p>
</td>
<td>
<p>
no
</p>
</td>
<td>
<p>
no
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>yes</strong></span></p>
</td>
<td>
<p>
no
</p>
</td>
<td>
<p>
yes
</p>
</td>
<td>
<p>
yes
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>notify</strong></span></p>
</td>
<td>
<p>
yes
</p>
</td>
<td>
<p>
no
</p>
</td>
<td>
<p>
yes
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>refresh</strong></span></p>
</td>
<td>
<p>
no
</p>
</td>
<td>
<p>
yes
</p>
</td>
<td>
<p>
no
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>passive</strong></span></p>
</td>
<td>
<p>
no
</p>
</td>
<td>
<p>
no
</p>
</td>
<td>
<p>
no
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>notify-passive</strong></span></p>
</td>
<td>
<p>
no
</p>
</td>
<td>
<p>
no
</p>
</td>
<td>
<p>
yes
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Note that normal NOTIFY processing is not affected by
<span class="command"><strong>dialup</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>fake-iquery</strong></span></span></dt>
<dd>
<p>
In <acronym class="acronym">BIND</acronym> 8, this option
enabled simulating the obsolete DNS query type
IQUERY. <acronym class="acronym">BIND</acronym> 9 never does
IQUERY simulation.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>fetch-glue</strong></span></span></dt>
<dd>
<p>
This option is obsolete.
In BIND 8, <strong class="userinput"><code>fetch-glue yes</code></strong>
caused the server to attempt to fetch glue resource records
it
didn't have when constructing the additional
data section of a response. This is now considered a bad
idea
and BIND 9 never does it.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>flush-zones-on-shutdown</strong></span></span></dt>
<dd>
<p>
When the nameserver exits due receiving SIGTERM,
flush or do not flush any pending zone writes. The default
is
<span class="command"><strong>flush-zones-on-shutdown</strong></span> <strong class="userinput"><code>no</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>geoip-use-ecs</strong></span></span></dt>
<dd>
<p>
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
<span class="command"><strong>geoip-use-ecs</strong></span> <strong class="userinput"><code>yes</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>has-old-clients</strong></span></span></dt>
<dd>
<p>
This option was incorrectly implemented
in <acronym class="acronym">BIND</acronym> 8, and is ignored by <acronym class="acronym">BIND</acronym> 9.
To achieve the intended effect
of
<span class="command"><strong>has-old-clients</strong></span> <strong class="userinput"><code>yes</code></strong>, specify
the two separate options <span class="command"><strong>auth-nxdomain</strong></span> <strong class="userinput"><code>yes</code></strong>
and <span class="command"><strong>rfc2308-type1</strong></span> <strong class="userinput"><code>no</code></strong> instead.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>host-statistics</strong></span></span></dt>
<dd>
<p>
In BIND 8, this enabled keeping of
statistics for every host that the name server interacts
with.
Not implemented in BIND 9.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>root-key-sentinel</strong></span></span></dt>
<dd>
<p>
Respond to root key sentinel probes as described in
draft-ietf-dnsop-kskroll-sentinel-08. The default is
<strong class="userinput"><code>yes</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>maintain-ixfr-base</strong></span></span></dt>
<dd>
<p>
<span class="emphasis"><em>This option is obsolete</em></span>.
It was used in <acronym class="acronym">BIND</acronym> 8 to
determine whether a transaction log was
kept for Incremental Zone Transfer. <acronym class="acronym">BIND</acronym> 9 maintains a transaction
log whenever possible. If you need to disable outgoing
incremental zone
transfers, use <span class="command"><strong>provide-ixfr</strong></span> <strong class="userinput"><code>no</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>message-compression</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>yes</code></strong>, DNS name compression is
used in responses to regular queries (not including
AXFR or IXFR, which always uses compression). Setting
this option to <strong class="userinput"><code>no</code></strong> 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 <strong class="userinput"><code>yes</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>minimal-responses</strong></span></span></dt>
<dd>
<p>
If set to <strong class="userinput"><code>yes</code></strong>, then when generating
responses the server will only add records to the authority
and additional data sections when they are required (e.g.
delegations, negative responses). This may improve the
performance of the server.
</p>
<p>
When set to <strong class="userinput"><code>no-auth</code></strong>, the
server will omit records from the authority section
unless they are required, but it may still add
records to the additional section. When set to
<strong class="userinput"><code>no-auth-recursive</code></strong>, this
is only done if the query is recursive. These
settings are useful when answering stub clients,
which usually ignore the authority section.
<strong class="userinput"><code>no-auth-recursive</code></strong> is
designed for mixed-mode servers which handle
both authoritative and recursive queries.
</p>
<p>
The default is <strong class="userinput"><code>no</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>minimal-any</strong></span></span></dt>
<dd>
<p>
If set to <strong class="userinput"><code>yes</code></strong>, then when
generating a positive response to a query of type
ANY over UDP, the server will reply with only one
of the RRsets for the query name, and its covering
RRSIGs if any, instead of replying with all known
RRsets for the name. Similarly, a query for type
RRSIG will be answered with the RRSIG records covering
only one type. This can reduce the impact of some kinds
of attack traffic, without harming legitimate
clients. (Note, however, that the RRset returned is the
first one found in the database; it is not necessarily
the smallest available RRset.)
Additionally, <code class="option">minimal-responses</code> is
turned on for these queries, so no unnecessary records
will be added to the authority or additional sections.
The default is <strong class="userinput"><code>no</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>multiple-cnames</strong></span></span></dt>
<dd>
<p>
This option was used in <acronym class="acronym">BIND</acronym> 8 to allow
a domain name to have multiple CNAME records in violation of
the DNS standards. <acronym class="acronym">BIND</acronym> 9.2 onwards
always strictly enforces the CNAME rules both in master
files and dynamic updates.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>notify</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>yes</code></strong> (the default),
DNS NOTIFY messages are sent when a zone the server is
authoritative for
changes, see <a class="xref" href="Bv9ARM.ch04.html#notify" title="Notify">the section called “Notify”</a>. The messages are
sent to the
servers listed in the zone's NS records (except the master
server identified
in the SOA MNAME field), and to any servers listed in the
<span class="command"><strong>also-notify</strong></span> option.
</p>
<p>
If <strong class="userinput"><code>master-only</code></strong>, notifies are only
sent
for master zones.
If <strong class="userinput"><code>explicit</code></strong>, notifies are sent only
to
servers explicitly listed using <span class="command"><strong>also-notify</strong></span>.
If <strong class="userinput"><code>no</code></strong>, no notifies are sent.
</p>
<p>
The <span class="command"><strong>notify</strong></span> option may also be
specified in the <span class="command"><strong>zone</strong></span>
statement,
in which case it overrides the <span class="command"><strong>options notify</strong></span> statement.
It would only be necessary to turn off this option if it
caused slaves
to crash.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>notify-to-soa</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>yes</code></strong> do not check the nameservers
in the NS RRset against the SOA MNAME. Normally a NOTIFY
message is not sent to the SOA MNAME (SOA ORIGIN) as it is
supposed to contain the name of the ultimate master.
Sometimes, however, a slave is listed as the SOA MNAME in
hidden master configurations and in that case you would
want the ultimate master to still send NOTIFY messages to
all the nameservers listed in the NS RRset.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>recursion</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>yes</code></strong>, and a
DNS query requests recursion, then the server will attempt
to do
all the work required to answer the query. If recursion is
off
and the server does not already know the answer, it will
return a
referral response. The default is
<strong class="userinput"><code>yes</code></strong>.
Note that setting <span class="command"><strong>recursion no</strong></span> does not prevent
clients from getting data from the server's cache; it only
prevents new data from being cached as an effect of client
queries.
Caching may still occur as an effect the server's internal
operation, such as NOTIFY address lookups.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>request-nsid</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>yes</code></strong>, then an empty EDNS(0)
NSID (Name Server Identifier) option is sent with all
queries to authoritative name servers during iterative
resolution. If the authoritative server returns an NSID
option in its response, then its contents are logged in
the <span class="command"><strong>resolver</strong></span> category at level
<span class="command"><strong>info</strong></span>.
The default is <strong class="userinput"><code>no</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>request-sit</strong></span></span></dt>
<dd>
<p>
This experimental option is obsolete.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>require-server-cookie</strong></span></span></dt>
<dd>
<p>
Require a valid server cookie before sending a full
response to a UDP request from a cookie aware client.
BADCOOKIE is sent if there is a bad or no existent
server cookie.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>answer-cookie</strong></span></span></dt>
<dd>
<p>
When set to the default value of <strong class="userinput"><code>yes</code></strong>,
COOKIE EDNS options will be sent when applicable in
replies to client queries. If set to
<strong class="userinput"><code>no</code></strong>, COOKIE EDNS options will not
be sent in replies. This can only be set at the global
options level, not per-view.
</p>
<p>
<span class="command"><strong>answer-cookie no</strong></span> is only intended as a
temporary measure, for use when <span class="command"><strong>named</strong></span>
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.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>send-cookie</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>yes</code></strong>, then a COOKIE EDNS
option is sent along with the query. If the
resolver has previously talked to the server, the
COOKIE returned in the previous transaction is sent.
This is used by the server to determine whether
the resolver has talked to it before. A resolver
sending the correct COOKIE is assumed not to be an
off-path attacker sending a spoofed-source query;
the query is therefore unlikely to be part of a
reflection/amplification attack, so resolvers
sending a correct COOKIE option are not subject to
response rate limiting (RRL). Resolvers which
do not send a correct COOKIE option may be limited
to receiving smaller responses via the
<span class="command"><strong>nocookie-udp-size</strong></span> option.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>nocookie-udp-size</strong></span></span></dt>
<dd>
<p>
Sets the maximum size of UDP responses that will be
sent to queries without a valid server COOKIE. A value
below 128 will be silently raised to 128. The default
value is 4096, but the <span class="command"><strong>max-udp-size</strong></span>
option may further limit the response size.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>sit-secret</strong></span></span></dt>
<dd>
<p>
This experimental option is obsolete.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>cookie-algorithm</strong></span></span></dt>
<dd>
<p>
Set the algorithm to be used when generating the
server cookie. One of "aes", "sha1" or "sha256".
The default is "aes" if supported by the cryptographic
library or otherwise "sha256".
</p>
</dd>
<dt><span class="term"><span class="command"><strong>cookie-secret</strong></span></span></dt>
<dd>
<p>
If set, this is a shared secret used for generating
and verifying EDNS COOKIE options
within an anycast cluster. If not set, the system
will generate a random secret at startup. The
shared secret is encoded as a hex string and needs
to be 128 bits for AES128, 160 bits for SHA1 and
256 bits for SHA256.
</p>
<p>
If there are multiple secrets specified, the first
one listed in <code class="filename">named.conf</code> is
used to generate new server cookies. The others
will only be used to verify returned cookies.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>rfc2308-type1</strong></span></span></dt>
<dd>
<p>
Setting this to <strong class="userinput"><code>yes</code></strong> will
cause the server to send NS records along with the SOA
record for negative
answers. The default is <strong class="userinput"><code>no</code></strong>.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
Not yet implemented in <acronym class="acronym">BIND</acronym>
9.
</p>
</div>
</dd>
<dt><span class="term"><span class="command"><strong>trust-anchor-telemetry</strong></span></span></dt>
<dd>
<p>
Causes <span class="command"><strong>named</strong></span> to send specially-formed
queries once per day to domains for which trust anchors
have been configured via <span class="command"><strong>trusted-keys</strong></span>,
<span class="command"><strong>managed-keys</strong></span>, or
<span class="command"><strong>dnssec-validation auto</strong></span>.
</p>
<p>
The query name used for these queries has the
form "_ta-xxxx(-xxxx)(...)".<domain>, 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.
</p>
<p>
By monitoring these queries, zone operators will
be able to see which resolvers have been updated to
trust a new key; this may help them decide when it
is safe to remove an old one.
</p>
<p>
The default is <strong class="userinput"><code>yes</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>use-id-pool</strong></span></span></dt>
<dd>
<p>
<span class="emphasis"><em>This option is obsolete</em></span>.
<acronym class="acronym">BIND</acronym> 9 always allocates query
IDs from a pool.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>use-ixfr</strong></span></span></dt>
<dd>
<p>
<span class="emphasis"><em>This option is obsolete</em></span>.
If you need to disable IXFR to a particular server or
servers, see
the information on the <span class="command"><strong>provide-ixfr</strong></span> option
in <a class="xref" href="Bv9ARM.ch06.html#server_statement_definition_and_usage" title="server Statement Definition and Usage">the section called “<span class="command"><strong>server</strong></span> Statement Definition and
Usage”</a>.
See also
<a class="xref" href="Bv9ARM.ch04.html#incremental_zone_transfers" title="Incremental Zone Transfers (IXFR)">the section called “Incremental Zone Transfers (IXFR)”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>provide-ixfr</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>provide-ixfr</strong></span> in
<a class="xref" href="Bv9ARM.ch06.html#server_statement_definition_and_usage" title="server Statement Definition and Usage">the section called “<span class="command"><strong>server</strong></span> Statement Definition and
Usage”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>request-ixfr</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>request-ixfr</strong></span> in
<a class="xref" href="Bv9ARM.ch06.html#server_statement_definition_and_usage" title="server Statement Definition and Usage">the section called “<span class="command"><strong>server</strong></span> Statement Definition and
Usage”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>request-expire</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>request-expire</strong></span> in
<a class="xref" href="Bv9ARM.ch06.html#server_statement_definition_and_usage" title="server Statement Definition and Usage">the section called “<span class="command"><strong>server</strong></span> Statement Definition and
Usage”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>treat-cr-as-space</strong></span></span></dt>
<dd>
<p>
This option was used in <acronym class="acronym">BIND</acronym>
8 to make
the server treat carriage return ("<span class="command"><strong>\r</strong></span>") characters the same way
as a space or tab character,
to facilitate loading of zone files on a UNIX system that
were generated
on an NT or DOS machine. In <acronym class="acronym">BIND</acronym> 9, both UNIX "<span class="command"><strong>\n</strong></span>"
and NT/DOS "<span class="command"><strong>\r\n</strong></span>" newlines
are always accepted,
and the option is ignored.
</p>
</dd>
<dt>
<span class="term"><span class="command"><strong>additional-from-auth</strong></span>, </span><span class="term"><span class="command"><strong>additional-from-cache</strong></span></span>
</dt>
<dd>
<p>
These options control the behavior of an authoritative
server when
answering queries which have additional data, or when
following CNAME
and DNAME chains.
</p>
<p>
When both of these options are set to <strong class="userinput"><code>yes</code></strong>
(the default) and a
query is being answered from authoritative data (a zone
configured into the server), the additional data section of
the
reply will be filled in using data from other authoritative
zones
and from the cache. In some situations this is undesirable,
such
as when there is concern over the correctness of the cache,
or
in servers where slave zones may be added and modified by
untrusted third parties. Also, avoiding
the search for this additional data will speed up server
operations
at the possible expense of additional queries to resolve
what would
otherwise be provided in the additional section.
</p>
<p>
For example, if a query asks for an MX record for host <code class="literal">foo.example.com</code>,
and the record found is "<code class="literal">MX 10 mail.example.net</code>", normally the address
records (A and AAAA) for <code class="literal">mail.example.net</code> will be provided as well,
if known, even though they are not in the example.com zone.
Setting these options to <span class="command"><strong>no</strong></span>
disables this behavior and makes
the server only search for additional data in the zone it
answers from.
</p>
<p>
These options are intended for use in authoritative-only
servers, or in authoritative-only views. Attempts to set
them to <span class="command"><strong>no</strong></span> without also
specifying
<span class="command"><strong>recursion no</strong></span> will cause the
server to
ignore the options and log a warning message.
</p>
<p>
Specifying <span class="command"><strong>additional-from-cache no</strong></span> actually
disables the use of the cache not only for additional data
lookups
but also when looking up the answer. This is usually the
desired
behavior in an authoritative-only server where the
correctness of
the cached data is an issue.
</p>
<p>
When a name server is non-recursively queried for a name
that is not
below the apex of any served zone, it normally answers with
an
"upwards referral" to the root servers or the servers of
some other
known parent of the query name. Since the data in an
upwards referral
comes from the cache, the server will not be able to provide
upwards
referrals when <span class="command"><strong>additional-from-cache no</strong></span>
has been specified. Instead, it will respond to such
queries
with REFUSED. This should not cause any problems since
upwards referrals are not required for the resolution
process.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>match-mapped-addresses</strong></span></span></dt>
<dd>
<p>
If <strong class="userinput"><code>yes</code></strong>, then an
IPv4-mapped IPv6 address will match any address match
list entries that match the corresponding IPv4 address.
</p>
<p>
This option was introduced to work around a kernel quirk
in some operating systems that causes IPv4 TCP
connections, such as zone transfers, to be accepted on an
IPv6 socket using mapped addresses. This caused address
match lists designed for IPv4 to fail to match. However,
<span class="command"><strong>named</strong></span> now solves this problem
internally. The use of this option is discouraged.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>filter-aaaa-on-v4</strong></span></span></dt>
<dd>
<p>
This option is only available when
<acronym class="acronym">BIND</acronym> 9 is compiled with the
<strong class="userinput"><code>--enable-filter-aaaa</code></strong> option on the
"configure" command line. It is intended to help the
transition from IPv4 to IPv6 by not giving IPv6 addresses
to DNS clients unless they have connections to the IPv6
Internet. This is not recommended unless absolutely
necessary. The default is <strong class="userinput"><code>no</code></strong>.
The <span class="command"><strong>filter-aaaa-on-v4</strong></span> option
may also be specified in <span class="command"><strong>view</strong></span> statements
to override the global <span class="command"><strong>filter-aaaa-on-v4</strong></span>
option.
</p>
<p>
If <strong class="userinput"><code>yes</code></strong>,
the DNS client is at an IPv4 address, in <span class="command"><strong>filter-aaaa</strong></span>,
and if the response does not include DNSSEC signatures,
then all AAAA records are deleted from the response.
This filtering applies to all responses and not only
authoritative responses.
</p>
<p>
If <strong class="userinput"><code>break-dnssec</code></strong>,
then AAAA records are deleted even when DNSSEC is enabled.
As suggested by the name, this makes the response not verify,
because the DNSSEC protocol is designed detect deletions.
</p>
<p>
This mechanism can erroneously cause other servers to
not give AAAA records to their clients.
A recursing server with both IPv6 and IPv4 network connections
that queries an authoritative server using this mechanism
via IPv4 will be denied AAAA records even if its client is
using IPv6.
</p>
<p>
This mechanism is applied to authoritative as well as
non-authoritative records.
A client using IPv4 that is not allowed recursion can
erroneously be given AAAA records because the server is not
allowed to check for A records.
</p>
<p>
Some AAAA records are given to IPv4 clients in glue records.
IPv4 clients that are servers can then erroneously
answer requests for AAAA records received via IPv4.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>filter-aaaa-on-v6</strong></span></span></dt>
<dd>
<p>
Identical to <span class="command"><strong>filter-aaaa-on-v4</strong></span>,
except it filters AAAA responses to queries from IPv6
clients instead of IPv4 clients. To filter all
responses, set both options to <strong class="userinput"><code>yes</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>ixfr-from-differences</strong></span></span></dt>
<dd>
<p>
When <strong class="userinput"><code>yes</code></strong> and the server loads a new
version of a master zone from its zone file or receives a
new version of a slave file via zone transfer, it will
compare the new version to the previous one and calculate
a set of differences. The differences are then logged in
the zone's journal file such that the changes can be
transmitted to downstream slaves as an incremental zone
transfer.
</p>
<p>
By allowing incremental zone transfers to be used for
non-dynamic zones, this option saves bandwidth at the
expense of increased CPU and memory consumption at the
master.
In particular, if the new version of a zone is completely
different from the previous one, the set of differences
will be of a size comparable to the combined size of the
old and new zone version, and the server will need to
temporarily allocate memory to hold this complete
difference set.
</p>
<p><span class="command"><strong>ixfr-from-differences</strong></span>
also accepts <span class="command"><strong>master</strong></span> and
<span class="command"><strong>slave</strong></span> at the view and options
levels which causes
<span class="command"><strong>ixfr-from-differences</strong></span> to be enabled for
all <span class="command"><strong>master</strong></span> or
<span class="command"><strong>slave</strong></span> zones respectively.
It is off by default.
</p>
<p>
Note: if inline signing is enabled for a zone, the
user-provided <span class="command"><strong>ixfr-from-differences</strong></span>
setting is ignored for that zone.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>multi-master</strong></span></span></dt>
<dd>
<p>
This should be set when you have multiple masters for a zone
and the
addresses refer to different machines. If <strong class="userinput"><code>yes</code></strong>, <span class="command"><strong>named</strong></span> will
not log
when the serial number on the master is less than what <span class="command"><strong>named</strong></span>
currently
has. The default is <strong class="userinput"><code>no</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>auto-dnssec</strong></span></span></dt>
<dd>
<p>
Zones configured for dynamic DNS may use this
option to allow varying levels of automatic DNSSEC key
management. There are three possible settings:
</p>
<p>
<span class="command"><strong>auto-dnssec allow;</strong></span> permits
keys to be updated and the zone fully re-signed
whenever the user issues the command <span class="command"><strong>rndc sign
<em class="replaceable"><code>zonename</code></em></strong></span>.
</p>
<p>
<span class="command"><strong>auto-dnssec maintain;</strong></span> includes the
above, but also automatically adjusts the zone's DNSSEC
keys on schedule, according to the keys' timing metadata
(see <a class="xref" href="man.dnssec-keygen.html" title="dnssec-keygen"><span class="refentrytitle"><span class="application">dnssec-keygen</span></span>(8)</a> and
<a class="xref" href="man.dnssec-settime.html" title="dnssec-settime"><span class="refentrytitle"><span class="application">dnssec-settime</span></span>(8)</a>). The command
<span class="command"><strong>rndc sign
<em class="replaceable"><code>zonename</code></em></strong></span> causes
<span class="command"><strong>named</strong></span> to load keys from the key
repository and sign the zone with all keys that are
active.
<span class="command"><strong>rndc loadkeys
<em class="replaceable"><code>zonename</code></em></strong></span> causes
<span class="command"><strong>named</strong></span> to load keys from the key
repository and schedule key maintenance events to occur
in the future, but it does not sign the full zone
immediately. Note: once keys have been loaded for a
zone the first time, the repository will be searched
for changes periodically, regardless of whether
<span class="command"><strong>rndc loadkeys</strong></span> is used. The recheck
interval is defined by
<span class="command"><strong>dnssec-loadkeys-interval</strong></span>.)
</p>
<p>
The default setting is <span class="command"><strong>auto-dnssec off</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-enable</strong></span></span></dt>
<dd>
<p>
This indicates whether DNSSEC-related resource
records are to be returned by <span class="command"><strong>named</strong></span>.
If set to <strong class="userinput"><code>no</code></strong>,
<span class="command"><strong>named</strong></span> will not return DNSSEC-related
resource records unless specifically queried for.
The default is <strong class="userinput"><code>yes</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-validation</strong></span></span></dt>
<dd>
<p>
Enable DNSSEC validation in <span class="command"><strong>named</strong></span>.
Note <span class="command"><strong>dnssec-enable</strong></span> also needs to be
set to <strong class="userinput"><code>yes</code></strong> to be effective.
If set to <strong class="userinput"><code>no</code></strong>, DNSSEC validation
is disabled.
</p>
<p>
If set to <strong class="userinput"><code>auto</code></strong>, DNSSEC validation
is enabled, and a default trust anchor for the DNS root
zone is used. If set to <strong class="userinput"><code>yes</code></strong>,
DNSSEC validation is enabled, but a trust anchor must be
manually configured using a <span class="command"><strong>trusted-keys</strong></span>
or <span class="command"><strong>managed-keys</strong></span> statement. The default
is <strong class="userinput"><code>yes</code></strong>.
</p>
<p>
The default root trust anchor is stored in the file
<code class="filename">bind.keys</code>.
<span class="command"><strong>named</strong></span> will load that key at
startup if <span class="command"><strong>dnssec-validation</strong></span> 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>.
</p>
<p>
To prevent problems if <code class="filename">bind.keys</code> is
not found, the current trust anchor is also compiled in
to <span class="command"><strong>named</strong></span>. Relying on this is not
recommended, however, as it requires <span class="command"><strong>named</strong></span>
to be recompiled with a new key when the root key expires.)
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
<span class="command"><strong>named</strong></span> <span class="emphasis"><em>only</em></span>
loads the root key from <code class="filename">bind.keys</code>.
The file cannot be used to store keys for other zones.
The root key in <code class="filename">bind.keys</code> is ignored
if <span class="command"><strong>dnssec-validation auto</strong></span> is not in
use.
</p>
<p>
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
<span class="command"><strong>dnssec-validation</strong></span> is off.
</p>
</div>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-accept-expired</strong></span></span></dt>
<dd>
<p>
Accept expired signatures when verifying DNSSEC signatures.
The default is <strong class="userinput"><code>no</code></strong>.
Setting this option to <strong class="userinput"><code>yes</code></strong>
leaves <span class="command"><strong>named</strong></span> vulnerable to
replay attacks.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>querylog</strong></span></span></dt>
<dd>
<p>
Specify whether query logging should be started when <span class="command"><strong>named</strong></span>
starts.
If <span class="command"><strong>querylog</strong></span> is not specified,
then the query logging
is determined by the presence of the logging category <span class="command"><strong>queries</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-names</strong></span></span></dt>
<dd>
<p>
This option is used to restrict the character set and syntax
of
certain domain names in master files and/or DNS responses
received
from the network. The default varies according to usage
area. For
<span class="command"><strong>master</strong></span> zones the default is <span class="command"><strong>fail</strong></span>.
For <span class="command"><strong>slave</strong></span> zones the default
is <span class="command"><strong>warn</strong></span>.
For answers received from the network (<span class="command"><strong>response</strong></span>)
the default is <span class="command"><strong>ignore</strong></span>.
</p>
<p>
The rules for legal hostnames and mail domains are derived
from RFC 952 and RFC 821 as modified by RFC 1123.
</p>
<p><span class="command"><strong>check-names</strong></span>
applies to the owner names of A, AAAA and MX records.
It also applies to the domain names in the RDATA of NS, SOA,
MX, and SRV records.
It also applies to the RDATA of PTR records where the owner
name indicated that it is a reverse lookup of a hostname
(the owner name ends in IN-ADDR.ARPA, IP6.ARPA, or IP6.INT).
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-dup-records</strong></span></span></dt>
<dd>
<p>
Check master zones for records that are treated as different
by DNSSEC but are semantically equal in plain DNS. The
default is to <span class="command"><strong>warn</strong></span>. Other possible
values are <span class="command"><strong>fail</strong></span> and
<span class="command"><strong>ignore</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-mx</strong></span></span></dt>
<dd>
<p>
Check whether the MX record appears to refer to a IP address.
The default is to <span class="command"><strong>warn</strong></span>. Other possible
values are <span class="command"><strong>fail</strong></span> and
<span class="command"><strong>ignore</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-wildcard</strong></span></span></dt>
<dd>
<p>
This option is used to check for non-terminal wildcards.
The use of non-terminal wildcards is almost always as a
result of a failure
to understand the wildcard matching algorithm (RFC 1034).
This option
affects master zones. The default (<span class="command"><strong>yes</strong></span>) is to check
for non-terminal wildcards and issue a warning.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-integrity</strong></span></span></dt>
<dd>
<p>
Perform post load zone integrity checks on master
zones. This checks that MX and SRV records refer
to address (A or AAAA) records and that glue
address records exist for delegated zones. For
MX and SRV records only in-zone hostnames are
checked (for out-of-zone hostnames use
<span class="command"><strong>named-checkzone</strong></span>).
For NS records only names below top of zone are
checked (for out-of-zone names and glue consistency
checks use <span class="command"><strong>named-checkzone</strong></span>).
The default is <span class="command"><strong>yes</strong></span>.
</p>
<p>
The use of the SPF record for publishing Sender
Policy Framework is deprecated as the migration
from using TXT records to SPF records was abandoned.
Enabling this option also checks that a TXT Sender
Policy Framework record exists (starts with "v=spf1")
if there is an SPF record. Warnings are emitted if the
TXT record does not exist and can be suppressed with
<span class="command"><strong>check-spf</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-mx-cname</strong></span></span></dt>
<dd>
<p>
If <span class="command"><strong>check-integrity</strong></span> is set then
fail, warn or ignore MX records that refer
to CNAMES. The default is to <span class="command"><strong>warn</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-srv-cname</strong></span></span></dt>
<dd>
<p>
If <span class="command"><strong>check-integrity</strong></span> is set then
fail, warn or ignore SRV records that refer
to CNAMES. The default is to <span class="command"><strong>warn</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-sibling</strong></span></span></dt>
<dd>
<p>
When performing integrity checks, also check that
sibling glue exists. The default is <span class="command"><strong>yes</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-spf</strong></span></span></dt>
<dd>
<p>
If <span class="command"><strong>check-integrity</strong></span> is set then
check that there is a TXT Sender Policy Framework
record present (starts with "v=spf1") if there is an
SPF record present. The default is
<span class="command"><strong>warn</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>zero-no-soa-ttl</strong></span></span></dt>
<dd>
<p>
When returning authoritative negative responses to
SOA queries set the TTL of the SOA record returned in
the authority section to zero.
The default is <span class="command"><strong>yes</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>zero-no-soa-ttl-cache</strong></span></span></dt>
<dd>
<p>
When caching a negative response to a SOA query
set the TTL to zero.
The default is <span class="command"><strong>no</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>update-check-ksk</strong></span></span></dt>
<dd>
<p>
When set to the default value of <code class="literal">yes</code>,
check the KSK bit in each key to determine how the key
should be used when generating RRSIGs for a secure zone.
</p>
<p>
Ordinarily, zone-signing keys (that is, keys without the
KSK bit set) are used to sign the entire zone, while
key-signing keys (keys with the KSK bit set) are only
used to sign the DNSKEY RRset at the zone apex.
However, if this option is set to <code class="literal">no</code>,
then the KSK bit is ignored; KSKs are treated as if they
were ZSKs and are used to sign the entire zone. This is
similar to the <span class="command"><strong>dnssec-signzone -z</strong></span>
command line option.
</p>
<p>
When this option is set to <code class="literal">yes</code>, there
must be at least two active keys for every algorithm
represented in the DNSKEY RRset: at least one KSK and one
ZSK per algorithm. If there is any algorithm for which
this requirement is not met, this option will be ignored
for that algorithm.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-dnskey-kskonly</strong></span></span></dt>
<dd>
<p>
When this option and <span class="command"><strong>update-check-ksk</strong></span>
are both set to <code class="literal">yes</code>, only key-signing
keys (that is, keys with the KSK bit set) will be used
to sign the DNSKEY RRset at the zone apex. Zone-signing
keys (keys without the KSK bit set) will be used to sign
the remainder of the zone, but not the DNSKEY RRset.
This is similar to the
<span class="command"><strong>dnssec-signzone -x</strong></span> command line option.
</p>
<p>
The default is <span class="command"><strong>no</strong></span>. If
<span class="command"><strong>update-check-ksk</strong></span> is set to
<code class="literal">no</code>, this option is ignored.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>try-tcp-refresh</strong></span></span></dt>
<dd>
<p>
Try to refresh the zone using TCP if UDP queries fail.
For BIND 8 compatibility, the default is
<span class="command"><strong>yes</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-secure-to-insecure</strong></span></span></dt>
<dd>
<p>
Allow a dynamic zone to transition from secure to
insecure (i.e., signed to unsigned) by deleting all
of the DNSKEY records. The default is <span class="command"><strong>no</strong></span>.
If set to <span class="command"><strong>yes</strong></span>, and if the DNSKEY RRset
at the zone apex is deleted, all RRSIG and NSEC records
will be removed from the zone as well.
</p>
<p>
If the zone uses NSEC3, then it is also necessary to
delete the NSEC3PARAM RRset from the zone apex; this will
cause the removal of all corresponding NSEC3 records.
(It is expected that this requirement will be eliminated
in a future release.)
</p>
<p>
Note that if a zone has been configured with
<span class="command"><strong>auto-dnssec maintain</strong></span> and the
private keys remain accessible in the key repository,
then the zone will be automatically signed again the
next time <span class="command"><strong>named</strong></span> is started.
</p>
</dd>
</dl></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="forwarding"></a>Forwarding</h4></div></div></div>
<p>
The forwarding facility can be used to create a large site-wide
cache on a few servers, reducing traffic over links to external
name servers. It can also be used to allow queries by servers that
do not have direct access to the Internet, but wish to look up
exterior
names anyway. Forwarding occurs only on those queries for which
the server is not authoritative and does not have the answer in
its cache.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>forward</strong></span></span></dt>
<dd>
<p>
This option is only meaningful if the
forwarders list is not empty. A value of <code class="varname">first</code>,
the default, causes the server to query the forwarders
first — and
if that doesn't answer the question, the server will then
look for
the answer itself. If <code class="varname">only</code> is
specified, the
server will only query the forwarders.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>forwarders</strong></span></span></dt>
<dd>
<p>
Specifies the IP addresses to be used
for forwarding. The default is the empty list (no
forwarding).
</p>
</dd>
</dl></div>
<p>
Forwarding can also be configured on a per-domain basis, allowing
for the global forwarding options to be overridden in a variety
of ways. You can set particular domains to use different
forwarders,
or have a different <span class="command"><strong>forward only/first</strong></span> behavior,
or not forward at all, see <a class="xref" href="Bv9ARM.ch06.html#zone_statement_grammar" title="zone Statement Grammar">the section called “<span class="command"><strong>zone</strong></span>
Statement Grammar”</a>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="dual_stack"></a>Dual-stack Servers</h4></div></div></div>
<p>
Dual-stack servers are used as servers of last resort to work
around
problems in reachability due the lack of support for either IPv4
or IPv6
on the host machine.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>dual-stack-servers</strong></span></span></dt>
<dd>
<p>
Specifies host names or addresses of machines with access to
both IPv4 and IPv6 transports. If a hostname is used, the
server must be able
to resolve the name using only the transport it has. If the
machine is dual
stacked, then the <span class="command"><strong>dual-stack-servers</strong></span> have no effect unless
access to a transport has been disabled on the command line
(e.g. <span class="command"><strong>named -4</strong></span>).
</p>
</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>
<p>
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 “Address Match Lists”</a> for
details on how to specify IP address lists.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>allow-notify</strong></span></span></dt>
<dd>
<p>
Specifies which hosts are allowed to
notify this server, a slave, of zone changes in addition
to the zone masters.
<span class="command"><strong>allow-notify</strong></span> may also be
specified in the
<span class="command"><strong>zone</strong></span> statement, in which case
it overrides the
<span class="command"><strong>options allow-notify</strong></span>
statement. It is only meaningful
for a slave zone. If not specified, the default is to
process notify messages
only from a zone's master.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-query</strong></span></span></dt>
<dd>
<p>
Specifies which hosts are allowed to ask ordinary
DNS questions. <span class="command"><strong>allow-query</strong></span> may
also be specified in the <span class="command"><strong>zone</strong></span>
statement, in which case it overrides the
<span class="command"><strong>options allow-query</strong></span> statement.
If not specified, the default is to allow queries
from all hosts.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
<span class="command"><strong>allow-query-cache</strong></span> is now
used to specify access to the cache.
</p>
</div>
</dd>
<dt><span class="term"><span class="command"><strong>allow-query-on</strong></span></span></dt>
<dd>
<p>
Specifies which local addresses can accept ordinary
DNS questions. This makes it possible, for instance,
to allow queries on internal-facing interfaces but
disallow them on external-facing ones, without
necessarily knowing the internal network's addresses.
</p>
<p>
Note that <span class="command"><strong>allow-query-on</strong></span> is only
checked for queries that are permitted by
<span class="command"><strong>allow-query</strong></span>. A query must be
allowed by both ACLs, or it will be refused.
</p>
<p>
<span class="command"><strong>allow-query-on</strong></span> may
also be specified in the <span class="command"><strong>zone</strong></span>
statement, in which case it overrides the
<span class="command"><strong>options allow-query-on</strong></span> statement.
</p>
<p>
If not specified, the default is to allow queries
on all addresses.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
<span class="command"><strong>allow-query-cache</strong></span> is
used to specify access to the cache.
</p>
</div>
</dd>
<dt><span class="term"><span class="command"><strong>allow-query-cache</strong></span></span></dt>
<dd>
<p>
Specifies which hosts are allowed to get answers
from the cache. If <span class="command"><strong>allow-query-cache</strong></span>
is not set then <span class="command"><strong>allow-recursion</strong></span>
is used if set, otherwise <span class="command"><strong>allow-query</strong></span>
is used if set unless <span class="command"><strong>recursion no;</strong></span> is
set in which case <span class="command"><strong>none;</strong></span> is used,
otherwise the default (<span class="command"><strong>localnets;</strong></span>
<span class="command"><strong>localhost;</strong></span>) is used.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-query-cache-on</strong></span></span></dt>
<dd>
<p>
Specifies which local addresses can give answers
from the cache. If not specified, the default is
to allow cache queries on any address,
<span class="command"><strong>localnets</strong></span> and
<span class="command"><strong>localhost</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-recursion</strong></span></span></dt>
<dd>
<p>
Specifies which hosts are allowed to make recursive
queries through this server. If
<span class="command"><strong>allow-recursion</strong></span> is not set
then <span class="command"><strong>allow-query-cache</strong></span> is
used if set, otherwise <span class="command"><strong>allow-query</strong></span>
is used if set, otherwise the default
(<span class="command"><strong>localnets;</strong></span>
<span class="command"><strong>localhost;</strong></span>) is used.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-recursion-on</strong></span></span></dt>
<dd>
<p>
Specifies which local addresses can accept recursive
queries. If not specified, the default is to allow
recursive queries on all addresses.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-update</strong></span></span></dt>
<dd>
<p>
Specifies which hosts are allowed to
submit Dynamic DNS updates for master zones. The default is
to deny
updates from all hosts. Note that allowing updates based
on the requestor's IP address is insecure; see
<a class="xref" href="Bv9ARM.ch07.html#dynamic_update_security" title="Dynamic Update Security">the section called “Dynamic Update Security”</a> for details.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-update-forwarding</strong></span></span></dt>
<dd>
<p>
Specifies which hosts are allowed to
submit Dynamic DNS updates to slave zones to be forwarded to
the
master. The default is <strong class="userinput"><code>{ none; }</code></strong>,
which
means that no update forwarding will be performed. To
enable
update forwarding, specify
<strong class="userinput"><code>allow-update-forwarding { any; };</code></strong>.
Specifying values other than <strong class="userinput"><code>{ none; }</code></strong> or
<strong class="userinput"><code>{ any; }</code></strong> is usually
counterproductive, since
the responsibility for update access control should rest
with the
master server, not the slaves.
</p>
<p>
Note that enabling the update forwarding feature on a slave
server
may expose master servers relying on insecure IP address
based
access control to attacks; see <a class="xref" href="Bv9ARM.ch07.html#dynamic_update_security" title="Dynamic Update Security">the section called “Dynamic Update Security”</a>
for more details.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-v6-synthesis</strong></span></span></dt>
<dd>
<p>
This option was introduced for the smooth transition from
AAAA
to A6 and from "nibble labels" to binary labels.
However, since both A6 and binary labels were then
deprecated,
this option was also deprecated.
It is now ignored with some warning messages.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-transfer</strong></span></span></dt>
<dd>
<p>
Specifies which hosts are allowed to
receive zone transfers from the server. <span class="command"><strong>allow-transfer</strong></span> may
also be specified in the <span class="command"><strong>zone</strong></span>
statement, in which
case it overrides the <span class="command"><strong>options allow-transfer</strong></span> statement.
If not specified, the default is to allow transfers to all
hosts.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>blackhole</strong></span></span></dt>
<dd>
<p>
Specifies a list of addresses that the
server will not accept queries from or use to resolve a
query. Queries
from these addresses will not be responded to. The default
is <strong class="userinput"><code>none</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>filter-aaaa</strong></span></span></dt>
<dd>
<p>
Specifies a list of addresses to which
<span class="command"><strong>filter-aaaa-on-v4</strong></span>
and <span class="command"><strong>filter-aaaa-on-v6</strong></span>
apply. The default is <strong class="userinput"><code>any</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>keep-response-order</strong></span></span></dt>
<dd>
<p>
Specifies a list of addresses to which the server
will send responses to TCP queries in the same order
in which they were received. This disables the
processing of TCP queries in parallel. The default
is <strong class="userinput"><code>none</code></strong>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>no-case-compress</strong></span></span></dt>
<dd>
<p>
Specifies a list of addresses which require responses
to use case-insensitive compression. This ACL can be
used when <span class="command"><strong>named</strong></span> needs to work with
clients that do not comply with the requirement in RFC
1034 to use case-insensitive name comparisons when
checking for matching domain names.
</p>
<p>
If left undefined, the ACL defaults to
<span class="command"><strong>none</strong></span>: case-insensitive compression
will be used for all clients. If the ACL is defined and
matches a client, then case will be ignored when
compressing domain names in DNS responses sent to that
client.
</p>
<p>
This can result in slightly smaller responses: if
a response contains the names "example.com" and
"example.COM", case-insensitive compression would treat
the second one as a duplicate. It also ensures
that the case of the query name exactly matches the
case of the owner names of returned records, rather
than matching the case of the records entered in
the zone file. This allows responses to exactly
match the query, which is required by some clients
due to incorrect use of case-sensitive comparisons.
</p>
<p>
Case-insensitive compression is <span class="emphasis"><em>always</em></span>
used in AXFR and IXFR responses, regardless of whether
the client matches this ACL.
</p>
<p>
There are circumstances in which <span class="command"><strong>named</strong></span>
will not preserve the case of owner names of records:
if a zone file defines records of different types with
the same name, but the capitalization of the name is
different (e.g., "www.example.com/A" and
"WWW.EXAMPLE.COM/AAAA"), then all responses for that
name will use the <span class="emphasis"><em>first</em></span> version
of the name that was used in the zone file. This
limitation may be addressed in a future release. However,
domain names specified in the rdata of resource records
(i.e., records of type NS, MX, CNAME, etc) will always
have their case preserved unless the client matches this
ACL.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>resolver-query-timeout</strong></span></span></dt>
<dd>
<p>
The amount of time in seconds that the resolver
will spend attempting to resolve a recursive
query before failing. The default and minimum
is <code class="literal">10</code> and the maximum is
<code class="literal">30</code>. Setting it to
<code class="literal">0</code> will result in the default
being used.
</p>
</dd>
</dl></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="interfaces"></a>Interfaces</h4></div></div></div>
<p>
The interfaces and ports that the server will answer queries
from may be specified using the <span class="command"><strong>listen-on</strong></span> option. <span class="command"><strong>listen-on</strong></span> takes
an optional port and an <code class="varname">address_match_list</code>
of IPv4 addresses. (IPv6 addresses are ignored, with a
logged warning.)
The server will listen on all interfaces allowed by the address
match list. If a port is not specified, port 53 will be used.
</p>
<p>
Multiple <span class="command"><strong>listen-on</strong></span> statements are
allowed.
For example,
</p>
<pre class="programlisting">listen-on { 5.6.7.8; };
listen-on port 1234 { !1.2.3.4; 1.2/16; };
</pre>
<p>
will enable the name server on port 53 for the IP address
5.6.7.8, and on port 1234 of an address on the machine in net
1.2 that is not 1.2.3.4.
</p>
<p>
If no <span class="command"><strong>listen-on</strong></span> is specified, the
server will listen on port 53 on all IPv4 interfaces.
</p>
<p>
The <span class="command"><strong>listen-on-v6</strong></span> option is used to
specify the interfaces and the ports on which the server will
listen for incoming queries sent using IPv6. If not specified,
the server will listen on port 53 on all IPv6 interfaces.
</p>
<p>
When </p>
<pre class="programlisting">{ any; }</pre>
<p> is
specified
as the <code class="varname">address_match_list</code> for the
<span class="command"><strong>listen-on-v6</strong></span> option,
the server does not bind a separate socket to each IPv6 interface
address as it does for IPv4 if the operating system has enough API
support for IPv6 (specifically if it conforms to RFC 3493 and RFC
3542).
Instead, it listens on the IPv6 wildcard address.
If the system only has incomplete API support for IPv6, however,
the behavior is the same as that for IPv4.
</p>
<p>
A list of particular IPv6 addresses can also be specified, in
which case
the server listens on a separate socket for each specified
address,
regardless of whether the desired API is supported by the system.
IPv4 addresses specified in <span class="command"><strong>listen-on-v6</strong></span>
will be ignored, with a logged warning.
</p>
<p>
Multiple <span class="command"><strong>listen-on-v6</strong></span> options can
be used.
For example,
</p>
<pre class="programlisting">listen-on-v6 { any; };
listen-on-v6 port 1234 { !2001:db8::/32; any; };
</pre>
<p>
will enable the name server on port 53 for any IPv6 addresses
(with a single wildcard socket),
and on port 1234 of IPv6 addresses that is not in the prefix
2001:db8::/32 (with separate sockets for each matched address.)
</p>
<p>
To make the server not listen on any IPv6 address, use
</p>
<pre class="programlisting">listen-on-v6 { none; };
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="query_address"></a>Query Address</h4></div></div></div>
<p>
If the server doesn't know the answer to a question, it will
query other name servers. <span class="command"><strong>query-source</strong></span> specifies
the address and port used for such queries. For queries sent over
IPv6, there is a separate <span class="command"><strong>query-source-v6</strong></span> option.
If <span class="command"><strong>address</strong></span> is <span class="command"><strong>*</strong></span> (asterisk) or is omitted,
a wildcard IP address (<span class="command"><strong>INADDR_ANY</strong></span>)
will be used.
</p>
<p>
If <span class="command"><strong>port</strong></span> is <span class="command"><strong>*</strong></span> or is omitted,
a random port number from a pre-configured
range is picked up and will be used for each query.
The port range(s) is that specified in
the <span class="command"><strong>use-v4-udp-ports</strong></span> (for IPv4)
and <span class="command"><strong>use-v6-udp-ports</strong></span> (for IPv6)
options, excluding the ranges specified in
the <span class="command"><strong>avoid-v4-udp-ports</strong></span>
and <span class="command"><strong>avoid-v6-udp-ports</strong></span> options, respectively.
</p>
<p>
The defaults of the <span class="command"><strong>query-source</strong></span> and
<span class="command"><strong>query-source-v6</strong></span> options
are:
</p>
<pre class="programlisting">query-source address * port *;
query-source-v6 address * port *;
</pre>
<p>
If <span class="command"><strong>use-v4-udp-ports</strong></span> or
<span class="command"><strong>use-v6-udp-ports</strong></span> is unspecified,
<span class="command"><strong>named</strong></span> will check if the operating
system provides a programming interface to retrieve the
system's default range for ephemeral ports.
If such an interface is available,
<span class="command"><strong>named</strong></span> will use the corresponding system
default range; otherwise, it will use its own defaults:
</p>
<pre class="programlisting">use-v4-udp-ports { range 1024 65535; };
use-v6-udp-ports { range 1024 65535; };
</pre>
<p>
Note: make sure the ranges be sufficiently large for
security. A desirable size depends on various parameters,
but we generally recommend it contain at least 16384 ports
(14 bits of entropy).
Note also that the system's default range when used may be
too small for this purpose, and that the range may even be
changed while <span class="command"><strong>named</strong></span> is running; the new
range will automatically be applied when <span class="command"><strong>named</strong></span>
is reloaded.
It is encouraged to
configure <span class="command"><strong>use-v4-udp-ports</strong></span> and
<span class="command"><strong>use-v6-udp-ports</strong></span> explicitly so that the
ranges are sufficiently large and are reasonably
independent from the ranges used by other applications.
</p>
<p>
Note: the operational configuration
where <span class="command"><strong>named</strong></span> runs may prohibit the use
of some ports. For example, UNIX systems will not allow
<span class="command"><strong>named</strong></span> running without a root privilege
to use ports less than 1024.
If such ports are included in the specified (or detected)
set of query ports, the corresponding query attempts will
fail, resulting in resolution failures or delay.
It is therefore important to configure the set of ports
that can be safely used in the expected operational environment.
</p>
<p>
The defaults of the <span class="command"><strong>avoid-v4-udp-ports</strong></span> and
<span class="command"><strong>avoid-v6-udp-ports</strong></span> options
are:
</p>
<pre class="programlisting">avoid-v4-udp-ports {};
avoid-v6-udp-ports {};
</pre>
<p>
Note: BIND 9.5.0 introduced
the <span class="command"><strong>use-queryport-pool</strong></span>
option to support a pool of such random ports, but this
option is now obsolete because reusing the same ports in
the pool may not be sufficiently secure.
For the same reason, it is generally strongly discouraged to
specify a particular port for the
<span class="command"><strong>query-source</strong></span> or
<span class="command"><strong>query-source-v6</strong></span> options;
it implicitly disables the use of randomized port numbers.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>use-queryport-pool</strong></span></span></dt>
<dd>
<p>
This option is obsolete.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>queryport-pool-ports</strong></span></span></dt>
<dd>
<p>
This option is obsolete.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>queryport-pool-updateinterval</strong></span></span></dt>
<dd>
<p>
This option is obsolete.
</p>
</dd>
</dl></div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
The address specified in the <span class="command"><strong>query-source</strong></span> option
is used for both UDP and TCP queries, but the port applies only
to UDP queries. TCP queries always use a random
unprivileged port.
</p>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
Solaris 2.5.1 and earlier does not support setting the source
address for TCP sockets.
</p>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
See also <span class="command"><strong>transfer-source</strong></span> and
<span class="command"><strong>notify-source</strong></span>.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="zone_transfers"></a>Zone Transfers</h4></div></div></div>
<p>
<acronym class="acronym">BIND</acronym> has mechanisms in place to
facilitate zone transfers
and set limits on the amount of load that transfers place on the
system. The following options apply to zone transfers.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>also-notify</strong></span></span></dt>
<dd>
<p>
Defines a global list of IP addresses of name servers
that are also sent NOTIFY messages whenever a fresh copy of
the
zone is loaded, in addition to the servers listed in the
zone's NS records.
This helps to ensure that copies of the zones will
quickly converge on stealth servers.
Optionally, a port may be specified with each
<span class="command"><strong>also-notify</strong></span> address to send
the notify messages to a port other than the
default of 53.
An optional TSIG key can also be specified with each
address to cause the notify messages to be signed; this
can be useful when sending notifies to multiple views.
In place of explicit addresses, one or more named
<span class="command"><strong>masters</strong></span> lists can be used.
</p>
<p>
If an <span class="command"><strong>also-notify</strong></span> list
is given in a <span class="command"><strong>zone</strong></span> statement,
it will override
the <span class="command"><strong>options also-notify</strong></span>
statement. When a <span class="command"><strong>zone notify</strong></span>
statement
is set to <span class="command"><strong>no</strong></span>, the IP
addresses in the global <span class="command"><strong>also-notify</strong></span> list will
not be sent NOTIFY messages for that zone. The default is
the empty
list (no global notification list).
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-transfer-time-in</strong></span></span></dt>
<dd>
<p>
Inbound zone transfers running longer than
this many minutes will be terminated. The default is 120
minutes
(2 hours). The maximum value is 28 days (40320 minutes).
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-transfer-idle-in</strong></span></span></dt>
<dd>
<p>
Inbound zone transfers making no progress
in this many minutes will be terminated. The default is 60
minutes
(1 hour). The maximum value is 28 days (40320 minutes).
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-transfer-time-out</strong></span></span></dt>
<dd>
<p>
Outbound zone transfers running longer than
this many minutes will be terminated. The default is 120
minutes
(2 hours). The maximum value is 28 days (40320 minutes).
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-transfer-idle-out</strong></span></span></dt>
<dd>
<p>
Outbound zone transfers making no progress
in this many minutes will be terminated. The default is 60
minutes (1
hour). The maximum value is 28 days (40320 minutes).
</p>
</dd>
<dt><span class="term"><span class="command"><strong>notify-rate</strong></span></span></dt>
<dd>
<p>
The rate at which NOTIFY requests will be sent
during normal zone maintenance operations. (NOTIFY
requests due to initial zone loading are subject
to a separate rate limit; see below.) The default is
20 per second.
The lowest possible rate is one per second; when set
to zero, it will be silently raised to one.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>startup-notify-rate</strong></span></span></dt>
<dd>
<p>
The rate at which NOTIFY requests will be sent
when the name server is first starting up, or when
zones have been newly added to the nameserver.
The default is 20 per second.
The lowest possible rate is one per second; when set
to zero, it will be silently raised to one.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>serial-query-rate</strong></span></span></dt>
<dd>
<p>
Slave servers will periodically query master
servers to find out if zone serial numbers have
changed. Each such query uses a minute amount of
the slave server's network bandwidth. To limit
the amount of bandwidth used, BIND 9 limits the
rate at which queries are sent. The value of the
<span class="command"><strong>serial-query-rate</strong></span> option, an
integer, is the maximum number of queries sent
per second. The default is 20 per second.
The lowest possible rate is one per second; when set
to zero, it will be silently raised to one.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>serial-queries</strong></span></span></dt>
<dd>
<p>
In BIND 8, the <span class="command"><strong>serial-queries</strong></span>
option
set the maximum number of concurrent serial number queries
allowed to be outstanding at any given time.
BIND 9 does not limit the number of outstanding
serial queries and ignores the <span class="command"><strong>serial-queries</strong></span> option.
Instead, it limits the rate at which the queries are sent
as defined using the <span class="command"><strong>serial-query-rate</strong></span> option.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>transfer-format</strong></span></span></dt>
<dd>
<p>
Zone transfers can be sent using two different formats,
<span class="command"><strong>one-answer</strong></span> and
<span class="command"><strong>many-answers</strong></span>.
The <span class="command"><strong>transfer-format</strong></span> option is used
on the master server to determine which format it sends.
<span class="command"><strong>one-answer</strong></span> uses one DNS message per
resource record transferred.
<span class="command"><strong>many-answers</strong></span> packs as many resource
records as possible into a message.
<span class="command"><strong>many-answers</strong></span> is more efficient, but is
only supported by relatively new slave servers,
such as <acronym class="acronym">BIND</acronym> 9, <acronym class="acronym">BIND</acronym>
8.x and <acronym class="acronym">BIND</acronym> 4.9.5 onwards.
The <span class="command"><strong>many-answers</strong></span> format is also supported by
recent Microsoft Windows nameservers.
The default is <span class="command"><strong>many-answers</strong></span>.
<span class="command"><strong>transfer-format</strong></span> may be overridden on a
per-server basis by using the <span class="command"><strong>server</strong></span>
statement.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>transfer-message-size</strong></span></span></dt>
<dd>
<p>
This is an upper bound on the uncompressed size of DNS
messages used in zone transfers over TCP. If a message
grows larger than this size, additional messages will be
used to complete the zone transfer. (Note, however,
that this is a hint, not a hard limit; if a message
contains a single resource record whose RDATA does not
fit within the size limit, a larger message will be
permitted so the record can be transferred.)
</p>
<p>
Valid values are between 512 and 65535 octets, and any
values outside that range will be adjusted to the nearest
value within it. The default is <code class="literal">20480</code>,
which was selected to improve message compression:
most DNS messages of this size will compress to less
than 16536 bytes. Larger messages cannot be compressed
as effectively, because 16536 is the largest permissible
compression offset pointer in a DNS message.
</p>
<p>
This option is mainly intended for server testing;
there is rarely any benefit in setting a value other
than the default.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>transfers-in</strong></span></span></dt>
<dd>
<p>
The maximum number of inbound zone transfers
that can be running concurrently. The default value is <code class="literal">10</code>.
Increasing <span class="command"><strong>transfers-in</strong></span> may
speed up the convergence
of slave zones, but it also may increase the load on the
local system.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>transfers-out</strong></span></span></dt>
<dd>
<p>
The maximum number of outbound zone transfers
that can be running concurrently. Zone transfer requests in
excess
of the limit will be refused. The default value is <code class="literal">10</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>transfers-per-ns</strong></span></span></dt>
<dd>
<p>
The maximum number of inbound zone transfers
that can be concurrently transferring from a given remote
name server.
The default value is <code class="literal">2</code>.
Increasing <span class="command"><strong>transfers-per-ns</strong></span>
may
speed up the convergence of slave zones, but it also may
increase
the load on the remote name server. <span class="command"><strong>transfers-per-ns</strong></span> may
be overridden on a per-server basis by using the <span class="command"><strong>transfers</strong></span> phrase
of the <span class="command"><strong>server</strong></span> statement.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>transfer-source</strong></span></span></dt>
<dd>
<p><span class="command"><strong>transfer-source</strong></span>
determines which local address will be bound to IPv4
TCP connections used to fetch zones transferred
inbound by the server. It also determines the
source IPv4 address, and optionally the UDP port,
used for the refresh queries and forwarded dynamic
updates. If not set, it defaults to a system
controlled value which will usually be the address
of the interface "closest to" the remote end. This
address must appear in the remote end's
<span class="command"><strong>allow-transfer</strong></span> option for the
zone being transferred, if one is specified. This
statement sets the
<span class="command"><strong>transfer-source</strong></span> for all zones,
but can be overridden on a per-view or per-zone
basis by including a
<span class="command"><strong>transfer-source</strong></span> statement within
the <span class="command"><strong>view</strong></span> or
<span class="command"><strong>zone</strong></span> block in the configuration
file.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
Solaris 2.5.1 and earlier does not support setting the
source address for TCP sockets.
</p>
</div>
</dd>
<dt><span class="term"><span class="command"><strong>transfer-source-v6</strong></span></span></dt>
<dd>
<p>
The same as <span class="command"><strong>transfer-source</strong></span>,
except zone transfers are performed using IPv6.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>alt-transfer-source</strong></span></span></dt>
<dd>
<p>
An alternate transfer source if the one listed in
<span class="command"><strong>transfer-source</strong></span> fails and
<span class="command"><strong>use-alt-transfer-source</strong></span> is
set.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
If you do not wish the alternate transfer source
to be used, you should set
<span class="command"><strong>use-alt-transfer-source</strong></span>
appropriately and you should not depend upon
getting an answer back to the first refresh
query.
</p>
</div>
</dd>
<dt><span class="term"><span class="command"><strong>alt-transfer-source-v6</strong></span></span></dt>
<dd>
<p>
An alternate transfer source if the one listed in
<span class="command"><strong>transfer-source-v6</strong></span> fails and
<span class="command"><strong>use-alt-transfer-source</strong></span> is
set.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>use-alt-transfer-source</strong></span></span></dt>
<dd>
<p>
Use the alternate transfer sources or not. If views are
specified this defaults to <span class="command"><strong>no</strong></span>
otherwise it defaults to
<span class="command"><strong>yes</strong></span> (for BIND 8
compatibility).
</p>
</dd>
<dt><span class="term"><span class="command"><strong>notify-source</strong></span></span></dt>
<dd>
<p><span class="command"><strong>notify-source</strong></span>
determines which local source address, and
optionally UDP port, will be used to send NOTIFY
messages. This address must appear in the slave
server's <span class="command"><strong>masters</strong></span> zone clause or
in an <span class="command"><strong>allow-notify</strong></span> clause. This
statement sets the <span class="command"><strong>notify-source</strong></span>
for all zones, but can be overridden on a per-zone or
per-view basis by including a
<span class="command"><strong>notify-source</strong></span> statement within
the <span class="command"><strong>zone</strong></span> or
<span class="command"><strong>view</strong></span> block in the configuration
file.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
Solaris 2.5.1 and earlier does not support setting the
source address for TCP sockets.
</p>
</div>
</dd>
<dt><span class="term"><span class="command"><strong>notify-source-v6</strong></span></span></dt>
<dd>
<p>
Like <span class="command"><strong>notify-source</strong></span>,
but applies to notify messages sent to IPv6 addresses.
</p>
</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>
<p>
<span class="command"><strong>use-v4-udp-ports</strong></span>,
<span class="command"><strong>avoid-v4-udp-ports</strong></span>,
<span class="command"><strong>use-v6-udp-ports</strong></span>, and
<span class="command"><strong>avoid-v6-udp-ports</strong></span>
specify a list of IPv4 and IPv6 UDP ports that will be
used or not used as source ports for UDP messages.
See <a class="xref" href="Bv9ARM.ch06.html#query_address" title="Query Address">the section called “Query Address”</a> about how the
available ports are determined.
For example, with the following configuration
</p>
<pre class="programlisting">
use-v6-udp-ports { range 32768 65535; };
avoid-v6-udp-ports { 40000; range 50000 60000; };
</pre>
<p>
UDP ports of IPv6 messages sent
from <span class="command"><strong>named</strong></span> will be in one
of the following ranges: 32768 to 39999, 40001 to 49999,
and 60001 to 65535.
</p>
<p>
<span class="command"><strong>avoid-v4-udp-ports</strong></span> and
<span class="command"><strong>avoid-v6-udp-ports</strong></span> can be used
to prevent <span class="command"><strong>named</strong></span> from choosing as its random source port a
port that is blocked by your firewall or a port that is
used by other applications;
if a query went out with a source port blocked by a
firewall, the
answer would not get by the firewall and the name server would
have to query again.
Note: the desired range can also be represented only with
<span class="command"><strong>use-v4-udp-ports</strong></span> and
<span class="command"><strong>use-v6-udp-ports</strong></span>, and the
<span class="command"><strong>avoid-</strong></span> options are redundant in that
sense; they are provided for backward compatibility and
to possibly simplify the port specification.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="resource_limits"></a>Operating System Resource Limits</h4></div></div></div>
<p>
The server's usage of many system resources can be limited.
Scaled values are allowed when specifying resource limits. For
example, <span class="command"><strong>1G</strong></span> can be used instead of
<span class="command"><strong>1073741824</strong></span> to specify a limit of
one
gigabyte. <span class="command"><strong>unlimited</strong></span> requests
unlimited use, or the
maximum available amount. <span class="command"><strong>default</strong></span>
uses the limit
that was in force when the server was started. See the description
of <span class="command"><strong>size_spec</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#configuration_file_elements" title="Configuration File Elements">the section called “Configuration File Elements”</a>.
</p>
<p>
The following options set operating system resource limits for
the name server process. Some operating systems don't support
some or
any of the limits. On such systems, a warning will be issued if
the
unsupported limit is used.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>coresize</strong></span></span></dt>
<dd>
<p>
The maximum size of a core dump. The default
is <code class="literal">default</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>datasize</strong></span></span></dt>
<dd>
<p>
The maximum amount of data memory the server
may use. The default is <code class="literal">default</code>.
This is a hard limit on server memory usage.
If the server attempts to allocate memory in excess of this
limit, the allocation will fail, which may in turn leave
the server unable to perform DNS service. Therefore,
this option is rarely useful as a way of limiting the
amount of memory used by the server, but it can be used
to raise an operating system data size limit that is
too small by default. If you wish to limit the amount
of memory used by the server, use the
<span class="command"><strong>max-cache-size</strong></span> and
<span class="command"><strong>recursive-clients</strong></span>
options instead.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>files</strong></span></span></dt>
<dd>
<p>
The maximum number of files the server
may have open concurrently. The default is <code class="literal">unlimited</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>stacksize</strong></span></span></dt>
<dd>
<p>
The maximum amount of stack memory the server
may use. The default is <code class="literal">default</code>.
</p>
</dd>
</dl></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="server_resource_limits"></a>Server Resource Limits</h4></div></div></div>
<p>
The following options set limits on the server's
resource consumption that are enforced internally by the
server rather than the operating system.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>max-ixfr-log-size</strong></span></span></dt>
<dd>
<p>
This option is obsolete; it is accepted
and ignored for BIND 8 compatibility. The option
<span class="command"><strong>max-journal-size</strong></span> performs a
similar function in BIND 9.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-journal-size</strong></span></span></dt>
<dd>
<p>
Sets a maximum size for each journal file
(see <a class="xref" href="Bv9ARM.ch04.html#journal" title="The journal file">the section called “The journal file”</a>). When the journal file
approaches
the specified size, some of the oldest transactions in the
journal
will be automatically removed. The largest permitted
value is 2 gigabytes. The default is
<code class="literal">unlimited</code>, which also
means 2 gigabytes.
This may also be set on a per-zone basis.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-records</strong></span></span></dt>
<dd>
<p>
The maximum number of records permitted in a zone.
The default is zero which means unlimited.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>host-statistics-max</strong></span></span></dt>
<dd>
<p>
In BIND 8, specifies the maximum number of host statistics
entries to be kept.
Not implemented in BIND 9.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>recursive-clients</strong></span></span></dt>
<dd>
<p>
The maximum number ("hard quota") of simultaneous
recursive lookups the server will perform on behalf
of clients. The default is
<code class="literal">1000</code>. Because each recursing
client uses a fair
bit of memory (on the order of 20 kilobytes), the
value of the
<span class="command"><strong>recursive-clients</strong></span> option may
have to be decreased on hosts with limited memory.
</p>
<p>
<code class="option">recursive-clients</code> defines a "hard
quota" limit for pending recursive clients: when more
clients than this are pending, new incoming requests
will not be accepted, and for each incoming request
a previous pending request will also be dropped.
</p>
<p>
A "soft quota" is also set. When this lower
quota is exceeded, incoming requests are accepted, but
for each one, a pending request will be dropped.
If <code class="option">recursive-clients</code> is greater than
1000, the soft quota is set to
<code class="option">recursive-clients</code> minus 100;
otherwise it is set to 90% of
<code class="option">recursive-clients</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>tcp-clients</strong></span></span></dt>
<dd>
<p>
The maximum number of simultaneous client TCP
connections that the server will accept.
The default is <code class="literal">150</code>.
</p>
</dd>
<dt>
<a name="clients-per-query"></a><span class="term"><a name="cpq_term"></a><span class="command"><strong>clients-per-query</strong></span>, </span><span class="term"><span class="command"><strong>max-clients-per-query</strong></span></span>
</dt>
<dd>
<p>These set the
initial value (minimum) and maximum number of recursive
simultaneous clients for any given query
(<qname,qtype,qclass>) that the server will accept
before dropping additional clients. <span class="command"><strong>named</strong></span> will attempt to
self tune this value and changes will be logged. The
default values are 10 and 100.
</p>
<p>
This value should reflect how many queries come in for
a given name in the time it takes to resolve that name.
If the number of queries exceed this value, <span class="command"><strong>named</strong></span> will
assume that it is dealing with a non-responsive zone
and will drop additional queries. If it gets a response
after dropping queries, it will raise the estimate. The
estimate will then be lowered in 20 minutes if it has
remained unchanged.
</p>
<p>
If <span class="command"><strong>clients-per-query</strong></span> is set to zero,
then there is no limit on the number of clients per query
and no queries will be dropped.
</p>
<p>
If <span class="command"><strong>max-clients-per-query</strong></span> is set to zero,
then there is no upper bound other than imposed by
<span class="command"><strong>recursive-clients</strong></span>.
</p>
</dd>
<dt>
<a name="fetches-per-zone"></a><span class="term"><span class="command"><strong>fetches-per-zone</strong></span></span>
</dt>
<dd>
<p>
The maximum number of simultaneous iterative
queries to any one domain that the server will
permit before blocking new queries for data
in or beneath that zone.
This value should reflect how many fetches would
normally be sent to any one zone in the time it
would take to resolve them. It should be smaller
than <code class="option">recursive-clients</code>.
</p>
<p>
When many clients simultaneously query for the
same name and type, the clients will all be attached
to the same fetch, up to the
<code class="option">max-clients-per-query</code> limit,
and only one iterative query will be sent.
However, when clients are simultaneously
querying for <span class="emphasis"><em>different</em></span> names
or types, multiple queries will be sent and
<code class="option">max-clients-per-query</code> is not
effective as a limit.
</p>
<p>
Optionally, this value may be followed by the keyword
<code class="literal">drop</code> or <code class="literal">fail</code>,
indicating whether queries which exceed the fetch
quota for a zone will be dropped with no response,
or answered with SERVFAIL. The default is
<code class="literal">drop</code>.
</p>
<p>
If <span class="command"><strong>fetches-per-zone</strong></span> is set to zero,
then there is no limit on the number of fetches per query
and no queries will be dropped. The default is zero.
</p>
<p>
The current list of active fetches can be dumped by
running <span class="command"><strong>rndc recursing</strong></span>. 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.)
</p>
</dd>
<dt>
<a name="fetches-per-server"></a><span class="term"><span class="command"><strong>fetches-per-server</strong></span></span>
</dt>
<dd>
<p>
The maximum number of simultaneous iterative
queries that the server will allow to be sent to
a single upstream name server before blocking
additional queries.
This value should reflect how many fetches would
normally be sent to any one server in the time it
would take to resolve them. It should be smaller
than <code class="option">recursive-clients</code>.
</p>
<p>
Optionally, this value may be followed by the keyword
<code class="literal">drop</code> or <code class="literal">fail</code>,
indicating whether queries will be dropped with no
response, or answered with SERVFAIL, when all of the
servers authoritative for a zone are found to have
exceeded the per-server quota. The default is
<code class="literal">fail</code>.
</p>
<p>
If <span class="command"><strong>fetches-per-server</strong></span> is set to zero,
then there is no limit on the number of fetches per query
and no queries will be dropped. The default is zero.
</p>
<p>
The <span class="command"><strong>fetches-per-server</strong></span> 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 <span class="command"><strong>fetches-per-server</strong></span>
is reduced for that server. If the timeout ratio
drops below a "low" threshold, then
<span class="command"><strong>fetches-per-server</strong></span> is increased.
The <span class="command"><strong>fetch-quota-params</strong></span> options
can be used to adjust the parameters for this
calculation.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>fetch-quota-params</strong></span></span></dt>
<dd>
<p>
Sets the parameters to use for dynamic resizing of
the <code class="option">fetches-per-server</code> quota in
response to detected congestion.
</p>
<p>
The first argument is an integer value indicating
how frequently to recalculate the moving average
of the ratio of timeouts to responses for each
server. The default is 100, meaning we recalculate
the average ratio after every 100 queries have either
been answered or timed out.
</p>
<p>
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.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>reserved-sockets</strong></span></span></dt>
<dd>
<p>
The number of file descriptors reserved for TCP, stdio,
etc. This needs to be big enough to cover the number of
interfaces <span class="command"><strong>named</strong></span> listens on, <span class="command"><strong>tcp-clients</strong></span> as well as
to provide room for outgoing TCP queries and incoming zone
transfers. The default is <code class="literal">512</code>.
The minimum value is <code class="literal">128</code> and the
maximum value is <code class="literal">128</code> less than
maxsockets (-S). This option may be removed in the future.
</p>
<p>
This option has little effect on Windows.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-cache-size</strong></span></span></dt>
<dd>
<p>
The maximum amount of memory to use for the
server's cache, in bytes or % of total physical memory.
When the amount of data in the cache
reaches this limit, the server will cause records to
expire prematurely based on an LRU based strategy so
that the limit is not exceeded.
The keyword <strong class="userinput"><code>unlimited</code></strong>,
or the value 0, will place no limit on cache size;
records will be purged from the cache only when their
TTLs expire.
Any positive values less than 2MB will be ignored
and reset to 2MB.
In a server with multiple views, the limit applies
separately to the cache of each view.
The default is <strong class="userinput"><code>90%</code></strong>.
On systems where detection of amount of physical
memory is not supported values represented as %
fall back to unlimited.
Note that the detection of physical memory is done only
once at startup, so <span class="command"><strong>named</strong></span> will not
adjust the cache size if the amount of physical memory
is changed during runtime.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>tcp-listen-queue</strong></span></span></dt>
<dd>
<p>
The listen queue depth. The default and minimum is 10.
If the kernel supports the accept filter "dataready" this
also controls how
many TCP connections that will be queued in kernel space
waiting for
some data before being passed to accept. Nonzero values
less than 10 will be silently raised. A value of 0 may also
be used; on most platforms this sets the listen queue
length to a system-defined default value.
</p>
</dd>
</dl></div>
</div>
<div class="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><span class="term"><span class="command"><strong>cleaning-interval</strong></span></span></dt>
<dd>
<p>
This interval is effectively obsolete. Previously,
the server would remove expired resource records
from the cache every <span class="command"><strong>cleaning-interval</strong></span> minutes.
<acronym class="acronym">BIND</acronym> 9 now manages cache
memory in a more sophisticated manner and does not
rely on the periodic cleaning any more.
Specifying this option therefore has no effect on
the server's behavior.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>heartbeat-interval</strong></span></span></dt>
<dd>
<p>
The server will perform zone maintenance tasks
for all zones marked as <span class="command"><strong>dialup</strong></span> whenever this
interval expires. The default is 60 minutes. Reasonable
values are up
to 1 day (1440 minutes). The maximum value is 28 days
(40320 minutes).
If set to 0, no zone maintenance for these zones will occur.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>interface-interval</strong></span></span></dt>
<dd>
<p>
The server will scan the network interface list
every <span class="command"><strong>interface-interval</strong></span>
minutes. The default
is 60 minutes. The maximum value is 28 days (40320 minutes).
If set to 0, interface scanning will only occur when
the configuration file is loaded. After the scan, the
server will
begin listening for queries on any newly discovered
interfaces (provided they are allowed by the
<span class="command"><strong>listen-on</strong></span> configuration), and
will
stop listening on interfaces that have gone away.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>statistics-interval</strong></span></span></dt>
<dd>
<p>
Name server statistics will be logged
every <span class="command"><strong>statistics-interval</strong></span>
minutes. The default is
60. The maximum value is 28 days (40320 minutes).
If set to 0, no statistics will be logged.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
Not yet implemented in
<acronym class="acronym">BIND</acronym> 9.
</p>
</div>
</dd>
<dt><span class="term"><span class="command"><strong>topology</strong></span></span></dt>
<dd>
<p>
In BIND 8, this option indicated network topology
so that preferential treatment could be given to
the topologicaly closest name servers when sending
queries. It is not implemented in BIND 9.
</p>
</dd>
</dl></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="the_sortlist_statement"></a>The <span class="command"><strong>sortlist</strong></span> Statement</h4></div></div></div>
<p>
The response to a DNS query may consist of multiple resource
records (RRs) forming a resource record set (RRset). The name
server will normally return the RRs within the RRset in an
indeterminate order (but see the <span class="command"><strong>rrset-order</strong></span>
statement in <a class="xref" href="Bv9ARM.ch06.html#rrset_ordering" title="RRset Ordering">the section called “RRset Ordering”</a>). The client
resolver code should rearrange the RRs as appropriate, that is,
using any addresses on the local net in preference to other
addresses. However, not all resolvers can do this or are
correctly configured. When a client is using a local server,
the sorting can be performed in the server, based on the
client's address. This only requires configuring the name
servers, not all the clients.
</p>
<p>
The <span class="command"><strong>sortlist</strong></span> statement (see below) takes an
<span class="command"><strong>address_match_list</strong></span> and interprets it in a
special way. Each top level statement in the
<span class="command"><strong>sortlist</strong></span> must itself be an explicit
<span class="command"><strong>address_match_list</strong></span> with one or two elements.
The first element (which may be an IP address, an IP prefix, an
ACL name or a nested <span class="command"><strong>address_match_list</strong></span>) of
each top level list is checked against the source address of
the query until a match is found.
</p>
<p>
Once the source address of the query has been matched, if the
top level statement contains only one element, the actual
primitive element that matched the source address is used to
select the address in the response to move to the beginning of
the response. If the statement is a list of two elements, then
the second element is 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.
</p>
<p>
In the following example, any queries received from any of the
addresses of the host itself will get responses preferring
addresses on any of the locally connected networks. Next most
preferred are addresses on the 192.168.1/24 network, and after
that either the 192.168.2/24 or 192.168.3/24 network with no
preference shown between these two networks. Queries received
from a host on the 192.168.1/24 network will prefer other
addresses on that network to the 192.168.2/24 and 192.168.3/24
networks. Queries received from a host on the 192.168.4/24 or
the 192.168.5/24 network will only prefer other addresses on
their directly connected networks.
</p>
<pre class="programlisting">sortlist {
// IF the local host
// THEN first fit on the following nets
{ localhost;
{ localnets;
192.168.1/24;
{ 192.168.2/24; 192.168.3/24; }; }; };
// IF on class C 192.168.1 THEN use .1, or .2 or .3
{ 192.168.1/24;
{ 192.168.1/24;
{ 192.168.2/24; 192.168.3/24; }; }; };
// IF on class C 192.168.2 THEN use .2, or .1 or .3
{ 192.168.2/24;
{ 192.168.2/24;
{ 192.168.1/24; 192.168.3/24; }; }; };
// IF on class C 192.168.3 THEN use .3, or .1 or .2
{ 192.168.3/24;
{ 192.168.3/24;
{ 192.168.1/24; 192.168.2/24; }; }; };
// IF .4 or .5 THEN prefer that net
{ { 192.168.4/24; 192.168.5/24; };
};
};</pre>
<p>
The following example will give reasonable behavior for the
local host and hosts on directly connected networks. It is
similar to the behavior of the address sort in
<acronym class="acronym">BIND</acronym> 4.9.x. Responses sent to queries from
the local host will favor any of the directly connected
networks. Responses sent to queries from any other hosts on a
directly connected network will prefer addresses on that same
network. Responses to other queries will not be sorted.
</p>
<pre class="programlisting">sortlist {
{ localhost; localnets; };
{ localnets; };
};
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="rrset_ordering"></a>RRset Ordering</h4></div></div></div>
<p>
When multiple records are returned in an answer it may be
useful to configure the order of the records placed into the
response.
The <span class="command"><strong>rrset-order</strong></span> statement permits
configuration
of the ordering of the records in a multiple record response.
See also the <span class="command"><strong>sortlist</strong></span> statement,
<a class="xref" href="Bv9ARM.ch06.html#the_sortlist_statement" title="The sortlist Statement">the section called “The <span class="command"><strong>sortlist</strong></span> Statement”</a>.
</p>
<p>
An <span class="command"><strong>order_spec</strong></span> is defined as
follows:
</p>
<p>
[<span class="optional">class <em class="replaceable"><code>class_name</code></em></span>]
[<span class="optional">type <em class="replaceable"><code>type_name</code></em></span>]
[<span class="optional">name <em class="replaceable"><code>"domain_name"</code></em></span>]
order <em class="replaceable"><code>ordering</code></em>
</p>
<p>
If no class is specified, the default is <span class="command"><strong>ANY</strong></span>.
If no type is specified, the default is <span class="command"><strong>ANY</strong></span>.
If no name is specified, the default is "<span class="command"><strong>*</strong></span>" (asterisk).
</p>
<p>
The legal values for <span class="command"><strong>ordering</strong></span> are:
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="0.750in" class="1">
<col width="3.750in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p><span class="command"><strong>fixed</strong></span></p>
</td>
<td>
<p>
Records are returned in the order they
are defined in the zone file.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>random</strong></span></p>
</td>
<td>
<p>
Records are returned in some random order.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>cyclic</strong></span></p>
</td>
<td>
<p>
Records are returned in a cyclic round-robin order.
</p>
<p>
If <acronym class="acronym">BIND</acronym> is configured with the
"--enable-fixed-rrset" option at compile time, then
the initial ordering of the RRset will match the
one specified in the zone file.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
For example:
</p>
<pre class="programlisting">rrset-order {
class IN type A name "host.example.com" order random;
order cyclic;
};
</pre>
<p>
will cause any responses for type A records in class IN that
have "<code class="literal">host.example.com</code>" as a
suffix, to always be returned
in random order. All other records are returned in cyclic order.
</p>
<p>
If multiple <span class="command"><strong>rrset-order</strong></span> statements
appear, they are not combined — the last one applies.
</p>
<p>
By default, all records are returned in random order.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
In this release of <acronym class="acronym">BIND</acronym> 9, the
<span class="command"><strong>rrset-order</strong></span> statement does not support
"fixed" ordering by default. Fixed ordering can be enabled
at compile time by specifying "--enable-fixed-rrset" on
the "configure" command line.
</p>
</div>
</div>
<div class="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><span class="term"><span class="command"><strong>lame-ttl</strong></span></span></dt>
<dd>
<p>
Sets the number of seconds to cache a
lame server indication. 0 disables caching. (This is
<span class="bold"><strong>NOT</strong></span> recommended.)
The default is <code class="literal">600</code> (10 minutes) and the
maximum value is
<code class="literal">1800</code> (30 minutes).
</p>
</dd>
<dt><span class="term"><span class="command"><strong>servfail-ttl</strong></span></span></dt>
<dd>
<p>
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.
</p>
<p>
The maximum value is <code class="literal">30</code>
seconds; any higher value will be silently
reduced. The default is <code class="literal">1</code>
second.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-ncache-ttl</strong></span></span></dt>
<dd>
<p>
To reduce network traffic and increase performance,
the server stores negative answers. <span class="command"><strong>max-ncache-ttl</strong></span> is
used to set a maximum retention time for these answers in
the server
in seconds. The default
<span class="command"><strong>max-ncache-ttl</strong></span> is <code class="literal">10800</code> seconds (3 hours).
<span class="command"><strong>max-ncache-ttl</strong></span> cannot exceed
7 days and will
be silently truncated to 7 days if set to a greater value.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-cache-ttl</strong></span></span></dt>
<dd>
<p>
Sets the maximum time for which the server will
cache ordinary (positive) answers in seconds.
The default is 604800 (one week).
A value of zero may cause all queries to return
SERVFAIL, because of lost caches of intermediate
RRsets (such as NS and glue AAAA/A records) in the
resolution process.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>min-roots</strong></span></span></dt>
<dd>
<p>
The minimum number of root servers that
is required for a request for the root servers to be
accepted. The default
is <strong class="userinput"><code>2</code></strong>.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
Not implemented in <acronym class="acronym">BIND</acronym> 9.
</p>
</div>
</dd>
<dt><span class="term"><span class="command"><strong>sig-validity-interval</strong></span></span></dt>
<dd>
<p>
Specifies the number of days into the future when
DNSSEC signatures automatically generated as a
result of dynamic updates (<a class="xref" href="Bv9ARM.ch04.html#dynamic_update" title="Dynamic Update">the section called “Dynamic Update”</a>) will expire. There
is an optional second field which specifies how
long before expiry that the signatures will be
regenerated. If not specified, the signatures will
be regenerated at 1/4 of base interval. The second
field is specified in days if the base interval is
greater than 7 days otherwise it is specified in hours.
The default base interval is <code class="literal">30</code> days
giving a re-signing interval of 7 1/2 days. The maximum
values are 10 years (3660 days).
</p>
<p>
The signature inception time is unconditionally
set to one hour before the current time to allow
for a limited amount of clock skew.
</p>
<p>
The <span class="command"><strong>sig-validity-interval</strong></span>
should be, at least, several multiples of the SOA
expire interval to allow for reasonable interaction
between the various timer and expiry dates.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>sig-signing-nodes</strong></span></span></dt>
<dd>
<p>
Specify the maximum number of nodes to be
examined in each quantum when signing a zone with
a new DNSKEY. The default is
<code class="literal">100</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>sig-signing-signatures</strong></span></span></dt>
<dd>
<p>
Specify a threshold number of signatures that
will terminate processing a quantum when signing
a zone with a new DNSKEY. The default is
<code class="literal">10</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>sig-signing-type</strong></span></span></dt>
<dd>
<p>
Specify a private RDATA type to be used when generating
signing state records. The default is
<code class="literal">65534</code>.
</p>
<p>
It is expected that this parameter may be removed
in a future version once there is a standard type.
</p>
<p>
Signing state records are used to internally by
<span class="command"><strong>named</strong></span> to track the current state of
a zone-signing process, i.e., whether it is still active
or has been completed. The records can be inspected
using the command
<span class="command"><strong>rndc signing -list <em class="replaceable"><code>zone</code></em></strong></span>.
Once <span class="command"><strong>named</strong></span> has finished signing
a zone with a particular key, the signing state
record associated with that key can be removed from
the zone by running
<span class="command"><strong>rndc signing -clear <em class="replaceable"><code>keyid/algorithm</code></em> <em class="replaceable"><code>zone</code></em></strong></span>.
To clear all of the completed signing state
records for a zone, use
<span class="command"><strong>rndc signing -clear all <em class="replaceable"><code>zone</code></em></strong></span>.
</p>
</dd>
<dt>
<span class="term"><span class="command"><strong>min-refresh-time</strong></span>, </span><span class="term"><span class="command"><strong>max-refresh-time</strong></span>, </span><span class="term"><span class="command"><strong>min-retry-time</strong></span>, </span><span class="term"><span class="command"><strong>max-retry-time</strong></span></span>
</dt>
<dd>
<p>
These options control the server's behavior on refreshing a
zone (querying for SOA changes) or retrying failed
transfers. Usually the SOA values for the zone are used,
up to a hard-coded maximum expiry of 24 weeks. However,
these values are set by the master, giving slave server
administrators little control over their contents.
</p>
<p>
These options allow the administrator to set a minimum and
maximum refresh and retry time in seconds per-zone,
per-view, or globally. These options are valid for
slave and stub zones, and clamp the SOA refresh and
retry times to the specified values.
</p>
<p>
The following defaults apply.
<span class="command"><strong>min-refresh-time</strong></span> 300 seconds,
<span class="command"><strong>max-refresh-time</strong></span> 2419200 seconds
(4 weeks), <span class="command"><strong>min-retry-time</strong></span> 500 seconds,
and <span class="command"><strong>max-retry-time</strong></span> 1209600 seconds
(2 weeks).
</p>
</dd>
<dt><span class="term"><span class="command"><strong>edns-udp-size</strong></span></span></dt>
<dd>
<p>
Sets the maximum advertised EDNS UDP buffer size in
bytes, to control the size of packets received from
authoritative servers in response to recursive queries.
Valid values are 512 to 4096 (values outside this range
will be silently adjusted to the nearest value within
it). The default value is 4096.
</p>
<p>
The usual reason for setting
<span class="command"><strong>edns-udp-size</strong></span> to a non-default value
is to get UDP answers to pass through broken firewalls
that block fragmented packets and/or block UDP DNS
packets that are greater than 512 bytes.
</p>
<p>
When <span class="command"><strong>named</strong></span> first queries a remote
server, it will advertise a UDP buffer size of 512, as
this has the greatest chance of success on the first try.
</p>
<p>
If the initial response times out, <span class="command"><strong>named</strong></span>
will try again with plain DNS, and if that is successful,
it will be taken as evidence that the server does not
support EDNS. After enough failures using EDNS and
successes using plain DNS, <span class="command"><strong>named</strong></span>
will default to plain DNS for future communications
with that server. (Periodically, <span class="command"><strong>named</strong></span>
will send an EDNS query to see if the situation has
improved.)
</p>
<p>
However, if the initial query is successful with
EDNS advertising a buffer size of 512, then
<span class="command"><strong>named</strong></span> will advertise progressively
larger buffer sizes on successive queries, until
responses begin timing out or
<span class="command"><strong>edns-udp-size</strong></span> is reached.
</p>
<p>
The default buffer sizes used by <span class="command"><strong>named</strong></span>
are 512, 1232, 1432, and 4096, but never exceeding
<span class="command"><strong>edns-udp-size</strong></span>. (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.)
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-udp-size</strong></span></span></dt>
<dd>
<p>
Sets the maximum EDNS UDP message size
<span class="command"><strong>named</strong></span> will send in bytes.
Valid values are 512 to 4096 (values outside this
range will be silently adjusted to the nearest
value within it). The default value is 4096.
</p>
<p>
This value applies to responses sent by a server; to
set the advertised buffer size in queries, see
<span class="command"><strong>edns-udp-size</strong></span>.
</p>
<p>
The usual reason for setting
<span class="command"><strong>max-udp-size</strong></span> to a non-default
value is to get UDP answers to pass through broken
firewalls that block fragmented packets and/or
block UDP packets that are greater than 512 bytes.
This is independent of the advertised receive
buffer (<span class="command"><strong>edns-udp-size</strong></span>).
</p>
<p>
Setting this to a low value will encourage additional
TCP traffic to the nameserver.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>masterfile-format</strong></span></span></dt>
<dd>
<p>Specifies
the file format of zone files (see
<a class="xref" href="Bv9ARM.ch06.html#zonefile_format" title="Additional File Formats">the section called “Additional File Formats”</a>).
The default value is <code class="constant">text</code>, which is the
standard textual representation, except for slave zones,
in which the default value is <code class="constant">raw</code>.
Files in other formats than <code class="constant">text</code> are
typically expected to be generated by the
<span class="command"><strong>named-compilezone</strong></span> tool, or dumped by
<span class="command"><strong>named</strong></span>.
</p>
<p>
Note that when a zone file in a different format than
<code class="constant">text</code> is loaded, <span class="command"><strong>named</strong></span>
may omit some of the checks which would be performed for a
file in the <code class="constant">text</code> format. In particular,
<span class="command"><strong>check-names</strong></span> checks do not apply
for the <code class="constant">raw</code> format. This means
a zone file in the <code class="constant">raw</code> format
must be generated with the same check level as that
specified in the <span class="command"><strong>named</strong></span> configuration
file. Also, <code class="constant">map</code> format files are
loaded directly into memory via memory mapping, with only
minimal checking.
</p>
<p>
This statement sets the
<span class="command"><strong>masterfile-format</strong></span> for all zones,
but can be overridden on a per-zone or per-view basis
by including a <span class="command"><strong>masterfile-format</strong></span>
statement within the <span class="command"><strong>zone</strong></span> or
<span class="command"><strong>view</strong></span> block in the configuration
file.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>masterfile-style</strong></span></span></dt>
<dd>
<p>
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>.)
</p>
<p>
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>.
</p>
</dd>
<dt>
<a name="max-recursion-depth"></a><span class="term"><span class="command"><strong>max-recursion-depth</strong></span></span>
</dt>
<dd>
<p>
Sets the maximum number of levels of recursion
that are permitted at any one time while servicing
a recursive query. Resolving a name may require
looking up a name server address, which in turn
requires resolving another name, etc; if the number
of indirections exceeds this value, the recursive
query is terminated and returns SERVFAIL. The
default is 7.
</p>
</dd>
<dt>
<a name="max-recursion-queries"></a><span class="term"><span class="command"><strong>max-recursion-queries</strong></span></span>
</dt>
<dd>
<p>
Sets the maximum number of iterative queries that
may be sent while servicing a recursive query.
If more queries are sent, the recursive query
is terminated and returns SERVFAIL. Queries to
look up top level domains such as "com" and "net"
and the DNS root zone are exempt from this limitation.
The default is 75.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>notify-delay</strong></span></span></dt>
<dd>
<p>
The delay, in seconds, between sending sets of notify
messages for a zone. The default is five (5) seconds.
</p>
<p>
The overall rate that NOTIFY messages are sent for all
zones is controlled by <span class="command"><strong>serial-query-rate</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-rsa-exponent-size</strong></span></span></dt>
<dd>
<p>
The maximum RSA exponent size, in bits, that will
be accepted when validating. Valid values are 35
to 4096 bits. The default zero (0) is also accepted
and is equivalent to 4096.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>prefetch</strong></span></span></dt>
<dd>
<p>
When a query is received for cached data which
is to expire shortly, <span class="command"><strong>named</strong></span> can
refresh the data from the authoritative server
immediately, ensuring that the cache always has an
answer available.
</p>
<p>
The <code class="option">prefetch</code> specifies the
"trigger" TTL value at which prefetch of the current
query will take place: when a cache record with a
lower TTL value is encountered during query processing,
it will be refreshed. Valid trigger TTL values are 1 to
10 seconds. Values larger than 10 seconds will be silently
reduced to 10.
Setting a trigger TTL to zero (0) causes
prefetch to be disabled.
The default trigger TTL is <code class="literal">2</code>.
</p>
<p>
An optional second argument specifies the "eligibility"
TTL: the smallest <span class="emphasis"><em>original</em></span>
TTL value that will be accepted for a record to be
eligible for prefetching. The eligibility TTL must
be at least six seconds longer than the trigger TTL;
if it isn't, <span class="command"><strong>named</strong></span> will silently
adjust it upward.
The default eligibility TTL is <code class="literal">9</code>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>v6-bias</strong></span></span></dt>
<dd>
<p>
When determining the next nameserver to try
preference IPv6 nameservers by this many milliseconds.
The default is <code class="literal">50</code> milliseconds.
</p>
</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>
<p>
The server provides some helpful diagnostic information
through a number of built-in zones under the
pseudo-top-level-domain <code class="literal">bind</code> in the
<span class="command"><strong>CHAOS</strong></span> 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 “<span class="command"><strong>view</strong></span> Statement Grammar”</a>) of
class
<span class="command"><strong>CHAOS</strong></span> which is separate from the
default view of class <span class="command"><strong>IN</strong></span>. Most global
configuration options (<span class="command"><strong>allow-query</strong></span>,
etc) will apply to this view, but some are locally
overridden: <span class="command"><strong>notify</strong></span>,
<span class="command"><strong>recursion</strong></span> and
<span class="command"><strong>allow-new-zones</strong></span> are
always set to <strong class="userinput"><code>no</code></strong>, and
<span class="command"><strong>rate-limit</strong></span> is set to allow
three responses per second.
</p>
<p>
If you need to disable these zones, use the options
below, or hide the built-in <span class="command"><strong>CHAOS</strong></span>
view by
defining an explicit view of class <span class="command"><strong>CHAOS</strong></span>
that matches all clients.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>version</strong></span></span></dt>
<dd>
<p>
The version the server should report
via a query of the name <code class="literal">version.bind</code>
with type <span class="command"><strong>TXT</strong></span>, class <span class="command"><strong>CHAOS</strong></span>.
The default is the real version number of this server.
Specifying <span class="command"><strong>version none</strong></span>
disables processing of the queries.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>hostname</strong></span></span></dt>
<dd>
<p>
The hostname the server should report via a query of
the name <code class="filename">hostname.bind</code>
with type <span class="command"><strong>TXT</strong></span>, class <span class="command"><strong>CHAOS</strong></span>.
This defaults to the hostname of the machine hosting the
name server as
found by the gethostname() function. The primary purpose of such queries
is to
identify which of a group of anycast servers is actually
answering your queries. Specifying <span class="command"><strong>hostname none;</strong></span>
disables processing of the queries.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>server-id</strong></span></span></dt>
<dd>
<p>
The ID the server should report when receiving a Name
Server Identifier (NSID) query, or a query of the name
<code class="filename">ID.SERVER</code> with type
<span class="command"><strong>TXT</strong></span>, class <span class="command"><strong>CHAOS</strong></span>.
The primary purpose of such queries is to
identify which of a group of anycast servers is actually
answering your queries. Specifying <span class="command"><strong>server-id none;</strong></span>
disables processing of the queries.
Specifying <span class="command"><strong>server-id hostname;</strong></span> will cause <span class="command"><strong>named</strong></span> to
use the hostname as found by the gethostname() function.
The default <span class="command"><strong>server-id</strong></span> is <span class="command"><strong>none</strong></span>.
</p>
</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>
<p>
The <span class="command"><strong>named</strong></span> server has some built-in
empty zones (SOA and NS records only).
These are for zones that should normally be answered locally
and which queries should not be sent to the Internet's root
servers. The official servers which cover these namespaces
return NXDOMAIN responses to these queries. In particular,
these cover the reverse namespaces for addresses from
RFC 1918, RFC 4193, RFC 5737 and RFC 6598. They also include the
reverse namespace for IPv6 local address (locally assigned),
IPv6 link local addresses, the IPv6 loopback address and the
IPv6 unknown address.
</p>
<p>
The server will attempt to determine if a built-in zone
already exists or is active (covered by a forward-only
forwarding declaration) and will not create an empty
zone in that case.
</p>
<p>
The current list of empty zones is:
</p>
<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>
<p>
</p>
<p>
Empty zones are settable at the view level and only apply to
views of class IN. Disabled empty zones are only inherited
from options if there are no disabled empty zones specified
at the view level. To override the options list of disabled
zones, you can disable the root zone at the view level, for example:
</p>
<pre class="programlisting">
disable-empty-zone ".";
</pre>
<p>
</p>
<p>
If you are using the address ranges covered here, you should
already have reverse zones covering the addresses you use.
In practice this appears to not be the case with many queries
being made to the infrastructure servers for names in these
spaces. So many in fact that sacrificial servers were needed
to be deployed to channel the query load away from the
infrastructure servers.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
The real parent servers for these zones should disable all
empty zone under the parent zone they serve. For the real
root servers, this is all built-in empty zones. This will
enable them to return referrals to deeper in the tree.
</p>
</div>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>empty-server</strong></span></span></dt>
<dd>
<p>
Specify what server name will appear in the returned
SOA record for empty zones. If none is specified, then
the zone's name will be used.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>empty-contact</strong></span></span></dt>
<dd>
<p>
Specify what contact name will appear in the returned
SOA record for empty zones. If none is specified, then
"." will be used.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>empty-zones-enable</strong></span></span></dt>
<dd>
<p>
Enable or disable all empty zones. By default, they
are enabled.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>disable-empty-zone</strong></span></span></dt>
<dd>
<p>
Disable individual empty zones. By default, none are
disabled. This option can be specified multiple times.
</p>
</dd>
</dl></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="acache"></a>Additional Section Caching</h4></div></div></div>
<p>
The additional section cache, also called <span class="command"><strong>acache</strong></span>,
is an internal cache to improve the response performance of BIND 9.
When additional section caching is enabled, BIND 9 will
cache an internal short-cut to the additional section content for
each answer RR.
Note that <span class="command"><strong>acache</strong></span> is an internal caching
mechanism of BIND 9, and is not related to the DNS caching
server function.
</p>
<p>
Additional section caching does not change the
response content (except the RRsets ordering of the additional
section, see below), but can improve the response performance
significantly.
It is particularly effective when BIND 9 acts as an authoritative
server for a zone that has many delegations with many glue RRs.
</p>
<p>
In order to obtain the maximum performance improvement
from additional section caching, setting
<span class="command"><strong>additional-from-cache</strong></span>
to <span class="command"><strong>no</strong></span> is recommended, since the current
implementation of <span class="command"><strong>acache</strong></span>
does not short-cut of additional section information from the
DNS cache data.
</p>
<p>
One obvious disadvantage of <span class="command"><strong>acache</strong></span> is
that it requires much more
memory for the internal cached data.
Thus, if the response performance does not matter and memory
consumption is much more critical, the
<span class="command"><strong>acache</strong></span> mechanism can be
disabled by setting <span class="command"><strong>acache-enable</strong></span> to
<span class="command"><strong>no</strong></span>.
It is also possible to specify the upper limit of memory
consumption
for acache by using <span class="command"><strong>max-acache-size</strong></span>.
</p>
<p>
Additional section caching also has a minor effect on the
RRset ordering in the additional section.
Without <span class="command"><strong>acache</strong></span>,
<span class="command"><strong>cyclic</strong></span> order is effective for the additional
section as well as the answer and authority sections.
However, additional section caching fixes the ordering when it
first caches an RRset for the additional section, and the same
ordering will be kept in succeeding responses, regardless of the
setting of <span class="command"><strong>rrset-order</strong></span>.
The effect of this should be minor, however, since an
RRset in the additional section
typically only contains a small number of RRs (and in many cases
it only contains a single RR), in which case the
ordering does not matter much.
</p>
<p>
The following is a summary of options related to
<span class="command"><strong>acache</strong></span>.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>acache-enable</strong></span></span></dt>
<dd>
<p>
If <span class="command"><strong>yes</strong></span>, additional section caching is
enabled. The default value is <span class="command"><strong>no</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>acache-cleaning-interval</strong></span></span></dt>
<dd>
<p>
The server will remove stale cache entries, based on an LRU
based
algorithm, every <span class="command"><strong>acache-cleaning-interval</strong></span> minutes.
The default is 60 minutes.
If set to 0, no periodic cleaning will occur.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-acache-size</strong></span></span></dt>
<dd>
<p>
The maximum amount of memory in bytes to use for the server's acache.
When the amount of data in the acache reaches this limit,
the server
will clean more aggressively so that the limit is not
exceeded.
In a server with multiple views, the limit applies
separately to the
acache of each view.
The default is <code class="literal">16M</code>.
</p>
</dd>
</dl></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="content_filtering"></a>Content Filtering</h4></div></div></div>
<p>
<acronym class="acronym">BIND</acronym> 9 provides the ability to filter
out DNS responses from external DNS servers containing
certain types of data in the answer section.
Specifically, it can reject address (A or AAAA) records if
the corresponding IPv4 or IPv6 addresses match the given
<code class="varname">address_match_list</code> of the
<span class="command"><strong>deny-answer-addresses</strong></span> option.
It can also reject CNAME or DNAME records if the "alias"
name (i.e., the CNAME alias or the substituted query name
due to DNAME) matches the
given <code class="varname">namelist</code> of the
<span class="command"><strong>deny-answer-aliases</strong></span> option, where
"match" means the alias name is a subdomain of one of
the <code class="varname">name_list</code> elements.
If the optional <code class="varname">namelist</code> is specified
with <span class="command"><strong>except-from</strong></span>, records whose query name
matches the list will be accepted regardless of the filter
setting.
Likewise, if the alias name is a subdomain of the
corresponding zone, the <span class="command"><strong>deny-answer-aliases</strong></span>
filter will not apply;
for example, even if "example.com" is specified for
<span class="command"><strong>deny-answer-aliases</strong></span>,
</p>
<pre class="programlisting">www.example.com. CNAME xxx.example.com.</pre>
<p>
returned by an "example.com" server will be accepted.
</p>
<p>
In the <code class="varname">address_match_list</code> of the
<span class="command"><strong>deny-answer-addresses</strong></span> option, only
<code class="varname">ip_addr</code>
and <code class="varname">ip_prefix</code>
are meaningful;
any <code class="varname">key_id</code> will be silently ignored.
</p>
<p>
If a response message is rejected due to the filtering,
the entire message is discarded without being cached, and
a SERVFAIL error will be returned to the client.
</p>
<p>
This filtering is intended to prevent "DNS rebinding attacks," in
which an attacker, in response to a query for a domain name the
attacker controls, returns an IP address within your own network or
an alias name within your own domain.
A naive web browser or script could then serve as an
unintended proxy, allowing the attacker
to get access to an internal node of your local network
that couldn't be externally accessed otherwise.
See the paper available at
<a class="link" href="http://portal.acm.org/citation.cfm?id=1315245.1315298" target="_top">
http://portal.acm.org/citation.cfm?id=1315245.1315298
</a>
for more details about the attacks.
</p>
<p>
For example, if you own a domain named "example.net" and
your internal network uses an IPv4 prefix 192.0.2.0/24,
you might specify the following rules:
</p>
<pre class="programlisting">deny-answer-addresses { 192.0.2.0/24; } except-from { "example.net"; };
deny-answer-aliases { "example.net"; };
</pre>
<p>
If an external attacker lets a web browser in your local
network look up an IPv4 address of "attacker.example.com",
the attacker's DNS server would return a response like this:
</p>
<pre class="programlisting">attacker.example.com. A 192.0.2.1</pre>
<p>
in the answer section.
Since the rdata of this record (the IPv4 address) matches
the specified prefix 192.0.2.0/24, this response will be
ignored.
</p>
<p>
On the other hand, if the browser looks up a legitimate
internal web server "www.example.net" and the
following response is returned to
the <acronym class="acronym">BIND</acronym> 9 server
</p>
<pre class="programlisting">www.example.net. A 192.0.2.2</pre>
<p>
it will be accepted since the owner name "www.example.net"
matches the <span class="command"><strong>except-from</strong></span> element,
"example.net".
</p>
<p>
Note that this is not really an attack on the DNS per se.
In fact, there is nothing wrong for an "external" name to
be mapped to your "internal" IP address or domain name
from the DNS point of view.
It might actually be provided for a legitimate purpose,
such as for debugging.
As long as the mapping is provided by the correct owner,
it is not possible or does not make sense to detect
whether the intent of the mapping is legitimate or not
within the DNS.
The "rebinding" attack must primarily be protected at the
application that uses the DNS.
For a large site, however, it may be difficult to protect
all possible applications at once.
This filtering feature is provided only to help such an
operational environment;
it is generally discouraged to turn it on unless you are
very sure you have no other choice and the attack is a
real threat for your applications.
</p>
<p>
Care should be particularly taken if you want to use this
option for addresses within 127.0.0.0/8.
These addresses are obviously "internal", but many
applications conventionally rely on a DNS mapping from
some name to such an address.
Filtering out DNS records containing this address
spuriously can break such applications.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="rpz"></a>Response Policy Zone (RPZ) Rewriting</h4></div></div></div>
<p>
<acronym class="acronym">BIND</acronym> 9 includes a limited
mechanism to modify DNS responses for requests
analogous to email anti-spam DNS blacklists.
Responses can be changed to deny the existence of domains (NXDOMAIN),
deny the existence of IP addresses for domains (NODATA),
or contain other IP addresses or data.
</p>
<p>
Response policy zones are named in the
<span class="command"><strong>response-policy</strong></span> 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
<span class="command"><strong>allow-query { localhost; };</strong></span>.
Note that zones using <span class="command"><strong>masterfile-format map</strong></span>
cannot be used as policy zones.
</p>
<p>
A <span class="command"><strong>response-policy</strong></span> 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 <span class="command"><strong>response-policy</strong></span> option; more
than that is a configuration error.
</p>
<p>
Five policy triggers can be encoded in RPZ records.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>RPZ-CLIENT-IP</strong></span></span></dt>
<dd>
<p>
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
<span class="command"><strong>rpz-client-ip</strong></span> relativized to the
policy zone origin name
and encode an address or address block.
IPv4 addresses are represented as
<strong class="userinput"><code>prefixlength.B4.B3.B2.B1.rpz-client-ip</code></strong>.
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.
</p>
<p>
IPv6 addresses are encoded in a format similar
to the standard IPv6 text representation,
<strong class="userinput"><code>prefixlength.W8.W7.W6.W5.W4.W3.W2.W1.rpz-client-ip</code></strong>.
Each of W8,...,W1 is a one to four digit hexadecimal number
representing 16 bits of the IPv6 address as in the standard
text representation of IPv6 addresses, but reversed as in
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 <strong class="userinput"><code>.zz.</code></strong>
analogous to double colons (::) in standard IPv6 text
encodings.
The IPv6 prefix length must be between 1 and 128.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>QNAME</strong></span></span></dt>
<dd>
<p>
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.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>RPZ-IP</strong></span></span></dt>
<dd>
<p>
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 <span class="command"><strong>rpz-ip</strong></span>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>RPZ-NSDNAME</strong></span></span></dt>
<dd>
<p>
NSDNAME triggers match names of authoritative servers
for the query name, a parent of the query name, a CNAME for
query name, or a parent of a CNAME.
They are encoded as subdomains of
<span class="command"><strong>rpz-nsdname</strong></span> 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.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>RPZ-NSIP</strong></span></span></dt>
<dd>
<p>
NSIP triggers match the IP addresses of authoritative
servers. They are enncoded like IP triggers, except as
subdomains of <span class="command"><strong>rpz-nsip</strong></span>.
NSDNAME and NSIP triggers are checked only for names with at
least <span class="command"><strong>min-ns-dots</strong></span> dots.
The default value of <span class="command"><strong>min-ns-dots</strong></span> is
1, to exclude top level domains.
</p>
<p>
If a name server's IP address is not yet known,
<span class="command"><strong>named</strong></span> will recursively look up
the IP address before applying an RPZ-NSIP rule.
This can cause a processing delay. To speed up
processing at the cost of precision, the
<span class="command"><strong>nsip-wait-recurse</strong></span> option
can be used: when set to <strong class="userinput"><code>no</code></strong>,
RPZ-NSIP rules will only be applied when a name
servers's IP address has already been looked up and
cached. If a server's IP address is not in the
cache, then the RPZ-NSIP rule will be ignored,
but the address will be looked up in the
background, and the rule will be applied
to subsequent queries. The default is
<strong class="userinput"><code>yes</code></strong>, meaning RPZ-NSIP
rules should always be applied even if an
address needs to be looked up first.
</p>
</dd>
</dl></div>
<p>
</p>
<p>
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
<span class="command"><strong>DISABLED</strong></span> actions) must be chosen.
Triggers or the records that encode them are chosen for the
rewriting in the following order:
</p>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">Choose the triggered record in the zone that appears
first in the <span class="command"><strong>response-policy</strong></span> 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>
<p>
</p>
<p>
When the processing of a response is restarted to resolve
DNAME or CNAME records and a policy record set has
not been triggered,
all response policy zones are again consulted for the
DNAME or CNAME names and addresses.
</p>
<p>
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 <span class="command"><strong>TCP-only</strong></span> policy is
commonly used with <span class="command"><strong>client-IP</strong></span> triggers,
it can be used with any type of trigger to force the use of
TCP for responses with owner names in a zone.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>PASSTHRU</strong></span></span></dt>
<dd>
<p>
The whitelist policy is specified
by a CNAME whose target is <span class="command"><strong>rpz-passthru</strong></span>.
It causes the response to not be rewritten
and is most often used to "poke holes" in policies for
CIDR blocks.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>DROP</strong></span></span></dt>
<dd>
<p>
The blacklist policy is specified
by a CNAME whose target is <span class="command"><strong>rpz-drop</strong></span>.
It causes the response to be discarded.
Nothing is sent to the DNS client.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>TCP-Only</strong></span></span></dt>
<dd>
<p>
The "slip" policy is specified
by a CNAME whose target is <span class="command"><strong>rpz-tcp-only</strong></span>.
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.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>NXDOMAIN</strong></span></span></dt>
<dd>
<p>
The domain undefined response is encoded
by a CNAME whose target is the root domain (.)
</p>
</dd>
<dt><span class="term"><span class="command"><strong>NODATA</strong></span></span></dt>
<dd>
<p>
The empty set of resource records is specified by
CNAME whose target is the wildcard top-level
domain (*.).
It rewrites the response to NODATA or ANCOUNT=1.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>Local Data</strong></span></span></dt>
<dd>
<p>
A set of ordinary DNS records can be used to answer queries.
Queries for record types not the set are answered with
NODATA.
</p>
<p>
A special form of local data is a CNAME whose target is a
wildcard such as *.example.com.
It is used as if were an ordinary CNAME after the asterisk (*)
has been replaced with the query name.
The purpose for this special form is query logging in the
walled garden's authority DNS server.
</p>
</dd>
</dl></div>
<p>
</p>
<p>
All of the actions specified in all of the individual records
in a policy zone
can be overridden with a <span class="command"><strong>policy</strong></span> clause in the
<span class="command"><strong>response-policy</strong></span> option.
An organization using a policy zone provided by another
organization might use this mechanism to redirect domains
to its own walled garden.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>GIVEN</strong></span></span></dt>
<dd>
<p>The placeholder policy says "do not override but
perform the action specified in the zone."
</p>
</dd>
<dt><span class="term"><span class="command"><strong>DISABLED</strong></span></span></dt>
<dd>
<p>
The testing override policy causes policy zone records to do
nothing but log what they would have done if the
policy zone were not disabled.
The response to the DNS query will be written (or not)
according to any triggered policy records that are not
disabled.
Disabled policy zones should appear first,
because they will often not be logged
if a higher precedence trigger is found first.
</p>
</dd>
<dt>
<span class="term"><span class="command"><strong>PASSTHRU</strong></span>, </span><span class="term"><span class="command"><strong>DROP</strong></span>, </span><span class="term"><span class="command"><strong>TCP-Only</strong></span>, </span><span class="term"><span class="command"><strong>NXDOMAIN</strong></span>, </span><span class="term"><span class="command"><strong>NODATA</strong></span></span>
</dt>
<dd>
<p>
override with the corresponding per-record policy.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>CNAME domain</strong></span></span></dt>
<dd>
<p>
causes all RPZ policy records to act as if they were
"cname domain" records.
</p>
</dd>
</dl></div>
<p>
</p>
<p>
By default, the actions encoded in a response policy zone
are applied only to queries that ask for recursion (RD=1).
That default can be changed for a single policy zone or
all response policy zones in a view
with a <span class="command"><strong>recursive-only no</strong></span> clause.
This feature is useful for serving the same zone files
both inside and outside an RFC 1918 cloud and using RPZ to
delete answers that would otherwise contain RFC 1918 values
on the externally visible name server or view.
</p>
<p>
Also by default, RPZ actions are applied only to DNS requests
that either do not request DNSSEC metadata (DO=0) or when no
DNSSEC records are available for request name in the original
zone (not the response policy zone). This default can be
changed for all response policy zones in a view with a
<span class="command"><strong>break-dnssec yes</strong></span> clause. In that case, RPZ
actions are applied regardless of DNSSEC. The name of the
clause option reflects the fact that results rewritten by RPZ
actions cannot verify.
</p>
<p>
No DNS records are needed for a QNAME or Client-IP trigger.
The name or IP address itself is sufficient,
so in principle the query name need not be recursively resolved.
However, not resolving the requested
name can leak the fact that response policy rewriting is in use
and that the name is listed in a policy zone to operators of
servers for listed names. To prevent that information leak, by
default any recursion needed for a request is done before any
policy triggers are considered. Because listed domains often
have slow authoritative servers, this default behavior can cost
significant time.
The <span class="command"><strong>qname-wait-recurse no</strong></span> 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 <span class="command"><strong>break-dnssec yes</strong></span>
is in use, because the response would depend on whether or not
RRSIG records were found during resolution.
Using this option can cause error responses such as SERVFAIL to
appear to be rewritten, since no recursion is being done to
discover problems at the authoritative server.
</p>
<p>
The TTL of a record modified by RPZ policies is set from the
TTL of the relevant record in policy zone. It is then limited
to a maximum value.
The <span class="command"><strong>max-policy-ttl</strong></span> clause changes the
maximum seconds from its default of 5.
</p>
<p>
For example, you might use this option statement
</p>
<pre class="programlisting"> response-policy { zone "badlist"; };</pre>
<p>
and this zone statement
</p>
<pre class="programlisting"> zone "badlist" {type master; file "master/badlist"; allow-query {none;}; };</pre>
<p>
with this zone file
</p>
<pre class="programlisting">$TTL 1H
@ SOA LOCALHOST. named-mgr.example.com (1 1h 15m 30d 2h)
NS LOCALHOST.
; QNAME policy records. There are no periods (.) after the owner names.
nxdomain.domain.com CNAME . ; NXDOMAIN policy
*.nxdomain.domain.com CNAME . ; NXDOMAIN policy
nodata.domain.com CNAME *. ; NODATA policy
*.nodata.domain.com CNAME *. ; NODATA policy
bad.domain.com A 10.0.0.1 ; redirect to a walled garden
AAAA 2001:2::1
bzone.domain.com CNAME garden.example.com.
; do not rewrite (PASSTHRU) OK.DOMAIN.COM
ok.domain.com CNAME rpz-passthru.
; redirect x.bzone.domain.com to x.bzone.domain.com.garden.example.com
*.bzone.domain.com CNAME *.garden.example.com.
; IP policy records that rewrite all responses containing A records in 127/8
; except 127.0.0.1
8.0.0.0.127.rpz-ip CNAME .
32.1.0.0.127.rpz-ip CNAME rpz-passthru.
; NSDNAME and NSIP policy records
ns.domain.com.rpz-nsdname CNAME .
48.zz.2.2001.rpz-nsip CNAME .
; blacklist and whitelist some DNS clients
112.zz.2001.rpz-client-ip CNAME rpz-drop.
8.0.0.0.127.rpz-client-ip CNAME rpz-drop.
; force some DNS clients and responses in the example.com zone to TCP
16.0.0.1.10.rpz-client-ip CNAME rpz-tcp-only.
example.com CNAME rpz-tcp-only.
*.example.com CNAME rpz-tcp-only.
</pre>
<p>
RPZ can affect server performance.
Each configured response policy zone requires the server to
perform one to four additional database lookups before a
query can be answered.
For example, a DNS server with four policy zones, each with all
four kinds of response triggers, QNAME, IP, NSIP, and
NSDNAME, requires a total of 17 times as many database
lookups as a similar DNS server with no response policy zones.
A <acronym class="acronym">BIND9</acronym> server with adequate memory and one
response policy zone with QNAME and IP triggers might achieve a
maximum queries-per-second rate about 20% lower.
A server with four response policy zones with QNAME and IP
triggers might have a maximum QPS rate about 50% lower.
</p>
<p>
Responses rewritten by RPZ are counted in the
<span class="command"><strong>RPZRewrites</strong></span> statistics.
</p>
<p>
The <span class="command"><strong>log</strong></span> clause can be used to optionally
turn off rewrite logging for a particular response policy
zone. By default, all rewrites are logged.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="rrl"></a>Response Rate Limiting</h4></div></div></div>
<p>
Excessive almost identical UDP <span class="emphasis"><em>responses</em></span>
can be controlled by configuring a
<span class="command"><strong>rate-limit</strong></span> clause in an
<span class="command"><strong>options</strong></span> or <span class="command"><strong>view</strong></span> statement.
This mechanism keeps authoritative BIND 9 from being used
in amplifying reflection denial of service (DoS) attacks.
Short truncated (TC=1) responses can be sent to provide
rate-limited responses to legitimate clients within
a range of forged, attacked IP addresses.
Legitimate clients react to dropped or truncated response
by retrying with UDP or with TCP respectively.
</p>
<p>
This mechanism is intended for authoritative DNS servers.
It can be used on recursive servers but can slow
applications such as SMTP servers (mail receivers) and
HTTP clients (web browsers) that repeatedly request the
same domains.
When possible, closing "open" recursive servers is better.
</p>
<p>
Response rate limiting uses a "credit" or "token bucket" scheme.
Each combination of identical response and client
has a conceptual account that earns a specified number
of credits every second.
A prospective response debits its account by one.
Responses are dropped or truncated
while the account is negative.
Responses are tracked within a rolling window of time
which defaults to 15 seconds, but can be configured with
the <span class="command"><strong>window</strong></span> option to any value from
1 to 3600 seconds (1 hour).
The account cannot become more positive than
the per-second limit
or more negative than <span class="command"><strong>window</strong></span>
times the per-second limit.
When the specified number of credits for a class of
responses is set to 0, those responses are not rate limited.
</p>
<p>
The notions of "identical response" and "DNS client"
for rate limiting are not simplistic.
All responses to an address block are counted as if to a
single client.
The prefix lengths of addresses blocks are
specified with <span class="command"><strong>ipv4-prefix-length</strong></span> (default 24)
and <span class="command"><strong>ipv6-prefix-length</strong></span> (default 56).
</p>
<p>
All non-empty responses for a valid domain name (qname)
and record type (qtype) are identical and have a limit specified
with <span class="command"><strong>responses-per-second</strong></span>
(default 0 or no limit).
All empty (NODATA) responses for a valid domain,
regardless of query type, are identical.
Responses in the NODATA class are limited by
<span class="command"><strong>nodata-per-second</strong></span>
(default <span class="command"><strong>responses-per-second</strong></span>).
Requests for any and all undefined subdomains of a given
valid domain result in NXDOMAIN errors, and are identical
regardless of query type.
They are limited by <span class="command"><strong>nxdomains-per-second</strong></span>
(default <span class="command"><strong>responses-per-second</strong></span>).
This controls some attacks using random names, but
can be relaxed or turned off (set to 0)
on servers that expect many legitimate
NXDOMAIN responses, such as from anti-spam blacklists.
Referrals or delegations to the server of a given
domain are identical and are limited by
<span class="command"><strong>referrals-per-second</strong></span>
(default <span class="command"><strong>responses-per-second</strong></span>).
</p>
<p>
Responses generated from local wildcards are counted and limited
as if they were for the parent domain name.
This controls flooding using random.wild.example.com.
</p>
<p>
All requests that result in DNS errors other
than NXDOMAIN, such as SERVFAIL and FORMERR, are identical
regardless of requested name (qname) or record type (qtype).
This controls attacks using invalid requests or distant,
broken authoritative servers.
By default the limit on errors is the same as the
<span class="command"><strong>responses-per-second</strong></span> value,
but it can be set separately with
<span class="command"><strong>errors-per-second</strong></span>.
</p>
<p>
Many attacks using DNS involve UDP requests with forged source
addresses.
Rate limiting prevents the use of BIND 9 to flood a network
with responses to requests with forged source addresses,
but could let a third party block responses to legitimate requests.
There is a mechanism that can answer some legitimate
requests from a client whose address is being forged in a flood.
Setting <span class="command"><strong>slip</strong></span> to 2 (its default) causes every
other UDP request to be answered with a small truncated (TC=1)
response.
The small size and reduced frequency, and so lack of
amplification, of "slipped" responses make them unattractive
for reflection DoS attacks.
<span class="command"><strong>slip</strong></span> must be between 0 and 10.
A value of 0 does not "slip":
no truncated responses are sent due to rate limiting,
all responses are dropped.
A value of 1 causes every response to slip;
values between 2 and 10 cause every n'th response to slip.
Some error responses including REFUSED and SERVFAIL
cannot be replaced with truncated responses and are instead
leaked at the <span class="command"><strong>slip</strong></span> rate.
</p>
<p>
(NOTE: Dropped responses from an authoritative server may
reduce the difficulty of a third party successfully forging
a response to a recursive resolver. The best security
against forged responses is for authoritative operators
to sign their zones using DNSSEC and for resolver operators
to validate the responses. When this is not an option,
operators who are more concerned with response integrity
than with flood mitigation may consider setting
<span class="command"><strong>slip</strong></span> to 1, causing all rate-limited
responses to be truncated rather than dropped. This reduces
the effectiveness of rate-limiting against reflection attacks.)
</p>
<p>
When the approximate query per second rate exceeds
the <span class="command"><strong>qps-scale</strong></span> value,
then the <span class="command"><strong>responses-per-second</strong></span>,
<span class="command"><strong>errors-per-second</strong></span>,
<span class="command"><strong>nxdomains-per-second</strong></span> and
<span class="command"><strong>all-per-second</strong></span> values are reduced by the
ratio of the current rate to the <span class="command"><strong>qps-scale</strong></span> value.
This feature can tighten defenses during attacks.
For example, with
<span class="command"><strong>qps-scale 250; responses-per-second 20;</strong></span> and
a total query rate of 1000 queries/second for all queries from
all DNS clients including via TCP,
then the effective responses/second limit changes to
(250/1000)*20 or 5.
Responses sent via TCP are not limited
but are counted to compute the query per second rate.
</p>
<p>
Rate limiters for different name spaces maintain
separate counters: If, for example, there is a
<span class="command"><strong>rate-limit</strong></span> statement for "com" and
another for "example.com", queries matching "example.com"
will not be debited against the rate limiter for "com".
</p>
<p>
If a <span class="command"><strong>rate-limit</strong></span> statement does not specify a
<span class="command"><strong>domain</strong></span>, then it applies to the root domain
(".") and thus affects the entire DNS namespace, except those
portions covered by other <span class="command"><strong>rate-limit</strong></span>
statements.
</p>
<p>
Communities of DNS clients can be given their own parameters or no
rate limiting by putting
<span class="command"><strong>rate-limit</strong></span> statements in <span class="command"><strong>view</strong></span>
statements instead of the global <span class="command"><strong>option</strong></span>
statement.
A <span class="command"><strong>rate-limit</strong></span> statement in a view replaces,
rather than supplementing, a <span class="command"><strong>rate-limit</strong></span>
statement among the main options.
DNS clients within a view can be exempted from rate limits
with the <span class="command"><strong>exempt-clients</strong></span> clause.
</p>
<p>
UDP responses of all kinds can be limited with the
<span class="command"><strong>all-per-second</strong></span> phrase. This rate
limiting is unlike the rate limiting provided by
<span class="command"><strong>responses-per-second</strong></span>,
<span class="command"><strong>errors-per-second</strong></span>, and
<span class="command"><strong>nxdomains-per-second</strong></span> on a DNS server
which are often invisible to the victim of a DNS
reflection attack. Unless the forged requests of the
attack are the same as the legitimate requests of the
victim, the victim's requests are not affected. Responses
affected by an <span class="command"><strong>all-per-second</strong></span> limit
are always dropped; the <span class="command"><strong>slip</strong></span> value
has no effect. An <span class="command"><strong>all-per-second</strong></span>
limit should be at least 4 times as large as the other
limits, because single DNS clients often send bursts
of legitimate requests. For example, the receipt of a
single mail message can prompt requests from an SMTP
server for NS, PTR, A, and AAAA records as the incoming
SMTP/TCP/IP connection is considered. The SMTP server
can need additional NS, A, AAAA, MX, TXT, and SPF records
as it considers the STMP <span class="command"><strong>Mail From</strong></span>
command. Web browsers often repeatedly resolve the
same names that are repeated in HTML <IMG> tags
in a page. <span class="command"><strong>all-per-second</strong></span> is similar
to the rate limiting offered by firewalls but often
inferior. Attacks that justify ignoring the contents
of DNS responses are likely to be attacks on the DNS
server itself. They usually should be discarded before
the DNS server spends resources make TCP connections
or parsing DNS requests, but that rate limiting must
be done before the DNS server sees the requests.
</p>
<p>
The maximum size of the table used to track requests and
rate limit responses is set with <span class="command"><strong>max-table-size</strong></span>.
Each entry in the table is between 40 and 80 bytes.
The table needs approximately as many entries as the number
of requests received per second.
The default is 20,000.
To reduce the cold start of growing the table,
<span class="command"><strong>min-table-size</strong></span> (default 500)
can set the minimum table size.
Enable <span class="command"><strong>rate-limit</strong></span> category logging to monitor
expansions of the table and inform
choices for the initial and maximum table size.
</p>
<p>
Use <span class="command"><strong>log-only yes</strong></span> to test rate limiting parameters
without actually dropping any requests.
</p>
<p>
Responses dropped by rate limits are included in the
<span class="command"><strong>RateDropped</strong></span> and <span class="command"><strong>QryDropped</strong></span>
statistics.
Responses that truncated by rate limits are included in
<span class="command"><strong>RateSlipped</strong></span> and <span class="command"><strong>RespTruncated</strong></span>.
</p>
</div>
<div class="section">
<div class="titlepage"></div>
<p>
Named supports NXDOMAIN redirection via two methods:
</p>
<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 “<span class="command"><strong>zone</strong></span>
Statement Grammar”</a>
</li>
<li class="listitem">Redirect namespace</li>
</ul></div>
<p>
</p>
<p>
With both methods when named gets a NXDOMAIN response
it examines a separate namespace to see if the NXDOMAIN
response should be replaced with an alternative response.
</p>
<p>
With a redirect zone (<span class="command"><strong>zone "." { type redirect; };</strong></span>), 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.
</p>
<p>
With a redirect namespace (<span class="command"><strong>option { nxdomain-redirect
<suffix> };</strong></span>) the data used to replace the
NXDOMAIN is part of the normal namespace and is looked up by
appending the specified suffix to the original query name.
This roughly doubles the cache required to process NXDOMAIN
responses as you have the original NXDOMAIN response and
the replacement data or a NXDOMAIN indicating that there
is no replacement.
</p>
<p>
If both a redirect zone and a redirect namespace are configured,
the redirect zone is tried first.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="server_statement_grammar"></a><span class="command"><strong>server</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting">
<span class="command"><strong>server</strong></span> <em class="replaceable"><code>netprefix</code></em> {
<span class="command"><strong>bogus</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>edns</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>edns-udp-size</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>edns-version</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>keys</strong></span> <em class="replaceable"><code>server_key</code></em>;
<span class="command"><strong>max-udp-size</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>notify-source</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [
<span class="command"><strong>dscp</strong></span> <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>notify-source-v6</strong></span> ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ]
[ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>provide-ixfr</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>query-source</strong></span> ( ( [ address ] ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port (
<em class="replaceable"><code>integer</code></em> | * ) ] ) | ( [ [ address ] ( <em class="replaceable"><code>ipv4_address</code></em> | * ) ]
<span class="command"><strong>port</strong></span> ( <em class="replaceable"><code>integer</code></em> | * ) ) ) [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>query-source-v6</strong></span> ( ( [ address ] ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port (
<em class="replaceable"><code>integer</code></em> | * ) ] ) | ( [ [ address ] ( <em class="replaceable"><code>ipv6_address</code></em> | * ) ]
<span class="command"><strong>port</strong></span> ( <em class="replaceable"><code>integer</code></em> | * ) ) ) [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>request-expire</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>request-ixfr</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>request-nsid</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>send-cookie</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>tcp-only</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>transfer-format</strong></span> ( many-answers | one-answer );
<span class="command"><strong>transfer-source</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [
<span class="command"><strong>dscp</strong></span> <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>transfer-source-v6</strong></span> ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * )
] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>transfers</strong></span> <em class="replaceable"><code>integer</code></em>;
};
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="server_statement_definition_and_usage"></a><span class="command"><strong>server</strong></span> Statement Definition and
Usage</h3></div></div></div>
<p>
The <span class="command"><strong>server</strong></span> statement defines
characteristics
to be associated with a remote name server. If a prefix length is
specified, then a range of servers is covered. Only the most
specific
server clause applies regardless of the order in
<code class="filename">named.conf</code>.
</p>
<p>
The <span class="command"><strong>server</strong></span> statement can occur at
the top level of the
configuration file or inside a <span class="command"><strong>view</strong></span>
statement.
If a <span class="command"><strong>view</strong></span> statement contains
one or more <span class="command"><strong>server</strong></span> statements, only
those
apply to the view and any top-level ones are ignored.
If a view contains no <span class="command"><strong>server</strong></span>
statements,
any top-level <span class="command"><strong>server</strong></span> statements are
used as
defaults.
</p>
<p>
If you discover that a remote server is giving out bad data,
marking it as bogus will prevent further queries to it. The
default
value of <span class="command"><strong>bogus</strong></span> is <span class="command"><strong>no</strong></span>.
</p>
<p>
The <span class="command"><strong>provide-ixfr</strong></span> clause determines
whether
the local server, acting as master, will respond with an
incremental
zone transfer when the given remote server, a slave, requests it.
If set to <span class="command"><strong>yes</strong></span>, incremental transfer
will be provided
whenever possible. If set to <span class="command"><strong>no</strong></span>,
all transfers
to the remote server will be non-incremental. If not set, the
value
of the <span class="command"><strong>provide-ixfr</strong></span> option in the
view or
global options block is used as a default.
</p>
<p>
The <span class="command"><strong>request-ixfr</strong></span> clause determines
whether
the local server, acting as a slave, will request incremental zone
transfers from the given remote server, a master. If not set, the
value of the <span class="command"><strong>request-ixfr</strong></span> option in
the view or global options block is used as a default. It may
also be set in the zone block and, if set there, it will
override the global or view setting for that zone.
</p>
<p>
IXFR requests to servers that do not support IXFR will
automatically
fall back to AXFR. Therefore, there is no need to manually list
which servers support IXFR and which ones do not; the global
default
of <span class="command"><strong>yes</strong></span> should always work.
The purpose of the <span class="command"><strong>provide-ixfr</strong></span> and
<span class="command"><strong>request-ixfr</strong></span> clauses is
to make it possible to disable the use of IXFR even when both
master
and slave claim to support it, for example if one of the servers
is buggy and crashes or corrupts data when IXFR is used.
</p>
<p>
The <span class="command"><strong>request-expire</strong></span> clause determines
whether the local server, when acting as a slave, will
request the EDNS EXPIRE value. The EDNS EXPIRE value
indicates the remaining time before the zone data will
expire and need to be be refreshed. This is used
when a secondary server transfers a zone from another
secondary server; when transferring from the primary, the
expiration timer is set from the EXPIRE field of the SOA
record instead.
The default is <span class="command"><strong>yes</strong></span>.
</p>
<p>
The <span class="command"><strong>edns</strong></span> clause determines whether
the local server will attempt to use EDNS when communicating
with the remote server. The default is <span class="command"><strong>yes</strong></span>.
</p>
<p>
The <span class="command"><strong>edns-udp-size</strong></span> option sets the
EDNS UDP size that is advertised by <span class="command"><strong>named</strong></span>
when querying the remote server. Valid values are 512
to 4096 bytes (values outside this range will be silently
adjusted to the nearest value within it). This option
is useful when you wish to advertise a different value
to this server than the value you advertise globally,
for example, when there is a firewall at the remote
site that is blocking large replies. (Note: Currently,
this sets a single UDP size for all packets sent to the
server; <span class="command"><strong>named</strong></span> will not deviate from
this value. This differs from the behavior of
<span class="command"><strong>edns-udp-size</strong></span> in <span class="command"><strong>options</strong></span>
or <span class="command"><strong>view</strong></span> statements, where it specifies
a maximum value. The <span class="command"><strong>server</strong></span> statement
behavior may be brought into conformance with the
<span class="command"><strong>options/view</strong></span> behavior in future releases.)
</p>
<p>
The <span class="command"><strong>edns-version</strong></span> option sets the
maximum EDNS VERSION that will be sent to the server(s)
by the resolver. The actual EDNS version sent is still
subject to normal EDNS version negotiation rules (see
RFC 6891), the maximum EDNS version supported by the
server, and any other heuristics that indicate that a
lower version should be sent. This option is intended
to be used when a remote server reacts badly to a given
EDNS version or higher; it should be set to the highest
version the remote server is known to support. Valid
values are 0 to 255; higher values will be silently
adjusted. This option will not be needed until higher
EDNS versions than 0 are in use.
</p>
<p>
The <span class="command"><strong>max-udp-size</strong></span> option sets the
maximum EDNS UDP message size <span class="command"><strong>named</strong></span>
will send. Valid values are 512 to 4096 bytes (values
outside this range will be silently adjusted). This
option is useful when you know that there is a firewall
that is blocking large replies from <span class="command"><strong>named</strong></span>.
</p>
<p>
The <span class="command"><strong>tcp-only</strong></span> 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.
</p>
<p>
The server supports two zone transfer methods. The first, <span class="command"><strong>one-answer</strong></span>,
uses one DNS message per resource record transferred. <span class="command"><strong>many-answers</strong></span> packs
as many resource records as possible into a message. <span class="command"><strong>many-answers</strong></span> is
more efficient, but is only known to be understood by <acronym class="acronym">BIND</acronym> 9, <acronym class="acronym">BIND</acronym>
8.x, and patched versions of <acronym class="acronym">BIND</acronym>
4.9.5. You can specify which method
to use for a server with the <span class="command"><strong>transfer-format</strong></span> option.
If <span class="command"><strong>transfer-format</strong></span> is not
specified, the <span class="command"><strong>transfer-format</strong></span>
specified
by the <span class="command"><strong>options</strong></span> statement will be
used.
</p>
<p><span class="command"><strong>transfers</strong></span>
is used to limit the number of concurrent inbound zone
transfers from the specified server. If no
<span class="command"><strong>transfers</strong></span> clause is specified, the
limit is set according to the
<span class="command"><strong>transfers-per-ns</strong></span> option.
</p>
<p>
The <span class="command"><strong>keys</strong></span> clause identifies a
<span class="command"><strong>key_id</strong></span> defined by the <span class="command"><strong>key</strong></span> statement,
to be used for transaction security (TSIG, <a class="xref" href="Bv9ARM.ch04.html#tsig" title="TSIG">the section called “TSIG”</a>)
when talking to the remote server.
When a request is sent to the remote server, a request signature
will be generated using the key specified here and appended to the
message. A request originating from the remote server is not
required
to be signed by this key.
</p>
<p>
Only a single key per server is currently supported.
</p>
<p>
The <span class="command"><strong>transfer-source</strong></span> and
<span class="command"><strong>transfer-source-v6</strong></span> clauses specify
the IPv4 and IPv6 source
address to be used for zone transfer with the remote server,
respectively.
For an IPv4 remote server, only <span class="command"><strong>transfer-source</strong></span> can
be specified.
Similarly, for an IPv6 remote server, only
<span class="command"><strong>transfer-source-v6</strong></span> can be
specified.
For more details, see the description of
<span class="command"><strong>transfer-source</strong></span> and
<span class="command"><strong>transfer-source-v6</strong></span> in
<a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
<p>
The <span class="command"><strong>notify-source</strong></span> and
<span class="command"><strong>notify-source-v6</strong></span> clauses specify the
IPv4 and IPv6 source address to be used for notify
messages sent to remote servers, respectively. For an
IPv4 remote server, only <span class="command"><strong>notify-source</strong></span>
can be specified. Similarly, for an IPv6 remote server,
only <span class="command"><strong>notify-source-v6</strong></span> can be specified.
</p>
<p>
The <span class="command"><strong>query-source</strong></span> and
<span class="command"><strong>query-source-v6</strong></span> clauses specify the
IPv4 and IPv6 source address to be used for queries
sent to remote servers, respectively. For an IPv4
remote server, only <span class="command"><strong>query-source</strong></span> can
be specified. Similarly, for an IPv6 remote server,
only <span class="command"><strong>query-source-v6</strong></span> can be specified.
</p>
<p>
The <span class="command"><strong>request-nsid</strong></span> clause determines
whether the local server will add a NSID EDNS option
to requests sent to the server. This overrides
<span class="command"><strong>request-nsid</strong></span> set at the view or
option level.
</p>
<p>
The <span class="command"><strong>send-cookie</strong></span> clause determines
whether the local server will add a COOKIE EDNS option
to requests sent to the server. This overrides
<span class="command"><strong>send-cookie</strong></span> set at the view or
option level. The <span class="command"><strong>named</strong></span> server may
determine that COOKIE is not supported by the remote server
and not add a COOKIE EDNS option to requests.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="statschannels"></a><span class="command"><strong>statistics-channels</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting">
<span class="command"><strong>statistics-channels</strong></span> {
<span class="command"><strong>inet</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | <em class="replaceable"><code>ipv6_address</code></em> |
* ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [
<span class="command"><strong>allow</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ...
} ];
};
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="statistics_channels"></a><span class="command"><strong>statistics-channels</strong></span> Statement Definition and
Usage</h3></div></div></div>
<p>
The <span class="command"><strong>statistics-channels</strong></span> statement
declares communication channels to be used by system
administrators to get access to statistics information of
the name server.
</p>
<p>
This statement intends to be flexible to support multiple
communication protocols in the future, but currently only
HTTP access is supported.
It requires that BIND 9 be compiled with libxml2 and/or
json-c (also known as libjson0); the
<span class="command"><strong>statistics-channels</strong></span> statement is
still accepted even if it is built without the library,
but any HTTP access will fail with an error.
</p>
<p>
An <span class="command"><strong>inet</strong></span> control channel is a TCP socket
listening at the specified <span class="command"><strong>ip_port</strong></span> on the
specified <span class="command"><strong>ip_addr</strong></span>, which can be an IPv4 or IPv6
address. An <span class="command"><strong>ip_addr</strong></span> of <code class="literal">*</code>
(asterisk) is
interpreted as the IPv4 wildcard address; connections will be
accepted on any of the system's IPv4 addresses.
To listen on the IPv6 wildcard address,
use an <span class="command"><strong>ip_addr</strong></span> of <code class="literal">::</code>.
</p>
<p>
If no port is specified, port 80 is used for HTTP channels.
The asterisk "<code class="literal">*</code>" cannot be used for
<span class="command"><strong>ip_port</strong></span>.
</p>
<p>
The attempt of opening a statistics channel is
restricted by the optional <span class="command"><strong>allow</strong></span> clause.
Connections to the statistics channel are permitted based on the
<span class="command"><strong>address_match_list</strong></span>.
If no <span class="command"><strong>allow</strong></span> clause is present,
<span class="command"><strong>named</strong></span> accepts connection
attempts from any address; since the statistics may
contain sensitive internal information, it is highly
recommended to restrict the source of connection requests
appropriately.
</p>
<p>
If no <span class="command"><strong>statistics-channels</strong></span> statement is present,
<span class="command"><strong>named</strong></span> will not open any communication channels.
</p>
<p>
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.
</p>
<p>
Applications that depend on a particular XML schema
can request
<a class="link" href="http://127.0.0.1:8888/xml/v2" target="_top">http://127.0.0.1:8888/xml/v2</a> for version 2
of the statistics XML schema or
<a class="link" href="http://127.0.0.1:8888/xml/v3" target="_top">http://127.0.0.1:8888/xml/v3</a> for version 3.
If the requested schema is supported by the server, then
it will respond; if not, it will return a "page not found"
error.
</p>
<p>
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).
</p>
<p>
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).
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="trusted-keys"></a><span class="command"><strong>trusted-keys</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting">
<span class="command"><strong>trusted-keys</strong></span> { <em class="replaceable"><code>string</code></em> <em class="replaceable"><code>integer</code></em> <em class="replaceable"><code>integer</code></em>
<em class="replaceable"><code>integer</code></em> <em class="replaceable"><code>quoted_string</code></em>; ... };
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="trusted_keys"></a><span class="command"><strong>trusted-keys</strong></span> Statement Definition
and Usage</h3></div></div></div>
<p>
The <span class="command"><strong>trusted-keys</strong></span> statement defines
DNSSEC security roots. DNSSEC is described in <a class="xref" href="Bv9ARM.ch04.html#DNSSEC" title="DNSSEC">the section called “DNSSEC”</a>. A security root is defined when the
public key for a non-authoritative zone is known, but
cannot be securely obtained through DNS, either because
it is the DNS root zone or because its parent zone is
unsigned. Once a key has been configured as a trusted
key, it is treated as if it had been validated and
proven secure. The resolver attempts DNSSEC validation
on all DNS data in subdomains of a security root.
</p>
<p>
All keys (and corresponding zones) listed in
<span class="command"><strong>trusted-keys</strong></span> are deemed to exist regardless
of what parent zones say. Similarly for all keys listed in
<span class="command"><strong>trusted-keys</strong></span> only those keys are
used to validate the DNSKEY RRset. The parent's DS RRset
will not be used.
</p>
<p>
The <span class="command"><strong>trusted-keys</strong></span> statement can contain
multiple key entries, each consisting of the key's
domain name, flags, protocol, algorithm, and the Base64
representation of the key data.
Spaces, tabs, newlines and carriage returns are ignored
in the key data, so the configuration may be split up into
multiple lines.
</p>
<p>
<span class="command"><strong>trusted-keys</strong></span> may be set at the top level
of <code class="filename">named.conf</code> or within a view. If it is
set in both places, they are additive: keys defined at the top
level are inherited by all views, but keys defined in a view
are only used within that view.
</p>
<p>
Validation below specified names can be temporarily disabled
by using <span class="command"><strong>rndc nta</strong></span>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="managed_keys"></a><span class="command"><strong>managed-keys</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting">
<span class="command"><strong>managed-keys</strong></span> { <em class="replaceable"><code>string</code></em> <em class="replaceable"><code>string</code></em> <em class="replaceable"><code>integer</code></em>
<em class="replaceable"><code>integer</code></em> <em class="replaceable"><code>integer</code></em> <em class="replaceable"><code>quoted_string</code></em>; ... };
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="managed-keys"></a><span class="command"><strong>managed-keys</strong></span> Statement Definition
and Usage</h3></div></div></div>
<p>
The <span class="command"><strong>managed-keys</strong></span> statement, like
<span class="command"><strong>trusted-keys</strong></span>, defines DNSSEC
security roots. The difference is that
<span class="command"><strong>managed-keys</strong></span> can be kept up to date
automatically, without intervention from the resolver
operator.
</p>
<p>
Suppose, for example, that a zone's key-signing
key was compromised, and the zone owner had to revoke and
replace the key. A resolver which had the old key in a
<span class="command"><strong>trusted-keys</strong></span> statement would be
unable to validate this zone any longer; it would
reply with a SERVFAIL response code. This would
continue until the resolver operator had updated the
<span class="command"><strong>trusted-keys</strong></span> statement with the new key.
</p>
<p>
If, however, the zone were listed in a
<span class="command"><strong>managed-keys</strong></span> statement instead, then the
zone owner could add a "stand-by" key to the zone in advance.
<span class="command"><strong>named</strong></span> would store the stand-by key, and
when the original key was revoked, <span class="command"><strong>named</strong></span>
would be able to transition smoothly to the new key. It would
also recognize that the old key had been revoked, and cease
using that key to validate answers, minimizing the damage that
the compromised key could do.
</p>
<p>
A <span class="command"><strong>managed-keys</strong></span> statement contains a list of
the keys to be managed, along with information about how the
keys are to be initialized for the first time. The only
initialization method currently supported is
<code class="literal">initial-key</code>.
This means the <span class="command"><strong>managed-keys</strong></span> statement must
contain a copy of the initializing key. (Future releases may
allow keys to be initialized by other methods, eliminating this
requirement.)
</p>
<p>
Consequently, a <span class="command"><strong>managed-keys</strong></span> statement
appears similar to a <span class="command"><strong>trusted-keys</strong></span>, differing
in the presence of the second field, containing the keyword
<code class="literal">initial-key</code>. The difference is, whereas the
keys listed in a <span class="command"><strong>trusted-keys</strong></span> continue to be
trusted until they are removed from
<code class="filename">named.conf</code>, an initializing key listed
in a <span class="command"><strong>managed-keys</strong></span> statement is only trusted
<span class="emphasis"><em>once</em></span>: for as long as it takes to load the
managed key database and start the RFC 5011 key maintenance
process.
</p>
<p>
The first time <span class="command"><strong>named</strong></span> runs with a managed key
configured in <code class="filename">named.conf</code>, it fetches the
DNSKEY RRset directly from the zone apex, and validates it
using the key specified in the <span class="command"><strong>managed-keys</strong></span>
statement. If the DNSKEY RRset is validly signed, then it is
used as the basis for a new managed keys database.
</p>
<p>
From that point on, whenever <span class="command"><strong>named</strong></span> runs, it
sees the <span class="command"><strong>managed-keys</strong></span> statement, checks to
make sure RFC 5011 key maintenance has already been initialized
for the specified domain, and if so, it simply moves on. The
key specified in the <span class="command"><strong>managed-keys</strong></span>
statement is not used to validate answers; it has been
superseded by the key or keys stored in the managed keys database.
</p>
<p>
The next time <span class="command"><strong>named</strong></span> runs after a name
has been <span class="emphasis"><em>removed</em></span> from the
<span class="command"><strong>managed-keys</strong></span> statement, the corresponding
zone will be removed from the managed keys database,
and RFC 5011 key maintenance will no longer be used for that
domain.
</p>
<p>
In the current implementation, the managed keys database
is stored as a master-format zone file.
</p>
<p>
On servers which do not use views, this file is named
<code class="filename">managed-keys.bind</code>. When views are in
use, there will be a separate managed keys database for each
view; the filename will be the view name (or, if a view name
contains characters which would make it illegal as a filename,
a hash of the view name), followed by
the suffix <code class="filename">.mkeys</code>.
</p>
<p>
When the key database is changed, the zone is updated.
As with any other dynamic zone, changes will be written
into a journal file, e.g.,
<code class="filename">managed-keys.bind.jnl</code> or
<code class="filename">internal.mkeys.jnl</code>.
Changes are committed to the master file as soon as
possible afterward; this will usually occur within 30
seconds. So, whenever <span class="command"><strong>named</strong></span> 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 <span class="command"><strong>named</strong></span>.)
</p>
<p>
If the <span class="command"><strong>dnssec-validation</strong></span> option is
set to <strong class="userinput"><code>auto</code></strong>, <span class="command"><strong>named</strong></span>
will automatically initialize a managed key for the
root zone. The key that is used to initialize the key
maintenance process is stored in <code class="filename">bind.keys</code>;
the location of this file can be overridden with the
<span class="command"><strong>bindkeys-file</strong></span> 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 <span class="command"><strong>named</strong></span>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="view_statement_grammar"></a><span class="command"><strong>view</strong></span> Statement Grammar</h3></div></div></div>
<pre class="programlisting"><span class="command"><strong>view</strong></span> <em class="replaceable"><code>view_name</code></em> [ <em class="replaceable"><code>class</code></em> ] <span class="command"><strong>{</strong></span>
<span class="command"><strong>match-clients {</strong></span> <em class="replaceable"><code>address_match_list</code></em> <span class="command"><strong>}</strong></span> ;
<span class="command"><strong>match-destinations {</strong></span> <em class="replaceable"><code>address_match_list</code></em> <span class="command"><strong>}</strong></span> ;
<span class="command"><strong>match-recursive-only</strong></span> <em class="replaceable"><code>yes_or_no</code></em> ;
[ <em class="replaceable"><code>view_option</code></em> ; ... ]
[ <em class="replaceable"><code>zone_statement</code></em> ; ... ]
<span class="command"><strong>} </strong></span>;
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="view_statement"></a><span class="command"><strong>view</strong></span> Statement Definition and Usage</h3></div></div></div>
<p>
The <span class="command"><strong>view</strong></span> statement is a powerful
feature
of <acronym class="acronym">BIND</acronym> 9 that lets a name server
answer a DNS query differently
depending on who is asking. It is particularly useful for
implementing
split DNS setups without having to run multiple servers.
</p>
<p>
Each <span class="command"><strong>view</strong></span> statement defines a view
of the
DNS namespace that will be seen by a subset of clients. A client
matches
a view if its source IP address matches the
<code class="varname">address_match_list</code> of the view's
<span class="command"><strong>match-clients</strong></span> clause and its
destination IP address matches
the <code class="varname">address_match_list</code> of the
view's
<span class="command"><strong>match-destinations</strong></span> clause. If not
specified, both
<span class="command"><strong>match-clients</strong></span> and <span class="command"><strong>match-destinations</strong></span>
default to matching all addresses. In addition to checking IP
addresses
<span class="command"><strong>match-clients</strong></span> and <span class="command"><strong>match-destinations</strong></span>
can also take <span class="command"><strong>keys</strong></span> which provide an
mechanism for the
client to select the view. A view can also be specified
as <span class="command"><strong>match-recursive-only</strong></span>, which
means that only recursive
requests from matching clients will match that view.
The order of the <span class="command"><strong>view</strong></span> statements is
significant —
a client request will be resolved in the context of the first
<span class="command"><strong>view</strong></span> that it matches.
</p>
<p>
Zones defined within a <span class="command"><strong>view</strong></span>
statement will
only be accessible to clients that match the <span class="command"><strong>view</strong></span>.
By defining a zone of the same name in multiple views, different
zone data can be given to different clients, for example,
"internal"
and "external" clients in a split DNS setup.
</p>
<p>
Many of the options given in the <span class="command"><strong>options</strong></span> statement
can also be used within a <span class="command"><strong>view</strong></span>
statement, and then
apply only when resolving queries with that view. When no
view-specific
value is given, the value in the <span class="command"><strong>options</strong></span> statement
is used as a default. Also, zone options can have default values
specified
in the <span class="command"><strong>view</strong></span> statement; these
view-specific defaults
take precedence over those in the <span class="command"><strong>options</strong></span> statement.
</p>
<p>
Views are class specific. If no class is given, class IN
is assumed. Note that all non-IN views must contain a hint zone,
since only the IN class has compiled-in default hints.
</p>
<p>
If there are no <span class="command"><strong>view</strong></span> statements in
the config
file, a default view that matches any client is automatically
created
in class IN. Any <span class="command"><strong>zone</strong></span> statements
specified on
the top level of the configuration file are considered to be part
of
this default view, and the <span class="command"><strong>options</strong></span>
statement will
apply to the default view. If any explicit <span class="command"><strong>view</strong></span>
statements are present, all <span class="command"><strong>zone</strong></span>
statements must
occur inside <span class="command"><strong>view</strong></span> statements.
</p>
<p>
Here is an example of a typical split DNS setup implemented
using <span class="command"><strong>view</strong></span> statements:
</p>
<pre class="programlisting">view "internal" {
// This should match our internal networks.
match-clients { 10.0.0.0/8; };
// Provide recursive service to internal
// clients only.
recursion yes;
// Provide a complete view of the example.com
// zone including addresses of internal hosts.
zone "example.com" {
type master;
file "example-internal.db";
};
};
view "external" {
// Match all clients not matched by the
// previous view.
match-clients { any; };
// Refuse recursive service to external clients.
recursion no;
// Provide a restricted view of the example.com
// zone containing only publicly accessible hosts.
zone "example.com" {
type master;
file "example-external.db";
};
};
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="zone_statement_grammar"></a><span class="command"><strong>zone</strong></span>
Statement Grammar</h3></div></div></div>
<pre class="programlisting">
<span class="command"><strong>zone</strong></span> <em class="replaceable"><code>string</code></em> [ <em class="replaceable"><code>class</code></em> ] {
<span class="command"><strong>type</strong></span> ( master | primary );
<span class="command"><strong>allow-query</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-query-on</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-transfer</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-update</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>also-notify</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>masters</code></em> | <em class="replaceable"><code>ipv4_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] | <em class="replaceable"><code>ipv6_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] ) [ key <em class="replaceable"><code>string</code></em> ]; ... };
<span class="command"><strong>alt-transfer-source</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>alt-transfer-source-v6</strong></span> ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>auto-dnssec</strong></span> ( allow | maintain | off );
<span class="command"><strong>check-dup-records</strong></span> ( fail | warn | ignore );
<span class="command"><strong>check-integrity</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>check-mx</strong></span> ( fail | warn | ignore );
<span class="command"><strong>check-mx-cname</strong></span> ( fail | warn | ignore );
<span class="command"><strong>check-names</strong></span> ( fail | warn | ignore );
<span class="command"><strong>check-sibling</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>check-spf</strong></span> ( warn | ignore );
<span class="command"><strong>check-srv-cname</strong></span> ( fail | warn | ignore );
<span class="command"><strong>check-wildcard</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>database</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>dialup</strong></span> ( notify | notify-passive | passive | refresh | <em class="replaceable"><code>boolean</code></em> );
<span class="command"><strong>dlz</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>dnssec-dnskey-kskonly</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>dnssec-loadkeys-interval</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>dnssec-secure-to-insecure</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>dnssec-update-mode</strong></span> ( maintain | no-resign );
<span class="command"><strong>file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>forward</strong></span> ( first | only );
<span class="command"><strong>forwarders</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>ipv4_address</code></em> | <em class="replaceable"><code>ipv6_address</code></em> ) [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ]; ... };
<span class="command"><strong>inline-signing</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>ixfr-from-differences</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>journal</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>key-directory</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>masterfile-format</strong></span> ( map | raw | text );
<span class="command"><strong>masterfile-style</strong></span> ( full | relative );
<span class="command"><strong>max-journal-size</strong></span> ( unlimited | <em class="replaceable"><code>sizeval</code></em> );
<span class="command"><strong>max-records</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-idle-out</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-time-out</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-zone-ttl</strong></span> ( unlimited | <em class="replaceable"><code>ttlval</code></em> );
<span class="command"><strong>notify</strong></span> ( explicit | master-only | <em class="replaceable"><code>boolean</code></em> );
<span class="command"><strong>notify-delay</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>notify-source</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>notify-source-v6</strong></span> ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>notify-to-soa</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>serial-update-method</strong></span> ( date | increment | unixtime );
<span class="command"><strong>sig-signing-nodes</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>sig-signing-signatures</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>sig-signing-type</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>sig-validity-interval</strong></span> <em class="replaceable"><code>integer</code></em> [ <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>update-check-ksk</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>update-policy</strong></span> ( local | { ( deny | grant ) <em class="replaceable"><code>string</code></em> ( 6to4-self | external | krb5-self | krb5-selfsub | krb5-subdomain | ms-self | ms-selfsub | ms-subdomain | name | self | selfsub | selfwild | subdomain | tcp-self | wildcard | zonesub ) [ <em class="replaceable"><code>string</code></em> ] <em class="replaceable"><code>rrtypelist</code></em>; ... };
<span class="command"><strong>zero-no-soa-ttl</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>zone-statistics</strong></span> ( full | terse | none | <em class="replaceable"><code>boolean</code></em> );
};
</pre>
<pre class="programlisting">
<span class="command"><strong>zone</strong></span> <em class="replaceable"><code>string</code></em> [ <em class="replaceable"><code>class</code></em> ] {
<span class="command"><strong>type</strong></span> ( slave | secondary );
<span class="command"><strong>allow-notify</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-query</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-query-on</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-transfer</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-update-forwarding</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>also-notify</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>masters</code></em> | <em class="replaceable"><code>ipv4_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] | <em class="replaceable"><code>ipv6_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] ) [ key <em class="replaceable"><code>string</code></em> ]; ... };
<span class="command"><strong>alt-transfer-source</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>alt-transfer-source-v6</strong></span> ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>auto-dnssec</strong></span> ( allow | maintain | off );
<span class="command"><strong>check-names</strong></span> ( fail | warn | ignore );
<span class="command"><strong>database</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>dialup</strong></span> ( notify | notify-passive | passive | refresh | <em class="replaceable"><code>boolean</code></em> );
<span class="command"><strong>dlz</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>dnssec-dnskey-kskonly</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>dnssec-loadkeys-interval</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>dnssec-update-mode</strong></span> ( maintain | no-resign );
<span class="command"><strong>file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>forward</strong></span> ( first | only );
<span class="command"><strong>forwarders</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>ipv4_address</code></em> | <em class="replaceable"><code>ipv6_address</code></em> ) [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ]; ... };
<span class="command"><strong>inline-signing</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>ixfr-from-differences</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>journal</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>key-directory</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>masterfile-format</strong></span> ( map | raw | text );
<span class="command"><strong>masterfile-style</strong></span> ( full | relative );
<span class="command"><strong>masters</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>masters</code></em> | <em class="replaceable"><code>ipv4_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] | <em class="replaceable"><code>ipv6_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] ) [ key <em class="replaceable"><code>string</code></em> ]; ... };
<span class="command"><strong>max-journal-size</strong></span> ( unlimited | <em class="replaceable"><code>sizeval</code></em> );
<span class="command"><strong>max-records</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-refresh-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-retry-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-idle-in</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-idle-out</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-time-in</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-time-out</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>min-refresh-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>min-retry-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>multi-master</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>notify</strong></span> ( explicit | master-only | <em class="replaceable"><code>boolean</code></em> );
<span class="command"><strong>notify-delay</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>notify-source</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>notify-source-v6</strong></span> ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>notify-to-soa</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>request-expire</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>request-ixfr</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>sig-signing-nodes</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>sig-signing-signatures</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>sig-signing-type</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>sig-validity-interval</strong></span> <em class="replaceable"><code>integer</code></em> [ <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>transfer-source</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>transfer-source-v6</strong></span> ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>try-tcp-refresh</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>update-check-ksk</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>use-alt-transfer-source</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>zero-no-soa-ttl</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>zone-statistics</strong></span> ( full | terse | none | <em class="replaceable"><code>boolean</code></em> );
};
</pre>
<pre class="programlisting">
<span class="command"><strong>zone</strong></span> <em class="replaceable"><code>string</code></em> [ <em class="replaceable"><code>class</code></em> ] {
<span class="command"><strong>type</strong></span> hint;
<span class="command"><strong>check-names</strong></span> ( fail | warn | ignore );
<span class="command"><strong>delegation-only</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
};
</pre>
<pre class="programlisting">
<span class="command"><strong>zone</strong></span> <em class="replaceable"><code>string</code></em> [ <em class="replaceable"><code>class</code></em> ] {
<span class="command"><strong>type</strong></span> stub;
<span class="command"><strong>allow-query</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-query-on</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>check-names</strong></span> ( fail | warn | ignore );
<span class="command"><strong>database</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>delegation-only</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>dialup</strong></span> ( notify | notify-passive | passive | refresh | <em class="replaceable"><code>boolean</code></em> );
<span class="command"><strong>file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>forward</strong></span> ( first | only );
<span class="command"><strong>forwarders</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>ipv4_address</code></em> | <em class="replaceable"><code>ipv6_address</code></em> ) [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ]; ... };
<span class="command"><strong>masterfile-format</strong></span> ( map | raw | text );
<span class="command"><strong>masterfile-style</strong></span> ( full | relative );
<span class="command"><strong>masters</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>masters</code></em> | <em class="replaceable"><code>ipv4_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] | <em class="replaceable"><code>ipv6_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] ) [ key <em class="replaceable"><code>string</code></em> ]; ... };
<span class="command"><strong>max-records</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-refresh-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-retry-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-idle-in</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-transfer-time-in</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>min-refresh-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>min-retry-time</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>multi-master</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>transfer-source</strong></span> ( <em class="replaceable"><code>ipv4_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>transfer-source-v6</strong></span> ( <em class="replaceable"><code>ipv6_address</code></em> | * ) [ port ( <em class="replaceable"><code>integer</code></em> | * ) ] [ dscp <em class="replaceable"><code>integer</code></em> ];
<span class="command"><strong>use-alt-transfer-source</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>zone-statistics</strong></span> ( full | terse | none | <em class="replaceable"><code>boolean</code></em> );
};
</pre>
<pre class="programlisting">
<span class="command"><strong>zone</strong></span> <em class="replaceable"><code>string</code></em> [ <em class="replaceable"><code>class</code></em> ] {
<span class="command"><strong>type</strong></span> static-stub;
<span class="command"><strong>allow-query</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-query-on</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>forward</strong></span> ( first | only );
<span class="command"><strong>forwarders</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>ipv4_address</code></em> | <em class="replaceable"><code>ipv6_address</code></em> ) [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ]; ... };
<span class="command"><strong>max-records</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>server-addresses</strong></span> { ( <em class="replaceable"><code>ipv4_address</code></em> | <em class="replaceable"><code>ipv6_address</code></em> ) [ port <em class="replaceable"><code>integer</code></em> ]; ... };
<span class="command"><strong>server-names</strong></span> { <em class="replaceable"><code>quoted_string</code></em>; ... };
<span class="command"><strong>zone-statistics</strong></span> ( full | terse | none | <em class="replaceable"><code>boolean</code></em> );
};
</pre>
<pre class="programlisting">
<span class="command"><strong>zone</strong></span> <em class="replaceable"><code>string</code></em> [ <em class="replaceable"><code>class</code></em> ] {
<span class="command"><strong>type</strong></span> forward;
<span class="command"><strong>delegation-only</strong></span> <em class="replaceable"><code>boolean</code></em>;
<span class="command"><strong>forward</strong></span> ( first | only );
<span class="command"><strong>forwarders</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>ipv4_address</code></em> | <em class="replaceable"><code>ipv6_address</code></em> ) [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ]; ... };
};
</pre>
<pre class="programlisting">
<span class="command"><strong>zone</strong></span> <em class="replaceable"><code>string</code></em> [ <em class="replaceable"><code>class</code></em> ] {
<span class="command"><strong>type</strong></span> redirect;
<span class="command"><strong>allow-query</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>allow-query-on</strong></span> { <em class="replaceable"><code>address_match_element</code></em>; ... };
<span class="command"><strong>dlz</strong></span> <em class="replaceable"><code>string</code></em>;
<span class="command"><strong>file</strong></span> <em class="replaceable"><code>quoted_string</code></em>;
<span class="command"><strong>masterfile-format</strong></span> ( map | raw | text );
<span class="command"><strong>masterfile-style</strong></span> ( full | relative );
<span class="command"><strong>masters</strong></span> [ port <em class="replaceable"><code>integer</code></em> ] [ dscp <em class="replaceable"><code>integer</code></em> ] { ( <em class="replaceable"><code>masters</code></em> | <em class="replaceable"><code>ipv4_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] | <em class="replaceable"><code>ipv6_address</code></em> [ port <em class="replaceable"><code>integer</code></em> ] ) [ key <em class="replaceable"><code>string</code></em> ]; ... };
<span class="command"><strong>max-records</strong></span> <em class="replaceable"><code>integer</code></em>;
<span class="command"><strong>max-zone-ttl</strong></span> ( unlimited | <em class="replaceable"><code>ttlval</code></em> );
<span class="command"><strong>zone-statistics</strong></span> ( full | terse | none | <em class="replaceable"><code>boolean</code></em> );
};
</pre>
<pre class="programlisting">
<span class="command"><strong>zone</strong></span> <em class="replaceable"><code>string</code></em> [ <em class="replaceable"><code>class</code></em> ] {
<span class="command"><strong>type</strong></span> delegation-only;
};
</pre>
<pre class="programlisting">
<span class="command"><strong>zone</strong></span> <em class="replaceable"><code>string</code></em> [ <em class="replaceable"><code>class</code></em> ] {
<span class="command"><strong>in-view</strong></span> <em class="replaceable"><code>string</code></em>;
};
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="zone_statement"></a><span class="command"><strong>zone</strong></span> 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>
<p>
The <span class="command"><strong>type</strong></span> keyword is required
for the <span class="command"><strong>zone</strong></span> configuration unless
it is an <span class="command"><strong>in-view</strong></span> configuration. Its
acceptable values include: <code class="varname">delegation-only</code>,
<code class="varname">forward</code>, <code class="varname">hint</code>,
<code class="varname">master</code>, <code class="varname">redirect</code>,
<code class="varname">slave</code>, <code class="varname">static-stub</code>,
and <code class="varname">stub</code>.
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col class="1">
<col width="4.017in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p>
<code class="varname">master</code>
</p>
</td>
<td>
<p>
The server has a master copy of the data
for the zone and will be able to provide authoritative
answers for
it.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">slave</code>
</p>
</td>
<td>
<p>
A slave zone is a replica of a master
zone. The <span class="command"><strong>masters</strong></span> list
specifies one or more IP addresses
of master servers that the slave contacts to update
its copy of the zone.
Masters list elements can also be names of other
masters lists.
By default, transfers are made from port 53 on the
servers; this can
be changed for all servers by specifying a port number
before the
list of IP addresses, or on a per-server basis after
the IP address.
Authentication to the master can also be done with
per-server TSIG keys.
If a file is specified, then the
replica will be written to this file whenever the zone
is changed,
and reloaded from this file on a server restart. Use
of a file is
recommended, since it often speeds server startup and
eliminates
a needless waste of bandwidth. Note that for large
numbers (in the
tens or hundreds of thousands) of zones per server, it
is best to
use a two-level naming scheme for zone filenames. For
example,
a slave server for the zone <code class="literal">example.com</code> might place
the zone contents into a file called
<code class="filename">ex/example.com</code> where <code class="filename">ex/</code> is
just the first two letters of the zone name. (Most
operating systems
behave very slowly if you put 100000 files into
a single directory.)
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">stub</code>
</p>
</td>
<td>
<p>
A stub zone is similar to a slave zone,
except that it replicates only the NS records of a
master zone instead
of the entire zone. Stub zones are not a standard part
of the DNS;
they are a feature specific to the <acronym class="acronym">BIND</acronym> implementation.
</p>
<p>
Stub zones can be used to eliminate the need for glue
NS record
in a parent zone at the expense of maintaining a stub
zone entry and
a set of name server addresses in <code class="filename">named.conf</code>.
This usage is not recommended for new configurations,
and BIND 9
supports it only in a limited way.
In <acronym class="acronym">BIND</acronym> 4/8, zone
transfers of a parent zone
included the NS records from stub children of that
zone. This meant
that, in some cases, users could get away with
configuring child stubs
only in the master server for the parent zone. <acronym class="acronym">BIND</acronym>
9 never mixes together zone data from different zones
in this
way. Therefore, if a <acronym class="acronym">BIND</acronym> 9 master serving a parent
zone has child stub zones configured, all the slave
servers for the
parent zone also need to have the same child stub
zones
configured.
</p>
<p>
Stub zones can also be used as a way of forcing the
resolution
of a given domain to use a particular set of
authoritative servers.
For example, the caching name servers on a private
network using
RFC1918 addressing may be configured with stub zones
for
<code class="literal">10.in-addr.arpa</code>
to use a set of internal name servers as the
authoritative
servers for that domain.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">static-stub</code>
</p>
</td>
<td>
<p>
A static-stub zone is similar to a stub zone
with the following exceptions:
the zone data is statically configured, rather
than transferred from a master server;
when recursion is necessary for a query that
matches a static-stub zone, the locally
configured data (nameserver names and glue addresses)
is always used even if different authoritative
information is cached.
</p>
<p>
Zone data is configured via the
<span class="command"><strong>server-addresses</strong></span> and
<span class="command"><strong>server-names</strong></span> zone options.
</p>
<p>
The zone data is maintained in the form of NS
and (if necessary) glue A or AAAA RRs
internally, which can be seen by dumping zone
databases by <span class="command"><strong>rndc dumpdb -all</strong></span>.
The configured RRs are considered local configuration
parameters rather than public data.
Non recursive queries (i.e., those with the RD
bit off) to a static-stub zone are therefore
prohibited and will be responded with REFUSED.
</p>
<p>
Since the data is statically configured, no
zone maintenance action takes place for a static-stub
zone.
For example, there is no periodic refresh
attempt, and an incoming notify message
will be rejected with an rcode of NOTAUTH.
</p>
<p>
Each static-stub zone is configured with
internally generated NS and (if necessary)
glue A or AAAA RRs
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">forward</code>
</p>
</td>
<td>
<p>
A "forward zone" is a way to configure
forwarding on a per-domain basis. A <span class="command"><strong>zone</strong></span> statement
of type <span class="command"><strong>forward</strong></span> can
contain a <span class="command"><strong>forward</strong></span>
and/or <span class="command"><strong>forwarders</strong></span>
statement,
which will apply to queries within the domain given by
the zone
name. If no <span class="command"><strong>forwarders</strong></span>
statement is present or
an empty list for <span class="command"><strong>forwarders</strong></span> is given, then no
forwarding will be done for the domain, canceling the
effects of
any forwarders in the <span class="command"><strong>options</strong></span> statement. Thus
if you want to use this type of zone to change the
behavior of the
global <span class="command"><strong>forward</strong></span> option
(that is, "forward first"
to, then "forward only", or vice versa, but want to
use the same
servers as set globally) you need to re-specify the
global forwarders.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">hint</code>
</p>
</td>
<td>
<p>
The initial set of root name servers is
specified using a "hint zone". When the server starts
up, it uses
the root hints to find a root name server and get the
most recent
list of root name servers. If no hint zone is
specified for class
IN, the server uses a compiled-in default set of root
servers hints.
Classes other than IN have no built-in defaults hints.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">redirect</code>
</p>
</td>
<td>
<p>
Redirect zones are used to provide answers to
queries when normal resolution would result in
NXDOMAIN being returned.
Only one redirect zone is supported
per view. <span class="command"><strong>allow-query</strong></span> can be
used to restrict which clients see these answers.
</p>
<p>
If the client has requested DNSSEC records (DO=1) and
the NXDOMAIN response is signed then no substitution
will occur.
</p>
<p>
To redirect all NXDOMAIN responses to
100.100.100.2 and
2001:ffff:ffff::100.100.100.2, one would
configure a type redirect zone named ".",
with the zone file containing wildcard records
that point to the desired addresses:
<code class="literal">"*. IN A 100.100.100.2"</code>
and
<code class="literal">"*. IN AAAA 2001:ffff:ffff::100.100.100.2"</code>.
</p>
<p>
To redirect all Spanish names (under .ES) one
would use similar entries but with the names
"*.ES." instead of "*.". To redirect all
commercial Spanish names (under COM.ES) one
would use wildcard entries called "*.COM.ES.".
</p>
<p>
Note that the redirect zone supports all
possible types; it is not limited to A and
AAAA records.
</p>
<p>
Because redirect zones are not referenced
directly by name, they are not kept in the
zone lookup table with normal master and slave
zones. Consequently, it is not currently possible
to use
<span class="command"><strong>rndc reload
<em class="replaceable"><code>zonename</code></em></strong></span>
to reload a redirect zone. However, when using
<span class="command"><strong>rndc reload</strong></span> without specifying
a zone name, redirect zones will be reloaded along
with other zones.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">delegation-only</code>
</p>
</td>
<td>
<p>
This is used to enforce the delegation-only
status of infrastructure zones (e.g. COM,
NET, ORG). Any answer that is received
without an explicit or implicit delegation
in the authority section will be treated
as NXDOMAIN. This does not apply to the
zone apex. This should not be applied to
leaf zones.
</p>
<p>
<code class="varname">delegation-only</code> has no
effect on answers received from forwarders.
</p>
<p>
See caveats in <a class="xref" href="Bv9ARM.ch06.html#root_delegation_only"><span class="command"><strong>root-delegation-only</strong></span></a>.
</p>
</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>
<p>
The zone's name may optionally be followed by a class. If
a class is not specified, class <code class="literal">IN</code> (for <code class="varname">Internet</code>),
is assumed. This is correct for the vast majority of cases.
</p>
<p>
The <code class="literal">hesiod</code> class is
named for an information service from MIT's Project Athena. It
is
used to share information about various systems databases, such
as users, groups, printers and so on. The keyword
<code class="literal">HS</code> is
a synonym for hesiod.
</p>
<p>
Another MIT development is Chaosnet, a LAN protocol created
in the mid-1970s. Zone data for it can be specified with the <code class="literal">CHAOS</code> class.
</p>
</div>
<div class="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><span class="term"><span class="command"><strong>allow-notify</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>allow-notify</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called “Access Control”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-query</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>allow-query</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called “Access Control”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-query-on</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>allow-query-on</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called “Access Control”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-transfer</strong></span></span></dt>
<dd>
<p>
See the description of <span class="command"><strong>allow-transfer</strong></span>
in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called “Access Control”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-update</strong></span></span></dt>
<dd>
<p>
See the description of <span class="command"><strong>allow-update</strong></span>
in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called “Access Control”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>update-policy</strong></span></span></dt>
<dd>
<p>
Specifies a "Simple Secure Update" policy. See
<a class="xref" href="Bv9ARM.ch06.html#dynamic_update_policies" title="Dynamic Update Policies">the section called “Dynamic Update Policies”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>allow-update-forwarding</strong></span></span></dt>
<dd>
<p>
See the description of <span class="command"><strong>allow-update-forwarding</strong></span>
in <a class="xref" href="Bv9ARM.ch06.html#access_control" title="Access Control">the section called “Access Control”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>also-notify</strong></span></span></dt>
<dd>
<p>
Only meaningful if <span class="command"><strong>notify</strong></span>
is
active for this zone. The set of machines that will
receive a
<code class="literal">DNS NOTIFY</code> message
for this zone is made up of all the listed name servers
(other than
the primary master) for the zone plus any IP addresses
specified
with <span class="command"><strong>also-notify</strong></span>. A port
may be specified
with each <span class="command"><strong>also-notify</strong></span>
address to send the notify
messages to a port other than the default of 53.
A TSIG key may also be specified to cause the
<code class="literal">NOTIFY</code> to be signed by the
given key.
<span class="command"><strong>also-notify</strong></span> is not
meaningful for stub zones.
The default is the empty list.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-names</strong></span></span></dt>
<dd>
<p>
This option is used to restrict the character set and
syntax of
certain domain names in master files and/or DNS responses
received from the
network. The default varies according to zone type. For <span class="command"><strong>master</strong></span> zones the default is <span class="command"><strong>fail</strong></span>. For <span class="command"><strong>slave</strong></span>
zones the default is <span class="command"><strong>warn</strong></span>.
It is not implemented for <span class="command"><strong>hint</strong></span> zones.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-mx</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>check-mx</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-spf</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>check-spf</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-wildcard</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>check-wildcard</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-integrity</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>check-integrity</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>check-sibling</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>check-sibling</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>zero-no-soa-ttl</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>zero-no-soa-ttl</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>update-check-ksk</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>update-check-ksk</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-loadkeys-interval</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>dnssec-loadkeys-interval</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called “<span class="command"><strong>options</strong></span> Statement Definition and
Usage”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-update-mode</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>dnssec-update-mode</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called “<span class="command"><strong>options</strong></span> Statement Definition and
Usage”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-dnskey-kskonly</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>dnssec-dnskey-kskonly</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>try-tcp-refresh</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>try-tcp-refresh</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>database</strong></span></span></dt>
<dd>
<p>
Specify the type of database to be used for storing the
zone data. The string following the <span class="command"><strong>database</strong></span> keyword
is interpreted as a list of whitespace-delimited words.
The first word
identifies the database type, and any subsequent words are
passed
as arguments to the database to be interpreted in a way
specific
to the database type.
</p>
<p>
The default is <strong class="userinput"><code>"rbt"</code></strong>, BIND 9's
native in-memory
red-black-tree database. This database does not take
arguments.
</p>
<p>
Other values are possible if additional database drivers
have been linked into the server. Some sample drivers are
included
with the distribution but none are linked in by default.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dialup</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>dialup</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>delegation-only</strong></span></span></dt>
<dd>
<p>
The flag only applies to forward, hint and stub
zones. If set to <strong class="userinput"><code>yes</code></strong>,
then the zone will also be treated as if it is
also a delegation-only type zone.
</p>
<p>
See caveats in <a class="xref" href="Bv9ARM.ch06.html#root_delegation_only"><span class="command"><strong>root-delegation-only</strong></span></a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>file</strong></span></span></dt>
<dd>
<p>
Set the zone's filename. In <span class="command"><strong>master</strong></span>,
<span class="command"><strong>hint</strong></span>, and <span class="command"><strong>redirect</strong></span>
zones which do not have <span class="command"><strong>masters</strong></span>
defined, zone data is loaded from this file. In
<span class="command"><strong>slave</strong></span>, <span class="command"><strong>stub</strong></span>, and
<span class="command"><strong>redirect</strong></span> zones which do have
<span class="command"><strong>masters</strong></span> defined, zone data is
retrieved from another server and saved in this file.
This option is not applicable to other zone types.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>forward</strong></span></span></dt>
<dd>
<p>
Only meaningful if the zone has a forwarders
list. The <span class="command"><strong>only</strong></span> value causes
the lookup to fail
after trying the forwarders and getting no answer, while <span class="command"><strong>first</strong></span> would
allow a normal lookup to be tried.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>forwarders</strong></span></span></dt>
<dd>
<p>
Used to override the list of global forwarders.
If it is not specified in a zone of type <span class="command"><strong>forward</strong></span>,
no forwarding is done for the zone and the global options are
not used.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>ixfr-base</strong></span></span></dt>
<dd>
<p>
Was used in <acronym class="acronym">BIND</acronym> 8 to
specify the name
of the transaction log (journal) file for dynamic update
and IXFR.
<acronym class="acronym">BIND</acronym> 9 ignores the option
and constructs the name of the journal
file by appending "<code class="filename">.jnl</code>"
to the name of the
zone file.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>ixfr-tmp-file</strong></span></span></dt>
<dd>
<p>
Was an undocumented option in <acronym class="acronym">BIND</acronym> 8.
Ignored in <acronym class="acronym">BIND</acronym> 9.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>journal</strong></span></span></dt>
<dd>
<p>
Allow the default journal's filename to be overridden.
The default is the zone's filename with "<code class="filename">.jnl</code>" appended.
This is applicable to <span class="command"><strong>master</strong></span> and <span class="command"><strong>slave</strong></span> zones.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-journal-size</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>max-journal-size</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#server_resource_limits" title="Server Resource Limits">the section called “Server Resource Limits”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-records</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>max-records</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#server_resource_limits" title="Server Resource Limits">the section called “Server Resource Limits”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-transfer-time-in</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>max-transfer-time-in</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-transfer-idle-in</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>max-transfer-idle-in</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-transfer-time-out</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>max-transfer-time-out</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-transfer-idle-out</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>max-transfer-idle-out</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>notify</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>notify</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>notify-delay</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>notify-delay</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called “Tuning”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>notify-to-soa</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>notify-to-soa</strong></span> in
<a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>pubkey</strong></span></span></dt>
<dd>
<p>
In <acronym class="acronym">BIND</acronym> 8, this option was
intended for specifying
a public zone key for verification of signatures in DNSSEC
signed
zones when they are loaded from disk. <acronym class="acronym">BIND</acronym> 9 does not verify signatures
on load and ignores the option.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>zone-statistics</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>zone-statistics</strong></span> in
<a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called “<span class="command"><strong>options</strong></span> Statement Definition and
Usage”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>server-addresses</strong></span></span></dt>
<dd>
<p>
Only meaningful for static-stub zones.
This is a list of IP addresses to which queries
should be sent in recursive resolution for the
zone.
A non empty list for this option will internally
configure the apex NS RR with associated glue A or
AAAA RRs.
</p>
<p>
For example, if "example.com" is configured as a
static-stub zone with 192.0.2.1 and 2001:db8::1234
in a <span class="command"><strong>server-addresses</strong></span> option,
the following RRs will be internally configured.
</p>
<pre class="programlisting">example.com. NS example.com.
example.com. A 192.0.2.1
example.com. AAAA 2001:db8::1234</pre>
<p>
These records are internally used to resolve
names under the static-stub zone.
For instance, if the server receives a query for
"www.example.com" with the RD bit on, the server
will initiate recursive resolution and send
queries to 192.0.2.1 and/or 2001:db8::1234.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>server-names</strong></span></span></dt>
<dd>
<p>
Only meaningful for static-stub zones.
This is a list of domain names of nameservers that
act as authoritative servers of the static-stub
zone.
These names will be resolved to IP addresses when
<span class="command"><strong>named</strong></span> needs to send queries to
these servers.
To make this supplemental resolution successful,
these names must not be a subdomain of the origin
name of static-stub zone.
That is, when "example.net" is the origin of a
static-stub zone, "ns.example" and
"master.example.com" can be specified in the
<span class="command"><strong>server-names</strong></span> option, but
"ns.example.net" cannot, and will be rejected by
the configuration parser.
</p>
<p>
A non empty list for this option will internally
configure the apex NS RR with the specified names.
For example, if "example.com" is configured as a
static-stub zone with "ns1.example.net" and
"ns2.example.net"
in a <span class="command"><strong>server-names</strong></span> option,
the following RRs will be internally configured.
</p>
<pre class="programlisting">example.com. NS ns1.example.net.
example.com. NS ns2.example.net.
</pre>
<p>
These records are internally used to resolve
names under the static-stub zone.
For instance, if the server receives a query for
"www.example.com" with the RD bit on, the server
initiate recursive resolution,
resolve "ns1.example.net" and/or
"ns2.example.net" to IP addresses, and then send
queries to (one or more of) these addresses.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>sig-validity-interval</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>sig-validity-interval</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called “Tuning”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>sig-signing-nodes</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>sig-signing-nodes</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called “Tuning”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>sig-signing-signatures</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>sig-signing-signatures</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called “Tuning”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>sig-signing-type</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>sig-signing-type</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called “Tuning”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>transfer-source</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>transfer-source</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>transfer-source-v6</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>transfer-source-v6</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>alt-transfer-source</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>alt-transfer-source</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>alt-transfer-source-v6</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>alt-transfer-source-v6</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>use-alt-transfer-source</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>use-alt-transfer-source</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>notify-source</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>notify-source</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>notify-source-v6</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>notify-source-v6</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>.
</p>
</dd>
<dt>
<span class="term"><span class="command"><strong>min-refresh-time</strong></span>, </span><span class="term"><span class="command"><strong>max-refresh-time</strong></span>, </span><span class="term"><span class="command"><strong>min-retry-time</strong></span>, </span><span class="term"><span class="command"><strong>max-retry-time</strong></span></span>
</dt>
<dd>
<p>
See the description in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called “Tuning”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>ixfr-from-differences</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>ixfr-from-differences</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
(Note that the <span class="command"><strong>ixfr-from-differences</strong></span>
<strong class="userinput"><code>master</code></strong> and
<strong class="userinput"><code>slave</code></strong> choices are not
available at the zone level.)
</p>
</dd>
<dt><span class="term"><span class="command"><strong>key-directory</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>key-directory</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called “<span class="command"><strong>options</strong></span> Statement Definition and
Usage”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>auto-dnssec</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>auto-dnssec</strong></span> in
<a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called “<span class="command"><strong>options</strong></span> Statement Definition and
Usage”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>serial-update-method</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>serial-update-method</strong></span> in
<a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called “<span class="command"><strong>options</strong></span> Statement Definition and
Usage”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>inline-signing</strong></span></span></dt>
<dd>
<p>
If <code class="literal">yes</code>, this enables
"bump in the wire" signing of a zone, where a
unsigned zone is transferred in or loaded from
disk and a signed version of the zone is served,
with possibly, a different serial number. This
behavior is disabled by default.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>multi-master</strong></span></span></dt>
<dd>
<p>
See the description of <span class="command"><strong>multi-master</strong></span> in
<a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>masterfile-format</strong></span></span></dt>
<dd>
<p>
See the description of <span class="command"><strong>masterfile-format</strong></span>
in <a class="xref" href="Bv9ARM.ch06.html#tuning" title="Tuning">the section called “Tuning”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>max-zone-ttl</strong></span></span></dt>
<dd>
<p>
See the description of <span class="command"><strong>max-zone-ttl</strong></span>
in <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called “<span class="command"><strong>options</strong></span> Statement Definition and
Usage”</a>.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>dnssec-secure-to-insecure</strong></span></span></dt>
<dd>
<p>
See the description of
<span class="command"><strong>dnssec-secure-to-insecure</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a>.
</p>
</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>
<p><acronym class="acronym">BIND</acronym> 9 supports two alternative
methods of granting clients the right to perform
dynamic updates to a zone, configured by the
<span class="command"><strong>allow-update</strong></span> and
<span class="command"><strong>update-policy</strong></span> option, respectively.
</p>
<p>
The <span class="command"><strong>allow-update</strong></span> clause is a simple
access control list. Any client that matches
the ACL is granted permission to update any record
in the zone.
</p>
<p>
The <span class="command"><strong>update-policy</strong></span> clause
allows more fine-grained control over what updates are
allowed. It specifies a set of rules, in which each rule
either grants or denies permission for one or more
names in the zone to be updated by one or more
identities. Identity is determined by the key that
signed the update request using either TSIG or SIG(0).
In most cases, <span class="command"><strong>update-policy</strong></span> rules
only apply to key-based identities. There is no way
to specify update permissions based on client source
address.
</p>
<p>
<span class="command"><strong>update-policy</strong></span> rules are only meaningful
for zones of type <span class="command"><strong>master</strong></span>, and are
not allowed in any other zone type.
It is a configuration error to specify both
<span class="command"><strong>allow-update</strong></span> and
<span class="command"><strong>update-policy</strong></span> at the same time.
</p>
<p>
A pre-defined <span class="command"><strong>update-policy</strong></span> rule can be
switched on with the command
<span class="command"><strong>update-policy local;</strong></span>.
Using this in a zone causes
<span class="command"><strong>named</strong></span> to generate a TSIG session key
when starting up and store it in a file; this key can then
be used by local clients to update the zone while
<span class="command"><strong>named</strong></span> 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
<span class="command"><strong>session-keyfile</strong></span>,
<span class="command"><strong>session-keyname</strong></span> and
<span class="command"><strong>session-keyalg</strong></span> options, respectively.
A client running on the local system, if run with appropriate
permissions, may read the session key from the key file and
use it to sign update requests. The zone's update
policy will be set to allow that key to change any record
within the zone. Assuming the key name is "local-ddns",
this policy is equivalent to:
</p>
<pre class="programlisting">update-policy { grant local-ddns zonesub any; };
</pre>
<p>
...with the additional restriction that only clients
connecting from the local system will be permitted to send
updates.
</p>
<p>
Note that only one session key is generated by
<span class="command"><strong>named</strong></span>; all zones configured to use
<span class="command"><strong>update-policy local</strong></span> will accept the same key.
</p>
<p>
The command <span class="command"><strong>nsupdate -l</strong></span> implements this
feature, sending requests to localhost and signing them using
the key retrieved from the session key file.
</p>
<p>
Other rule definitions look like this:
</p>
<pre class="programlisting">
( <span class="command"><strong>grant</strong></span> | <span class="command"><strong>deny</strong></span> ) <em class="replaceable"><code>identity</code></em> <em class="replaceable"><code>ruletype</code></em> [<span class="optional"> <em class="replaceable"><code>name</code></em> </span>] [<span class="optional"> <em class="replaceable"><code>types</code></em> </span>]
</pre>
<p>
Each rule grants or denies privileges. Rules are checked
in the order in which they are specified in the
<span class="command"><strong>update-policy</strong></span> 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
<span class="command"><strong>ruletype</strong></span> field, and the interpretation
of other fields varies depending on the rule type.
</p>
<p>
In general, a rule is matched when the
key that signed an update request matches the
<span class="command"><strong>identity</strong></span> field, the name of the record
to be updated matches the <span class="command"><strong>name</strong></span> field
(in the manner specified by the <span class="command"><strong>ruletype</strong></span>
field), and the type of the record to be updated matches the
<span class="command"><strong>types</strong></span> field. Details for each rule type
are described below.
</p>
<p>
The <span class="command"><strong>identity</strong></span> field must be set to
a fully-qualified domain name. In most cases, this
represensts the name of the TSIG or SIG(0) key that must be
used to sign the update request. If the specified name is a
wildcard, it is subject to DNS wildcard expansion, and the
rule may apply to multiple identities. When a TKEY exchange
has been used to create a shared secret, the identity of
the key used to authenticate the TKEY exchange will be
used as the identity of the shared secret. Some rule types
use identities matching the client's Kerberos principal
(e.g, <strong class="userinput"><code>"host/machine@REALM"</code></strong>) or
Windows realm (<strong class="userinput"><code>machine$@REALM</code></strong>).
</p>
<p>
The <em class="replaceable"><code>name</code></em> 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.
</p>
<p>
If no <span class="command"><strong>types</strong></span> 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.
</p>
<p>
The <em class="replaceable"><code>ruletype</code></em> field has 16
values:
<code class="varname">name</code>, <code class="varname">subdomain</code>,
<code class="varname">wildcard</code>, <code class="varname">self</code>,
<code class="varname">selfsub</code>, <code class="varname">selfwild</code>,
<code class="varname">krb5-self</code>, <code class="varname">ms-self</code>,
<code class="varname">krb5-selfsub</code>, <code class="varname">ms-selfsub</code>,
<code class="varname">krb5-subdomain</code>,
<code class="varname">ms-subdomain</code>,
<code class="varname">tcp-self</code>, <code class="varname">6to4-self</code>,
<code class="varname">zonesub</code>, and <code class="varname">external</code>.
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="0.819in" class="1">
<col width="3.681in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p>
<code class="varname">name</code>
</p>
</td>
<td>
<p>
Exact-match semantics. This rule matches
when the name being updated is identical
to the contents of the
<em class="replaceable"><code>name</code></em> field.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">subdomain</code>
</p>
</td>
<td>
<p>
This rule matches when the name being updated
is a subdomain of, or identical to, the
contents of the <em class="replaceable"><code>name</code></em>
field.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">zonesub</code>
</p>
</td>
<td>
<p>
This rule is similar to subdomain, except that
it matches when the name being updated is a
subdomain of the zone in which the
<span class="command"><strong>update-policy</strong></span> statement
appears. This obviates the need to type the zone
name twice, and enables the use of a standard
<span class="command"><strong>update-policy</strong></span> statement in
multiple zones without modification.
</p>
<p>
When this rule is used, the
<em class="replaceable"><code>name</code></em> field is omitted.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">wildcard</code>
</p>
</td>
<td>
<p>
The <em class="replaceable"><code>name</code></em> field
is subject to DNS wildcard expansion, and
this rule matches when the name being updated
is a valid expansion of the wildcard.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">self</code>
</p>
</td>
<td>
<p>
This rule matches when the name of the record
being updated matches the contents of the
<em class="replaceable"><code>identity</code></em> field.
The <em class="replaceable"><code>name</code></em> field
is ignored. To avoid confusion, it is recommended
that this field be set to the same value as the
<em class="replaceable"><code>identity</code></em> field or to
"."
</p>
<p>
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 <em class="replaceable"><code>identity</code></em> field
can be specified as <code class="constant">*</code>
(an asterisk).
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">selfsub</code>
</p>
</td>
<td>
<p>
This rule is similar to <code class="varname">self</code>
except that subdomains of <code class="varname">self</code>
can also be updated.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">selfwild</code>
</p>
</td>
<td>
<p>
This rule is similar to <code class="varname">self</code>
except that only subdomains of
<code class="varname">self</code> can be updated.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">ms-self</code>
</p>
</td>
<td>
<p>
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.
</p>
<p>
The realm to be matched is specified in the
<em class="replaceable"><code>identity</code></em> field.
</p>
<p>
The <em class="replaceable"><code>name</code></em> field has
no effect on this rule; it should be set to "."
as a placeholder.
</p>
<p>
For example,
<strong class="userinput"><code>grant EXAMPLE.COM ms-self . A AAAA</code></strong>
allows any machine with a valid principal in
the realm <strong class="userinput"><code>EXAMPLE.COM</code></strong> to update
its own address records.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">ms-selfsub</code>
</p>
</td>
<td>
<p>
This is similar to <span class="command"><strong>ms-self</strong></span>
except it also allows updates to any subdomain of
the name specified in the Windows machine
principal, not just to the name itself.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">ms-subdomain</code>
</p>
</td>
<td>
<p>
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.
</p>
<p>
The realm to be matched is specified in the
<em class="replaceable"><code>identity</code></em> field.
</p>
<p>
The <em class="replaceable"><code>name</code></em> 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.
</p>
<p>
For example, if <span class="command"><strong>update-policy</strong></span>
for the zone "example.com" includes
<strong class="userinput"><code>grant EXAMPLE.COM ms-subdomain hosts.example.com. A AAAA</code></strong>,
any machine with a valid principal in
the realm <strong class="userinput"><code>EXAMPLE.COM</code></strong> will
be able to update address records at or below
"hosts.example.com".
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">krb5-self</code>
</p>
</td>
<td>
<p>
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 <span class="command"><strong>ms-self</strong></span> due to the
'machine' part of the Kerberos principal
being an absolute name instead of a unqualified
name.
</p>
<p>
The realm to be matched is specified in the
<em class="replaceable"><code>identity</code></em> field.
</p>
<p>
The <em class="replaceable"><code>name</code></em> field has
no effect on this rule; it should be set to "."
as a placeholder.
</p>
<p>
For example,
<strong class="userinput"><code>grant EXAMPLE.COM krb5-self . A AAAA</code></strong>
allows any machine with a valid principal in
the realm <strong class="userinput"><code>EXAMPLE.COM</code></strong> to update
its own address records.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">krb5-selfsub</code>
</p>
</td>
<td>
<p>
This is similar to <span class="command"><strong>krb5-self</strong></span>
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.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">krb5-subdomain</code>
</p>
</td>
<td>
<p>
This rule is identical to
<span class="command"><strong>ms-subdomain</strong></span>, except that it works
with Kerberos machine principals (i.e.,
'host/machine@REALM') rather than Windows machine
principals.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">tcp-self</code>
</p>
</td>
<td>
<p>
This rule allows updates that have been sent via
TCP and for which the standard mapping from the
client's IP address into the
<code class="literal">in-addr.arpa</code> and
<code class="literal">ip6.arpa</code>
namespaces match the name to be updated.
The <span class="command"><strong>identity</strong></span> field must match
that name. The <span class="command"><strong>name</strong></span> 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.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
It is theoretically possible to spoof these TCP
sessions.
</div>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">6to4-self</code>
</p>
</td>
<td>
<p>
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.
</p>
<p>
The <span class="command"><strong>identity</strong></span> field must match
the 6to4 prefix in <code class="literal">ip6.arpa</code>.
The <span class="command"><strong>name</strong></span> 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.
</p>
<p>
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>.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
It is theoretically possible to spoof these TCP
sessions.
</div>
</td>
</tr>
<tr>
<td>
<p>
<code class="varname">external</code>
</p>
</td>
<td>
<p>
This rule allows <span class="command"><strong>named</strong></span>
to defer the decision of whether to allow a
given update to an external daemon.
</p>
<p>
The method of communicating with the daemon is
specified in the <em class="replaceable"><code>identity</code></em>
field, the format of which is
"<code class="constant">local:</code><em class="replaceable"><code>path</code></em>",
where <em class="replaceable"><code>path</code></em> is the location
of a UNIX-domain socket. (Currently, "local" is the
only supported mechanism.)
</p>
<p>
Requests to the external daemon are sent over the
UNIX-domain socket as datagrams with the following
format:
</p>
<pre class="programlisting">
Protocol version number (4 bytes, network byte order, currently 1)
Request length (4 bytes, network byte order)
Signer (null-terminated string)
Name (null-terminated string)
TCP source address (null-terminated string)
Rdata type (null-terminated string)
Key (null-terminated string)
TKEY token length (4 bytes, network byte order)
TKEY token (remainder of packet)</pre>
<p>
The daemon replies with a four-byte value in
network byte order, containing either 0 or 1; 0
indicates that the specified update is not
permitted, and 1 indicates that it is.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="multiple_views"></a>Multiple views</h4></div></div></div>
<p>
When multiple views are in use, a zone may be
referenced by more than one of them. Often, the views
will contain different zones with the same name, allowing
different clients to receive different answers for the same
queries. At times, however, it is desirable for multiple
views to contain identical zones. The
<span class="command"><strong>in-view</strong></span> 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:
</p>
<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>
<p>
An <span class="command"><strong>in-view</strong></span> option cannot refer to a view
that is configured later in the configuration file.
</p>
<p>
A <span class="command"><strong>zone</strong></span> statement which uses the
<span class="command"><strong>in-view</strong></span> option may not use any other
options with the exception of <span class="command"><strong>forward</strong></span>
and <span class="command"><strong>forwarders</strong></span>. (These options control
the behavior of the containing view, rather than changing
the zone object itself.)
</p>
<p>
Zone level acls (e.g. allow-query, allow-transfer) and
other configuration details of the zone are all set
in the view the referenced zone is defined in. Care
need to be taken to ensure that acls are wide enough
for all views referencing the zone.
</p>
<p>
An <span class="command"><strong>in-view</strong></span> zone cannot be used as a
response policy zone.
</p>
<p>
An <span class="command"><strong>in-view</strong></span> zone is not intended to reference
a <span class="command"><strong>forward</strong></span> zone.
</p>
</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>
<p>
This section, largely borrowed from RFC 1034, describes the
concept of a Resource Record (RR) and explains when each is used.
Since the publication of RFC 1034, several new RRs have been
identified
and implemented in the DNS. These are also included.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.7.6.2.3"></a>Resource Records</h4></div></div></div>
<p>
A domain name identifies a node. Each node has a set of
resource information, which may be empty. The set of resource
information associated with a particular name is composed of
separate RRs. The order of RRs in a set is not significant and
need not be preserved by name servers, resolvers, or other
parts of the DNS. However, sorting of multiple RRs is
permitted for optimization purposes, for example, to specify
that a particular nearby server be tried first. See <a class="xref" href="Bv9ARM.ch06.html#the_sortlist_statement" title="The sortlist Statement">the section called “The <span class="command"><strong>sortlist</strong></span> Statement”</a> and <a class="xref" href="Bv9ARM.ch06.html#rrset_ordering" title="RRset Ordering">the section called “RRset Ordering”</a>.
</p>
<p>
The components of a Resource Record are:
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.000in" class="1">
<col width="3.500in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p>
owner name
</p>
</td>
<td>
<p>
The domain name where the RR is found.
</p>
</td>
</tr>
<tr>
<td>
<p>
type
</p>
</td>
<td>
<p>
An encoded 16-bit value that specifies
the type of the resource record.
</p>
</td>
</tr>
<tr>
<td>
<p>
TTL
</p>
</td>
<td>
<p>
The time-to-live of the RR. This field
is a 32-bit integer in units of seconds, and is
primarily used by
resolvers when they cache RRs. The TTL describes how
long a RR can
be cached before it should be discarded.
</p>
</td>
</tr>
<tr>
<td>
<p>
class
</p>
</td>
<td>
<p>
An encoded 16-bit value that identifies
a protocol family or instance of a protocol.
</p>
</td>
</tr>
<tr>
<td>
<p>
RDATA
</p>
</td>
<td>
<p>
The resource data. The format of the
data is type (and sometimes class) specific.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
The following are <span class="emphasis"><em>types</em></span> of valid RRs:
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="0.875in" class="1">
<col width="3.625in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p>
A
</p>
</td>
<td>
<p>
A host address. In the IN class, this is a
32-bit IP address. Described in RFC 1035.
</p>
</td>
</tr>
<tr>
<td>
<p>
AAAA
</p>
</td>
<td>
<p>
IPv6 address. Described in RFC 1886.
</p>
</td>
</tr>
<tr>
<td>
<p>
A6
</p>
</td>
<td>
<p>
IPv6 address. This can be a partial
address (a suffix) and an indirection to the name
where the rest of the
address (the prefix) can be found. Experimental.
Described in RFC 2874.
</p>
</td>
</tr>
<tr>
<td>
<p>
AFSDB
</p>
</td>
<td>
<p>
Location of AFS database servers.
Experimental. Described in RFC 1183.
</p>
</td>
</tr>
<tr>
<td>
<p>
APL
</p>
</td>
<td>
<p>
Address prefix list. Experimental.
Described in RFC 3123.
</p>
</td>
</tr>
<tr>
<td>
<p>
ATMA
</p>
</td>
<td>
<p>
ATM Address.
</p>
</td>
</tr>
<tr>
<td>
<p>
AVC
</p>
</td>
<td>
<p>
Application Visibility and Control record.
</p>
</td>
</tr>
<tr>
<td>
<p>
CAA
</p>
</td>
<td>
<p>
Identifies which Certificate Authorities can issue
certificates for this domain and what rules they
need to follow when doing so. Defined in RFC 6844.
</p>
</td>
</tr>
<tr>
<td>
<p>
CDNSKEY
</p>
</td>
<td>
<p>
Identifies which DNSKEY records should be published
as DS records in the parent zone.
</p>
</td>
</tr>
<tr>
<td>
<p>
CDS
</p>
</td>
<td>
<p>
Contains the set of DS records that should be published
by the parent zone.
</p>
</td>
</tr>
<tr>
<td>
<p>
CERT
</p>
</td>
<td>
<p>
Holds a digital certificate.
Described in RFC 2538.
</p>
</td>
</tr>
<tr>
<td>
<p>
CNAME
</p>
</td>
<td>
<p>
Identifies the canonical name of an alias.
Described in RFC 1035.
</p>
</td>
</tr>
<tr>
<td>
<p>
CSYNC
</p>
</td>
<td>
<p>
Child-to-Parent Synchronization in DNS as described
in RFC 7477.
</p>
</td>
</tr>
<tr>
<td>
<p>
DHCID
</p>
</td>
<td>
<p>
Is used for identifying which DHCP client is
associated with this name. Described in RFC 4701.
</p>
</td>
</tr>
<tr>
<td>
<p>
DLV
</p>
</td>
<td>
<p>
A DNS Look-aside Validation record which contains
the records that are used as trust anchors for
zones in a DLV namespace. Described in RFC 4431.
</p>
</td>
</tr>
<tr>
<td>
<p>
DNAME
</p>
</td>
<td>
<p>
Replaces the domain name specified with
another name to be looked up, effectively aliasing an
entire
subtree of the domain name space rather than a single
record
as in the case of the CNAME RR.
Described in RFC 2672.
</p>
</td>
</tr>
<tr>
<td>
<p>
DNSKEY
</p>
</td>
<td>
<p>
Stores a public key associated with a signed
DNS zone. Described in RFC 4034.
</p>
</td>
</tr>
<tr>
<td>
<p>
DOA
</p>
</td>
<td>
<p>
Implements the Digital Object Architecture over
DNS. Experimental.
</p>
</td>
</tr>
<tr>
<td>
<p>
DS
</p>
</td>
<td>
<p>
Stores the hash of a public key associated with a
signed DNS zone. Described in RFC 4034.
</p>
</td>
</tr>
<tr>
<td>
<p>
EID
</p>
</td>
<td>
<p>
End Point Identifier.
</p>
</td>
</tr>
<tr>
<td>
<p>
EUI48
</p>
</td>
<td>
<p>
A 48-bit EUI address. Described in RFC 7043.
</p>
</td>
</tr>
<tr>
<td>
<p>
EUI64
</p>
</td>
<td>
<p>
A 64-bit EUI address. Described in RFC 7043.
</p>
</td>
</tr>
<tr>
<td>
<p>
GID
</p>
</td>
<td>
<p>
Reserved.
</p>
</td>
</tr>
<tr>
<td>
<p>
GPOS
</p>
</td>
<td>
<p>
Specifies the global position. Superseded by LOC.
</p>
</td>
</tr>
<tr>
<td>
<p>
HINFO
</p>
</td>
<td>
<p>
Identifies the CPU and OS used by a host.
Described in RFC 1035.
</p>
</td>
</tr>
<tr>
<td>
<p>
HIP
</p>
</td>
<td>
<p>
Host Identity Protocol Address.
Described in RFC 5205.
</p>
</td>
</tr>
<tr>
<td>
<p>
IPSECKEY
</p>
</td>
<td>
<p>
Provides a method for storing IPsec keying material in
DNS. Described in RFC 4025.
</p>
</td>
</tr>
<tr>
<td>
<p>
ISDN
</p>
</td>
<td>
<p>
Representation of ISDN addresses.
Experimental. Described in RFC 1183.
</p>
</td>
</tr>
<tr>
<td>
<p>
KEY
</p>
</td>
<td>
<p>
Stores a public key associated with a
DNS name. Used in original DNSSEC; replaced
by DNSKEY in DNSSECbis, but still used with
SIG(0). Described in RFCs 2535 and 2931.
</p>
</td>
</tr>
<tr>
<td>
<p>
KX
</p>
</td>
<td>
<p>
Identifies a key exchanger for this
DNS name. Described in RFC 2230.
</p>
</td>
</tr>
<tr>
<td>
<p>
L32
</p>
</td>
<td>
<p>
Holds 32-bit Locator values for
Identifier-Locator Network Protocol. Described
in RFC 6742.
</p>
</td>
</tr>
<tr>
<td>
<p>
L64
</p>
</td>
<td>
<p>
Holds 64-bit Locator values for
Identifier-Locator Network Protocol. Described
in RFC 6742.
</p>
</td>
</tr>
<tr>
<td>
<p>
LOC
</p>
</td>
<td>
<p>
For storing GPS info. Described in RFC 1876.
Experimental.
</p>
</td>
</tr>
<tr>
<td>
<p>
LP
</p>
</td>
<td>
<p>
Identifier-Locator Network Protocol.
Described in RFC 6742.
</p>
</td>
</tr>
<tr>
<td>
<p>
MB
</p>
</td>
<td>
<p>
Mail Box. Historical.
</p>
</td>
</tr>
<tr>
<td>
<p>
MD
</p>
</td>
<td>
<p>
Mail Destination. Historical.
</p>
</td>
</tr>
<tr>
<td>
<p>
MF
</p>
</td>
<td>
<p>
Mail Forwarder. Historical.
</p>
</td>
</tr>
<tr>
<td>
<p>
MG
</p>
</td>
<td>
<p>
Mail Group. Historical.
</p>
</td>
</tr>
<tr>
<td>
<p>
MINFO
</p>
</td>
<td>
<p>
Mail Information.
</p>
</td>
</tr>
<tr>
<td>
<p>
MR
</p>
</td>
<td>
<p>
Mail Rename. Historical.
</p>
</td>
</tr>
<tr>
<td>
<p>
MX
</p>
</td>
<td>
<p>
Identifies a mail exchange for the domain with
a 16-bit preference value (lower is better)
followed by the host name of the mail exchange.
Described in RFC 974, RFC 1035.
</p>
</td>
</tr>
<tr>
<td>
<p>
NAPTR
</p>
</td>
<td>
<p>
Name authority pointer. Described in RFC 2915.
</p>
</td>
</tr>
<tr>
<td>
<p>
NID
</p>
</td>
<td>
<p>
Holds values for Node Identifiers in
Identifier-Locator Network Protocol. Described
in RFC 6742.
</p>
</td>
</tr>
<tr>
<td>
<p>
NINFO
</p>
</td>
<td>
<p>
Contains zone status information.
</p>
</td>
</tr>
<tr>
<td>
<p>
NIMLOC
</p>
</td>
<td>
<p>
Nimrod Locator.
</p>
</td>
</tr>
<tr>
<td>
<p>
NSAP
</p>
</td>
<td>
<p>
A network service access point.
Described in RFC 1706.
</p>
</td>
</tr>
<tr>
<td>
<p>
NSAP-PTR
</p>
</td>
<td>
<p>
Historical.
</p>
</td>
</tr>
<tr>
<td>
<p>
NS
</p>
</td>
<td>
<p>
The authoritative name server for the
domain. Described in RFC 1035.
</p>
</td>
</tr>
<tr>
<td>
<p>
NSEC
</p>
</td>
<td>
<p>
Used in DNSSECbis to securely indicate that
RRs with an owner name in a certain name interval do
not exist in
a zone and indicate what RR types are present for an
existing name.
Described in RFC 4034.
</p>
</td>
</tr>
<tr>
<td>
<p>
NSEC3
</p>
</td>
<td>
<p>
Used in DNSSECbis to securely indicate that
RRs with an owner name in a certain name
interval do not exist in a zone and indicate
what RR types are present for an existing
name. NSEC3 differs from NSEC in that it
prevents zone enumeration but is more
computationally expensive on both the server
and the client than NSEC. Described in RFC
5155.
</p>
</td>
</tr>
<tr>
<td>
<p>
NSEC3PARAM
</p>
</td>
<td>
<p>
Used in DNSSECbis to tell the authoritative
server which NSEC3 chains are available to use.
Described in RFC 5155.
</p>
</td>
</tr>
<tr>
<td>
<p>
NULL
</p>
</td>
<td>
<p>
This is an opaque container.
</p>
</td>
</tr>
<tr>
<td>
<p>
NXT
</p>
</td>
<td>
<p>
Used in DNSSEC to securely indicate that
RRs with an owner name in a certain name interval do
not exist in
a zone and indicate what RR types are present for an
existing name.
Used in original DNSSEC; replaced by NSEC in
DNSSECbis.
Described in RFC 2535.
</p>
</td>
</tr>
<tr>
<td>
<p>
OPENPGPKEY
</p>
</td>
<td>
<p>
Used to hold an OPENPGPKEY.
</p>
</td>
</tr>
<tr>
<td>
<p>
PTR
</p>
</td>
<td>
<p>
A pointer to another part of the domain
name space. Described in RFC 1035.
</p>
</td>
</tr>
<tr>
<td>
<p>
PX
</p>
</td>
<td>
<p>
Provides mappings between RFC 822 and X.400
addresses. Described in RFC 2163.
</p>
</td>
</tr>
<tr>
<td>
<p>
RKEY
</p>
</td>
<td>
<p>
Resource key.
</p>
</td>
</tr>
<tr>
<td>
<p>
RP
</p>
</td>
<td>
<p>
Information on persons responsible
for the domain. Experimental. Described in RFC 1183.
</p>
</td>
</tr>
<tr>
<td>
<p>
RRSIG
</p>
</td>
<td>
<p>
Contains DNSSECbis signature data. Described
in RFC 4034.
</p>
</td>
</tr>
<tr>
<td>
<p>
RT
</p>
</td>
<td>
<p>
Route-through binding for hosts that
do not have their own direct wide area network
addresses.
Experimental. Described in RFC 1183.
</p>
</td>
</tr>
<tr>
<td>
<p>
SIG
</p>
</td>
<td>
<p>
Contains DNSSEC signature data. Used in
original DNSSEC; replaced by RRSIG in
DNSSECbis, but still used for SIG(0).
Described in RFCs 2535 and 2931.
</p>
</td>
</tr>
<tr>
<td>
<p>
SINK
</p>
</td>
<td>
<p>
The kitchen sink record.
</p>
</td>
</tr>
<tr>
<td>
<p>
SMIMEA
</p>
</td>
<td>
<p>
The S/MIME Security Certificate Association.
</p>
</td>
</tr>
<tr>
<td>
<p>
SOA
</p>
</td>
<td>
<p>
Identifies the start of a zone of authority.
Described in RFC 1035.
</p>
</td>
</tr>
<tr>
<td>
<p>
SPF
</p>
</td>
<td>
<p>
Contains the Sender Policy Framework information
for a given email domain. Described in RFC 4408.
</p>
</td>
</tr>
<tr>
<td>
<p>
SRV
</p>
</td>
<td>
<p>
Information about well known network
services (replaces WKS). Described in RFC 2782.
</p>
</td>
</tr>
<tr>
<td>
<p>
SSHFP
</p>
</td>
<td>
<p>
Provides a way to securely publish a secure shell key's
fingerprint. Described in RFC 4255.
</p>
</td>
</tr>
<tr>
<td>
<p>
TA
</p>
</td>
<td>
<p>
Trust Anchor. Experimental.
</p>
</td>
</tr>
<tr>
<td>
<p>
TALINK
</p>
</td>
<td>
<p>
Trust Anchor Link. Experimental.
</p>
</td>
</tr>
<tr>
<td>
<p>
TLSA
</p>
</td>
<td>
<p>
Transport Layer Security Certificate Association.
Described in RFC 6698.
</p>
</td>
</tr>
<tr>
<td>
<p>
TXT
</p>
</td>
<td>
<p>
Text records. Described in RFC 1035.
</p>
</td>
</tr>
<tr>
<td>
<p>
UID
</p>
</td>
<td>
<p>
Reserved.
</p>
</td>
</tr>
<tr>
<td>
<p>
UINFO
</p>
</td>
<td>
<p>
Reserved.
</p>
</td>
</tr>
<tr>
<td>
<p>
UNSPEC
</p>
</td>
<td>
<p>
Reserved. Historical.
</p>
</td>
</tr>
<tr>
<td>
<p>
URI
</p>
</td>
<td>
<p>
Holds a URI. Described in RFC 7553.
</p>
</td>
</tr>
<tr>
<td>
<p>
WKS
</p>
</td>
<td>
<p>
Information about which well known
network services, such as SMTP, that a domain
supports. Historical.
</p>
</td>
</tr>
<tr>
<td>
<p>
X25
</p>
</td>
<td>
<p>
Representation of X.25 network addresses.
Experimental. Described in RFC 1183.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
The following <span class="emphasis"><em>classes</em></span> of resource records
are currently valid in the DNS:
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="0.875in" class="1">
<col width="3.625in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p>
IN
</p>
</td>
<td>
<p>
The Internet.
</p>
</td>
</tr>
<tr>
<td>
<p>
CH
</p>
</td>
<td>
<p>
Chaosnet, a LAN protocol created at MIT in the
mid-1970s.
Rarely used for its historical purpose, but reused for
BIND's
built-in server information zones, e.g.,
<code class="literal">version.bind</code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
HS
</p>
</td>
<td>
<p>
Hesiod, an information service
developed by MIT's Project Athena. It is used to share
information
about various systems databases, such as users,
groups, printers
and so on.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
The owner name is often implicit, rather than forming an
integral
part of the RR. For example, many name servers internally form
tree
or hash structures for the name space, and chain RRs off nodes.
The remaining RR parts are the fixed header (type, class, TTL)
which is consistent for all RRs, and a variable part (RDATA)
that
fits the needs of the resource being described.
</p>
<p>
The meaning of the TTL field is a time limit on how long an
RR can be kept in a cache. This limit does not apply to
authoritative
data in zones; it is also timed out, but by the refreshing
policies
for the zone. The TTL is assigned by the administrator for the
zone where the data originates. While short TTLs can be used to
minimize caching, and a zero TTL prohibits caching, the
realities
of Internet performance suggest that these times should be on
the
order of days for the typical host. If a change can be
anticipated,
the TTL can be reduced prior to the change to minimize
inconsistency
during the change, and then increased back to its former value
following
the change.
</p>
<p>
The data in the RDATA section of RRs is carried as a combination
of binary strings and domain names. The domain names are
frequently
used as "pointers" to other data in the DNS.
</p>
</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>
<p>
RRs are represented in binary form in the packets of the DNS
protocol, and are usually represented in highly encoded form
when
stored in a name server or resolver. In the examples provided
in
RFC 1034, a style similar to that used in master files was
employed
in order to show the contents of RRs. In this format, most RRs
are shown on a single line, although continuation lines are
possible
using parentheses.
</p>
<p>
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.
</p>
<p>
Following the owner, we list the TTL, type, and class of the
RR. Class and type use the mnemonics defined above, and TTL is
an integer before the type field. In order to avoid ambiguity
in
parsing, type and class mnemonics are disjoint, TTLs are
integers,
and the type mnemonic is always last. The IN class and TTL
values
are often omitted from examples in the interests of clarity.
</p>
<p>
The resource data or RDATA section of the RR are given using
knowledge of the typical representation for the data.
</p>
<p>
For example, we might show the RRs carried in a message as:
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.381in" class="1">
<col width="1.020in" class="2">
<col width="2.099in" class="3">
</colgroup>
<tbody>
<tr>
<td>
<p>
<code class="literal">ISI.EDU.</code>
</p>
</td>
<td>
<p>
<code class="literal">MX</code>
</p>
</td>
<td>
<p>
<code class="literal">10 VENERA.ISI.EDU.</code>
</p>
</td>
</tr>
<tr>
<td>
<p></p>
</td>
<td>
<p>
<code class="literal">MX</code>
</p>
</td>
<td>
<p>
<code class="literal">10 VAXA.ISI.EDU</code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">VENERA.ISI.EDU</code>
</p>
</td>
<td>
<p>
<code class="literal">A</code>
</p>
</td>
<td>
<p>
<code class="literal">128.9.0.32</code>
</p>
</td>
</tr>
<tr>
<td>
<p></p>
</td>
<td>
<p>
<code class="literal">A</code>
</p>
</td>
<td>
<p>
<code class="literal">10.1.0.52</code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">VAXA.ISI.EDU</code>
</p>
</td>
<td>
<p>
<code class="literal">A</code>
</p>
</td>
<td>
<p>
<code class="literal">10.2.0.27</code>
</p>
</td>
</tr>
<tr>
<td>
<p></p>
</td>
<td>
<p>
<code class="literal">A</code>
</p>
</td>
<td>
<p>
<code class="literal">128.9.0.33</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
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.
</p>
<p>
The above example shows six RRs, with two RRs at each of three
domain names.
</p>
<p>
Similarly we might see:
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.491in" class="1">
<col width="1.067in" class="2">
<col width="2.067in" class="3">
</colgroup>
<tbody>
<tr>
<td>
<p>
<code class="literal">XX.LCS.MIT.EDU.</code>
</p>
</td>
<td>
<p>
<code class="literal">IN A</code>
</p>
</td>
<td>
<p>
<code class="literal">10.0.0.44</code>
</p>
</td>
</tr>
<tr>
<td>�</td>
<td>
<p>
<code class="literal">CH A</code>
</p>
</td>
<td>
<p>
<code class="literal">MIT.EDU. 2420</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
This example shows two addresses for
<code class="literal">XX.LCS.MIT.EDU</code>, each of a different class.
</p>
</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>
<p>
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.
</p>
<p>
MX records are used to control delivery of email. The data
specified in the record is a priority and a domain name. The
priority
controls the order in which email delivery is attempted, with the
lowest number first. If two priorities are the same, a server is
chosen randomly. If no servers at a given priority are responding,
the mail transport agent will fall back to the next largest
priority.
Priority numbers do not have any absolute meaning — they are
relevant
only respective to other MX records for that domain name. The
domain
name given is the machine to which the mail will be delivered.
It <span class="emphasis"><em>must</em></span> have an associated address record
(A or AAAA) — CNAME is not sufficient.
</p>
<p>
For a given domain, if there is both a CNAME record and an
MX record, the MX record is in error, and will be ignored.
Instead,
the mail will be delivered to the server specified in the MX
record
pointed to by the CNAME.
For example:
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.708in" class="1">
<col width="0.444in" class="2">
<col width="0.444in" class="3">
<col width="0.976in" class="4">
<col width="1.553in" class="5">
</colgroup>
<tbody>
<tr>
<td>
<p>
<code class="literal">example.com.</code>
</p>
</td>
<td>
<p>
<code class="literal">IN</code>
</p>
</td>
<td>
<p>
<code class="literal">MX</code>
</p>
</td>
<td>
<p>
<code class="literal">10</code>
</p>
</td>
<td>
<p>
<code class="literal">mail.example.com.</code>
</p>
</td>
</tr>
<tr>
<td>
<p></p>
</td>
<td>
<p>
<code class="literal">IN</code>
</p>
</td>
<td>
<p>
<code class="literal">MX</code>
</p>
</td>
<td>
<p>
<code class="literal">10</code>
</p>
</td>
<td>
<p>
<code class="literal">mail2.example.com.</code>
</p>
</td>
</tr>
<tr>
<td>
<p></p>
</td>
<td>
<p>
<code class="literal">IN</code>
</p>
</td>
<td>
<p>
<code class="literal">MX</code>
</p>
</td>
<td>
<p>
<code class="literal">20</code>
</p>
</td>
<td>
<p>
<code class="literal">mail.backup.org.</code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">mail.example.com.</code>
</p>
</td>
<td>
<p>
<code class="literal">IN</code>
</p>
</td>
<td>
<p>
<code class="literal">A</code>
</p>
</td>
<td>
<p>
<code class="literal">10.0.0.1</code>
</p>
</td>
<td>
<p></p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">mail2.example.com.</code>
</p>
</td>
<td>
<p>
<code class="literal">IN</code>
</p>
</td>
<td>
<p>
<code class="literal">A</code>
</p>
</td>
<td>
<p>
<code class="literal">10.0.0.2</code>
</p>
</td>
<td>
<p></p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
Mail delivery will be attempted to <code class="literal">mail.example.com</code> and
<code class="literal">mail2.example.com</code> (in
any order), and if neither of those succeed, delivery to <code class="literal">mail.backup.org</code> will
be attempted.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="Setting_TTLs"></a>Setting TTLs</h3></div></div></div>
<p>
The time-to-live of the RR field is a 32-bit integer represented
in units of seconds, and is primarily used by resolvers when they
cache RRs. The TTL describes how long a RR can be cached before it
should be discarded. The following three types of TTL are
currently
used in a zone file.
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="0.750in" class="1">
<col width="4.375in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p>
SOA
</p>
</td>
<td>
<p>
The last field in the SOA is the negative
caching TTL. This controls how long other servers will
cache no-such-domain
(NXDOMAIN) responses from you.
</p>
<p>
The maximum time for
negative caching is 3 hours (3h).
</p>
</td>
</tr>
<tr>
<td>
<p>
$TTL
</p>
</td>
<td>
<p>
The $TTL directive at the top of the
zone file (before the SOA) gives a default TTL for every
RR without
a specific TTL set.
</p>
</td>
</tr>
<tr>
<td>
<p>
RR TTLs
</p>
</td>
<td>
<p>
Each RR can have a TTL as the second
field in the RR, which will control how long other
servers can cache it.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
All of these TTLs default to units of seconds, though units
can be explicitly specified, for example, <code class="literal">1h30m</code>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="ipv4_reverse"></a>Inverse Mapping in IPv4</h3></div></div></div>
<p>
Reverse name resolution (that is, translation from IP address
to name) is achieved by means of the <span class="emphasis"><em>in-addr.arpa</em></span> domain
and PTR records. Entries in the in-addr.arpa domain are made in
least-to-most significant order, read left to right. This is the
opposite order to the way IP addresses are usually written. Thus,
a machine with an IP address of 10.1.2.3 would have a
corresponding
in-addr.arpa name of
3.2.1.10.in-addr.arpa. This name should have a PTR resource record
whose data field is the name of the machine or, optionally,
multiple
PTR records if the machine has more than one name. For example,
in the [<span class="optional">example.com</span>] domain:
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.125in" class="1">
<col width="4.000in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p>
<code class="literal">$ORIGIN</code>
</p>
</td>
<td>
<p>
<code class="literal">2.1.10.in-addr.arpa</code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">3</code>
</p>
</td>
<td>
<p>
<code class="literal">IN PTR foo.example.com.</code>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
The <span class="command"><strong>$ORIGIN</strong></span> lines in the examples
are for providing context to the examples only — they do not
necessarily
appear in the actual usage. They are only used here to indicate
that the example is relative to the listed origin.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="zone_directives"></a>Other Zone File Directives</h3></div></div></div>
<p>
The Master File Format was initially defined in RFC 1035 and
has subsequently been extended. While the Master File Format
itself
is class independent all records in a Master File must be of the
same
class.
</p>
<p>
Master File Directives include <span class="command"><strong>$ORIGIN</strong></span>, <span class="command"><strong>$INCLUDE</strong></span>,
and <span class="command"><strong>$TTL.</strong></span>
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="atsign"></a>The <span class="command"><strong>@</strong></span> (at-sign)</h4></div></div></div>
<p>
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
<<code class="varname">zone_name</code>> (followed by
trailing dot).
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="origin_directive"></a>The <span class="command"><strong>$ORIGIN</strong></span> Directive</h4></div></div></div>
<p>
Syntax: <span class="command"><strong>$ORIGIN</strong></span>
<em class="replaceable"><code>domain-name</code></em>
[<span class="optional"><em class="replaceable"><code>comment</code></em></span>]
</p>
<p><span class="command"><strong>$ORIGIN</strong></span>
sets the domain name that will be appended to any
unqualified records. When a zone is first read in there
is an implicit <span class="command"><strong>$ORIGIN</strong></span>
<<code class="varname">zone_name</code>><span class="command"><strong>.</strong></span>
(followed by trailing dot).
The current <span class="command"><strong>$ORIGIN</strong></span> is appended to
the domain specified in the <span class="command"><strong>$ORIGIN</strong></span>
argument if it is not absolute.
</p>
<pre class="programlisting">
$ORIGIN example.com.
WWW CNAME MAIN-SERVER
</pre>
<p>
is equivalent to
</p>
<pre class="programlisting">
WWW.EXAMPLE.COM. CNAME MAIN-SERVER.EXAMPLE.COM.
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="include_directive"></a>The <span class="command"><strong>$INCLUDE</strong></span> Directive</h4></div></div></div>
<p>
Syntax: <span class="command"><strong>$INCLUDE</strong></span>
<em class="replaceable"><code>filename</code></em>
[<span class="optional">
<em class="replaceable"><code>origin</code></em> </span>]
[<span class="optional"> <em class="replaceable"><code>comment</code></em> </span>]
</p>
<p>
Read and process the file <code class="filename">filename</code> as
if it were included into the file at this point. If <span class="command"><strong>origin</strong></span> is
specified the file is processed with <span class="command"><strong>$ORIGIN</strong></span> set
to that value, otherwise the current <span class="command"><strong>$ORIGIN</strong></span> is
used.
</p>
<p>
The origin and the current domain name
revert to the values they had prior to the <span class="command"><strong>$INCLUDE</strong></span> once
the file has been read.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
RFC 1035 specifies that the current origin should be restored
after
an <span class="command"><strong>$INCLUDE</strong></span>, but it is silent
on whether the current
domain name should also be restored. BIND 9 restores both of
them.
This could be construed as a deviation from RFC 1035, a
feature, or both.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="ttl_directive"></a>The <span class="command"><strong>$TTL</strong></span> Directive</h4></div></div></div>
<p>
Syntax: <span class="command"><strong>$TTL</strong></span>
<em class="replaceable"><code>default-ttl</code></em>
[<span class="optional">
<em class="replaceable"><code>comment</code></em> </span>]
</p>
<p>
Set the default Time To Live (TTL) for subsequent records
with undefined TTLs. Valid TTLs are of the range 0-2147483647
seconds.
</p>
<p><span class="command"><strong>$TTL</strong></span>
is defined in RFC 2308.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="generate_directive"></a><acronym class="acronym">BIND</acronym> Master File Extension: the <span class="command"><strong>$GENERATE</strong></span> Directive</h3></div></div></div>
<p>
Syntax: <span class="command"><strong>$GENERATE</strong></span>
<em class="replaceable"><code>range</code></em>
<em class="replaceable"><code>lhs</code></em>
[<span class="optional"><em class="replaceable"><code>ttl</code></em></span>]
[<span class="optional"><em class="replaceable"><code>class</code></em></span>]
<em class="replaceable"><code>type</code></em>
<em class="replaceable"><code>rhs</code></em>
[<span class="optional"><em class="replaceable"><code>comment</code></em></span>]
</p>
<p><span class="command"><strong>$GENERATE</strong></span>
is used to create a series of resource records that only
differ from each other by an
iterator. <span class="command"><strong>$GENERATE</strong></span> 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.
</p>
<pre class="programlisting">$ORIGIN 0.0.192.IN-ADDR.ARPA.
$GENERATE 1-2 @ NS SERVER$.EXAMPLE.
$GENERATE 1-127 $ CNAME $.0</pre>
<p>
is equivalent to
</p>
<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>
<p>
Generate a set of A and MX records. Note the MX's right hand
side is a quoted string. The quotes will be stripped when the
right hand side is processed.
</p>
<pre class="programlisting">
$ORIGIN EXAMPLE.
$GENERATE 1-127 HOST-$ A 1.2.3.$
$GENERATE 1-127 HOST-$ MX "0 ."</pre>
<p>
is equivalent to
</p>
<pre class="programlisting">HOST-1.EXAMPLE. A 1.2.3.1
HOST-1.EXAMPLE. MX 0 .
HOST-2.EXAMPLE. A 1.2.3.2
HOST-2.EXAMPLE. MX 0 .
HOST-3.EXAMPLE. A 1.2.3.3
HOST-3.EXAMPLE. MX 0 .
...
HOST-127.EXAMPLE. A 1.2.3.127
HOST-127.EXAMPLE. MX 0 .
</pre>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="0.875in" class="1">
<col width="4.250in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p><span class="command"><strong>range</strong></span></p>
</td>
<td>
<p>
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.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>lhs</strong></span></p>
</td>
<td>
<p>This
describes the owner name of the resource records
to be created. Any single <span class="command"><strong>$</strong></span>
(dollar sign)
symbols within the <span class="command"><strong>lhs</strong></span> string
are replaced by the iterator value.
To get a $ in the output, you need to escape the
<span class="command"><strong>$</strong></span> using a backslash
<span class="command"><strong>\</strong></span>,
e.g. <span class="command"><strong>\$</strong></span>. The
<span class="command"><strong>$</strong></span> may optionally be followed
by modifiers which change the offset from the
iterator, field width and base.
Modifiers are introduced by a
<span class="command"><strong>{</strong></span> (left brace) immediately following the
<span class="command"><strong>$</strong></span> as
<span class="command"><strong>${offset[,width[,base]]}</strong></span>.
For example, <span class="command"><strong>${-20,3,d}</strong></span>
subtracts 20 from the current value, prints the
result as a decimal in a zero-padded field of
width 3.
Available output forms are decimal
(<span class="command"><strong>d</strong></span>), octal
(<span class="command"><strong>o</strong></span>), hexadecimal
(<span class="command"><strong>x</strong></span> or <span class="command"><strong>X</strong></span>
for uppercase) and nibble
(<span class="command"><strong>n</strong></span> or <span class="command"><strong>N</strong></span>\
for uppercase). The default modifier is
<span class="command"><strong>${0,0,d}</strong></span>. If the
<span class="command"><strong>lhs</strong></span> is not absolute, the
current <span class="command"><strong>$ORIGIN</strong></span> is appended
to the name.
</p>
<p>
In nibble mode the value will be treated as
if it was a reversed hexadecimal string
with each hexadecimal digit as a separate
label. The width field includes the label
separator.
</p>
<p>
For compatibility with earlier versions,
<span class="command"><strong>$$</strong></span> is still recognized as
indicating a literal $ in the output.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>ttl</strong></span></p>
</td>
<td>
<p>
Specifies the time-to-live of the generated records. If
not specified this will be inherited using the
normal TTL inheritance rules.
</p>
<p><span class="command"><strong>class</strong></span>
and <span class="command"><strong>ttl</strong></span> can be
entered in either order.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>class</strong></span></p>
</td>
<td>
<p>
Specifies the class of the generated records.
This must match the zone class if it is
specified.
</p>
<p><span class="command"><strong>class</strong></span>
and <span class="command"><strong>ttl</strong></span> can be
entered in either order.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>type</strong></span></p>
</td>
<td>
<p>
Any valid type.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>rhs</strong></span></p>
</td>
<td>
<p>
<span class="command"><strong>rhs</strong></span>, optionally, quoted string.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
The <span class="command"><strong>$GENERATE</strong></span> directive is a <acronym class="acronym">BIND</acronym> extension
and not part of the standard zone file format.
</p>
<p>
BIND 8 did not support the optional TTL and CLASS fields.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="zonefile_format"></a>Additional File Formats</h3></div></div></div>
<p>
In addition to the standard textual format, BIND 9
supports the ability to read or dump to zone files in
other formats.
</p>
<p>
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.
</p>
<p>
An even faster alternative is the <code class="constant">map</code>
format, which is an image of a <acronym class="acronym">BIND</acronym> 9
in-memory zone database; it is capable of being loaded
directly into memory via the <span class="command"><strong>mmap()</strong></span>
function; the zone can begin serving queries almost
immediately.
</p>
<p>
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 <span class="command"><strong>named-compilezone</strong></span> command.
For a secondary server or for a dynamic zone, it is automatically
generated (if this format is specified by the
<span class="command"><strong>masterfile-format</strong></span> option) when
<span class="command"><strong>named</strong></span> dumps the zone contents after
zone transfer or when applying prior updates.
</p>
<p>
If a zone file in a binary format needs manual modification,
it first must be converted to a textual form by the
<span class="command"><strong>named-compilezone</strong></span> command. All
necessary modification should go to the text file, which
should then be converted to the binary form by the
<span class="command"><strong>named-compilezone</strong></span> command again.
</p>
<p>
Note that <span class="command"><strong>map</strong></span> format is extremely
architecture-specific. A <code class="constant">map</code>
file <span class="emphasis"><em>cannot</em></span> 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.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="statistics"></a>BIND9 Statistics</h2></div></div></div>
<p>
<acronym class="acronym">BIND</acronym> 9 maintains lots of statistics
information and provides several interfaces for users to
get access to the statistics.
The available statistics include all statistics counters
that were available in <acronym class="acronym">BIND</acronym> 8 and
are meaningful in <acronym class="acronym">BIND</acronym> 9,
and other information that is considered useful.
</p>
<p>
The statistics information is categorized into the following
sections.
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="3.300in" class="1">
<col width="2.625in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p>Incoming Requests</p>
</td>
<td>
<p>
The number of incoming DNS requests for each OPCODE.
</p>
</td>
</tr>
<tr>
<td>
<p>Incoming Queries</p>
</td>
<td>
<p>
The number of incoming queries for each RR type.
</p>
</td>
</tr>
<tr>
<td>
<p>Outgoing Queries</p>
</td>
<td>
<p>
The number of outgoing queries for each RR
type sent from the internal resolver.
Maintained per view.
</p>
</td>
</tr>
<tr>
<td>
<p>Name Server Statistics</p>
</td>
<td>
<p>
Statistics counters about incoming request processing.
</p>
</td>
</tr>
<tr>
<td>
<p>Zone Maintenance Statistics</p>
</td>
<td>
<p>
Statistics counters regarding zone maintenance
operations such as zone transfers.
</p>
</td>
</tr>
<tr>
<td>
<p>Resolver Statistics</p>
</td>
<td>
<p>
Statistics counters about name resolution
performed in the internal resolver.
Maintained per view.
</p>
</td>
</tr>
<tr>
<td>
<p>Cache DB RRsets</p>
</td>
<td>
<p>
The number of RRsets per RR type and nonexistent
names stored in the cache database.
If the exclamation mark (!) is printed for a RR
type, it means that particular type of RRset is
known to be nonexistent (this is also known as
"NXRRSET"). If a hash mark (#) is present then
the RRset is marked for garbage collection.
Maintained per view.
</p>
</td>
</tr>
<tr>
<td>
<p>Socket I/O Statistics</p>
</td>
<td>
<p>
Statistics counters about network related events.
</p>
</td>
</tr>
</tbody>
</table>
</div>
<p>
A subset of Name Server Statistics is collected and shown
per zone for which the server has the authority when
<span class="command"><strong>zone-statistics</strong></span> is set to
<strong class="userinput"><code>full</code></strong> (or <strong class="userinput"><code>yes</code></strong>
for backward compatibility. See the description of
<span class="command"><strong>zone-statistics</strong></span> in <a class="xref" href="Bv9ARM.ch06.html#options" title="options Statement Definition and Usage">the section called “<span class="command"><strong>options</strong></span> Statement Definition and
Usage”</a>
for further details.
</p>
<p>
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.</p>
<p>
There are currently two user interfaces to get access to the
statistics.
One is in the plain text format dumped to the file specified
by the <span class="command"><strong>statistics-file</strong></span> configuration option.
The other is remotely accessible via a statistics channel
when the <span class="command"><strong>statistics-channels</strong></span> statement
is specified in the configuration file
(see <a class="xref" href="Bv9ARM.ch06.html#statschannels" title="statistics-channels Statement Grammar">the section called “<span class="command"><strong>statistics-channels</strong></span> Statement Grammar”</a>.)
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="statsfile"></a>The Statistics File</h3></div></div></div>
<p>
The text format statistics dump begins with a line, like:
</p>
<p>
<span class="command"><strong>+++ Statistics Dump +++ (973798949)</strong></span>
</p>
<p>
The number in parentheses is a standard
Unix-style timestamp, measured as seconds since January 1, 1970.
Following
that line is a set of statistics information, which is categorized
as described above.
Each section begins with a line, like:
</p>
<p>
<span class="command"><strong>++ Name Server Statistics ++</strong></span>
</p>
<p>
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.
</p>
<p>
The statistics dump ends with the line where the
number is identical to the number in the beginning line; for example:
</p>
<p>
<span class="command"><strong>--- Statistics Dump --- (973798949)</strong></span>
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="statistics_counters"></a>Statistics Counters</h3></div></div></div>
<p>
The following tables summarize statistics counters that
<acronym class="acronym">BIND</acronym> 9 provides.
For each row of the tables, the leftmost column is the
abbreviated symbol name of that counter.
These symbols are shown in the statistics information
accessed via an HTTP statistics channel.
The rightmost column gives the description of the counter,
which is also shown in the statistics file
(but, in this document, possibly with slight modification
for better readability).
Additional notes may also be provided in this column.
When a middle column exists between these two columns,
it gives the corresponding counter name of the
<acronym class="acronym">BIND</acronym> 8 statistics, if applicable.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="stats_counters"></a>Name Server Statistics Counters</h4></div></div></div>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.150in" class="1">
<col width="1.150in" class="2">
<col width="3.350in" class="3">
</colgroup>
<tbody>
<tr>
<td>
<p>
<span class="emphasis"><em>Symbol</em></span>
</p>
</td>
<td>
<p>
<span class="emphasis"><em>BIND8 Symbol</em></span>
</p>
</td>
<td>
<p>
<span class="emphasis"><em>Description</em></span>
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>Requestv4</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RQ</strong></span></p>
</td>
<td>
<p>
IPv4 requests received.
Note: this also counts non query requests.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>Requestv6</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RQ</strong></span></p>
</td>
<td>
<p>
IPv6 requests received.
Note: this also counts non query requests.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>ReqEdns0</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Requests with EDNS(0) received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>ReqBadEDNSVer</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Requests with unsupported EDNS version received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>ReqTSIG</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Requests with TSIG received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>ReqSIG0</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Requests with SIG(0) received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>ReqBadSIG</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Requests with invalid (TSIG or SIG(0)) signature.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>ReqTCP</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RTCP</strong></span></p>
</td>
<td>
<p>
TCP requests received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>AuthQryRej</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RUQ</strong></span></p>
</td>
<td>
<p>
Authoritative (non recursive) queries rejected.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>RecQryRej</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RURQ</strong></span></p>
</td>
<td>
<p>
Recursive queries rejected.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>XfrRej</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RUXFR</strong></span></p>
</td>
<td>
<p>
Zone transfer requests rejected.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>UpdateRej</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RUUpd</strong></span></p>
</td>
<td>
<p>
Dynamic update requests rejected.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>Response</strong></span></p>
</td>
<td>
<p><span class="command"><strong>SAns</strong></span></p>
</td>
<td>
<p>
Responses sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>RespTruncated</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Truncated responses sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>RespEDNS0</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Responses with EDNS(0) sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>RespTSIG</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Responses with TSIG sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>RespSIG0</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Responses with SIG(0) sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QrySuccess</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Queries resulted in a successful answer.
This means the query which returns a NOERROR response
with at least one answer RR.
This corresponds to the
<span class="command"><strong>success</strong></span> counter
of previous versions of
<acronym class="acronym">BIND</acronym> 9.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryAuthAns</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Queries resulted in authoritative answer.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryNoauthAns</strong></span></p>
</td>
<td>
<p><span class="command"><strong>SNaAns</strong></span></p>
</td>
<td>
<p>
Queries resulted in non authoritative answer.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryReferral</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Queries resulted in referral answer.
This corresponds to the
<span class="command"><strong>referral</strong></span> counter
of previous versions of
<acronym class="acronym">BIND</acronym> 9.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryNxrrset</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Queries resulted in NOERROR responses with no data.
This corresponds to the
<span class="command"><strong>nxrrset</strong></span> counter
of previous versions of
<acronym class="acronym">BIND</acronym> 9.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QrySERVFAIL</strong></span></p>
</td>
<td>
<p><span class="command"><strong>SFail</strong></span></p>
</td>
<td>
<p>
Queries resulted in SERVFAIL.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryFORMERR</strong></span></p>
</td>
<td>
<p><span class="command"><strong>SFErr</strong></span></p>
</td>
<td>
<p>
Queries resulted in FORMERR.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryNXDOMAIN</strong></span></p>
</td>
<td>
<p><span class="command"><strong>SNXD</strong></span></p>
</td>
<td>
<p>
Queries resulted in NXDOMAIN.
This corresponds to the
<span class="command"><strong>nxdomain</strong></span> counter
of previous versions of
<acronym class="acronym">BIND</acronym> 9.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryRecursion</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RFwdQ</strong></span></p>
</td>
<td>
<p>
Queries which caused the server
to perform recursion in order to find the final answer.
This corresponds to the
<span class="command"><strong>recursion</strong></span> counter
of previous versions of
<acronym class="acronym">BIND</acronym> 9.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryDuplicate</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RDupQ</strong></span></p>
</td>
<td>
<p>
Queries which the server attempted to
recurse but discovered an existing query with the same
IP address, port, query ID, name, type and class
already being processed.
This corresponds to the
<span class="command"><strong>duplicate</strong></span> counter
of previous versions of
<acronym class="acronym">BIND</acronym> 9.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryDropped</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Recursive queries for which the server
discovered an excessive number of existing
recursive queries for the same name, type and
class and were subsequently dropped.
This is the number of dropped queries due to
the reason explained with the
<span class="command"><strong>clients-per-query</strong></span>
and
<span class="command"><strong>max-clients-per-query</strong></span>
options
(see the description about
<a class="xref" href="Bv9ARM.ch06.html#clients-per-query"><span class="command"><strong>clients-per-query</strong></span></a>.)
This corresponds to the
<span class="command"><strong>dropped</strong></span> counter
of previous versions of
<acronym class="acronym">BIND</acronym> 9.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryFailure</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Other query failures.
This corresponds to the
<span class="command"><strong>failure</strong></span> counter
of previous versions of
<acronym class="acronym">BIND</acronym> 9.
Note: this counter is provided mainly for
backward compatibility with the previous versions.
Normally a more fine-grained counters such as
<span class="command"><strong>AuthQryRej</strong></span> and
<span class="command"><strong>RecQryRej</strong></span>
that would also fall into this counter are provided,
and so this counter would not be of much
interest in practice.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryNXRedir</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Queries resulted in NXDOMAIN that were redirected.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryNXRedirRLookup</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Queries resulted in NXDOMAIN that were redirected
and resulted in a successful remote lookup.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>XfrReqDone</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Requested zone transfers completed.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>UpdateReqFwd</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Update requests forwarded.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>UpdateRespFwd</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Update responses forwarded.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>UpdateFwdFail</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Dynamic update forward failed.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>UpdateDone</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Dynamic updates completed.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>UpdateFail</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Dynamic updates failed.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>UpdateBadPrereq</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Dynamic updates rejected due to prerequisite failure.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>RateDropped</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Responses dropped by rate limits.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>RateSlipped</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Responses truncated by rate limits.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>RPZRewrites</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Response policy zone rewrites.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="zone_stats"></a>Zone Maintenance Statistics Counters</h4></div></div></div>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.150in" class="1">
<col width="3.350in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p>
<span class="emphasis"><em>Symbol</em></span>
</p>
</td>
<td>
<p>
<span class="emphasis"><em>Description</em></span>
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>NotifyOutv4</strong></span></p>
</td>
<td>
<p>
IPv4 notifies sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>NotifyOutv6</strong></span></p>
</td>
<td>
<p>
IPv6 notifies sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>NotifyInv4</strong></span></p>
</td>
<td>
<p>
IPv4 notifies received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>NotifyInv6</strong></span></p>
</td>
<td>
<p>
IPv6 notifies received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>NotifyRej</strong></span></p>
</td>
<td>
<p>
Incoming notifies rejected.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>SOAOutv4</strong></span></p>
</td>
<td>
<p>
IPv4 SOA queries sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>SOAOutv6</strong></span></p>
</td>
<td>
<p>
IPv6 SOA queries sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>AXFRReqv4</strong></span></p>
</td>
<td>
<p>
IPv4 AXFR requested.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>AXFRReqv6</strong></span></p>
</td>
<td>
<p>
IPv6 AXFR requested.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>IXFRReqv4</strong></span></p>
</td>
<td>
<p>
IPv4 IXFR requested.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>IXFRReqv6</strong></span></p>
</td>
<td>
<p>
IPv6 IXFR requested.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>XfrSuccess</strong></span></p>
</td>
<td>
<p>
Zone transfer requests succeeded.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>XfrFail</strong></span></p>
</td>
<td>
<p>
Zone transfer requests failed.
</p>
</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 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>
<p>
<span class="emphasis"><em>Symbol</em></span>
</p>
</td>
<td>
<p>
<span class="emphasis"><em>BIND8 Symbol</em></span>
</p>
</td>
<td>
<p>
<span class="emphasis"><em>Description</em></span>
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>Queryv4</strong></span></p>
</td>
<td>
<p><span class="command"><strong>SFwdQ</strong></span></p>
</td>
<td>
<p>
IPv4 queries sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>Queryv6</strong></span></p>
</td>
<td>
<p><span class="command"><strong>SFwdQ</strong></span></p>
</td>
<td>
<p>
IPv6 queries sent.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>Responsev4</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RR</strong></span></p>
</td>
<td>
<p>
IPv4 responses received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>Responsev6</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RR</strong></span></p>
</td>
<td>
<p>
IPv6 responses received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>NXDOMAIN</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RNXD</strong></span></p>
</td>
<td>
<p>
NXDOMAIN received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>SERVFAIL</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RFail</strong></span></p>
</td>
<td>
<p>
SERVFAIL received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>FORMERR</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RFErr</strong></span></p>
</td>
<td>
<p>
FORMERR received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>OtherError</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RErr</strong></span></p>
</td>
<td>
<p>
Other errors received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>EDNS0Fail</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
EDNS(0) query failures.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>Mismatch</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RDupR</strong></span></p>
</td>
<td>
<p>
Mismatch responses received.
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 <span class="command"><strong>port</strong></span> option.)
This may be an indication of a cache
poisoning attempt.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>Truncated</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Truncated responses received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>Lame</strong></span></p>
</td>
<td>
<p><span class="command"><strong>RLame</strong></span></p>
</td>
<td>
<p>
Lame delegations received.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>Retry</strong></span></p>
</td>
<td>
<p><span class="command"><strong>SDupQ</strong></span></p>
</td>
<td>
<p>
Query retries performed.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QueryAbort</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Queries aborted due to quota control.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QuerySockFail</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Failures in opening query sockets.
One common reason for such failures is a
failure of opening a new socket due to a
limitation on file descriptors.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QueryTimeout</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Query timeouts.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>GlueFetchv4</strong></span></p>
</td>
<td>
<p><span class="command"><strong>SSysQ</strong></span></p>
</td>
<td>
<p>
IPv4 NS address fetches invoked.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>GlueFetchv6</strong></span></p>
</td>
<td>
<p><span class="command"><strong>SSysQ</strong></span></p>
</td>
<td>
<p>
IPv6 NS address fetches invoked.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>GlueFetchv4Fail</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
IPv4 NS address fetch failed.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>GlueFetchv6Fail</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
IPv6 NS address fetch failed.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>ValAttempt</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
DNSSEC validation attempted.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>ValOk</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
DNSSEC validation succeeded.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>ValNegOk</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
DNSSEC validation on negative information succeeded.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>ValFail</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
DNSSEC validation failed.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>QryRTTnn</strong></span></p>
</td>
<td>
<p><span class="command"><strong></strong></span></p>
</td>
<td>
<p>
Frequency table on round trip times (RTTs) of
queries.
Each <span class="command"><strong>nn</strong></span> specifies the corresponding
frequency.
In the sequence of
<span class="command"><strong>nn_1</strong></span>,
<span class="command"><strong>nn_2</strong></span>,
...,
<span class="command"><strong>nn_m</strong></span>,
the value of <span class="command"><strong>nn_i</strong></span> is the
number of queries whose RTTs are between
<span class="command"><strong>nn_(i-1)</strong></span> (inclusive) and
<span class="command"><strong>nn_i</strong></span> (exclusive) milliseconds.
For the sake of convenience we define
<span class="command"><strong>nn_0</strong></span> to be 0.
The last entry should be represented as
<span class="command"><strong>nn_m+</strong></span>, which means the
number of queries whose RTTs are equal to or over
<span class="command"><strong>nn_m</strong></span> milliseconds.
</p>
</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>
<p>
Socket I/O statistics counters are defined per socket
types, which are
<span class="command"><strong>UDP4</strong></span> (UDP/IPv4),
<span class="command"><strong>UDP6</strong></span> (UDP/IPv6),
<span class="command"><strong>TCP4</strong></span> (TCP/IPv4),
<span class="command"><strong>TCP6</strong></span> (TCP/IPv6),
<span class="command"><strong>Unix</strong></span> (Unix Domain), and
<span class="command"><strong>FDwatch</strong></span> (sockets opened outside the
socket module).
In the following table <span class="command"><strong><TYPE></strong></span>
represents a socket type.
Not all counters are available for all socket types;
exceptions are noted in the description field.
</p>
<div class="informaltable">
<table border="1">
<colgroup>
<col width="1.150in" class="1">
<col width="3.350in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p>
<span class="emphasis"><em>Symbol</em></span>
</p>
</td>
<td>
<p>
<span class="emphasis"><em>Description</em></span>
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong><TYPE>Open</strong></span></p>
</td>
<td>
<p>
Sockets opened successfully.
This counter is not applicable to the
<span class="command"><strong>FDwatch</strong></span> type.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong><TYPE>OpenFail</strong></span></p>
</td>
<td>
<p>
Failures of opening sockets.
This counter is not applicable to the
<span class="command"><strong>FDwatch</strong></span> type.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong><TYPE>Close</strong></span></p>
</td>
<td>
<p>
Sockets closed.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong><TYPE>BindFail</strong></span></p>
</td>
<td>
<p>
Failures of binding sockets.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong><TYPE>ConnFail</strong></span></p>
</td>
<td>
<p>
Failures of connecting sockets.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong><TYPE>Conn</strong></span></p>
</td>
<td>
<p>
Connections established successfully.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong><TYPE>AcceptFail</strong></span></p>
</td>
<td>
<p>
Failures of accepting incoming connection requests.
This counter is not applicable to the
<span class="command"><strong>UDP</strong></span> and
<span class="command"><strong>FDwatch</strong></span> types.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong><TYPE>Accept</strong></span></p>
</td>
<td>
<p>
Incoming connections successfully accepted.
This counter is not applicable to the
<span class="command"><strong>UDP</strong></span> and
<span class="command"><strong>FDwatch</strong></span> types.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong><TYPE>SendErr</strong></span></p>
</td>
<td>
<p>
Errors in socket send operations.
This counter corresponds
to <span class="command"><strong>SErr</strong></span> counter of
<span class="command"><strong>BIND</strong></span> 8.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong><TYPE>RecvErr</strong></span></p>
</td>
<td>
<p>
Errors in socket receive operations.
This includes errors of send operations on a
connected UDP socket notified by an ICMP error
message.
</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="bind8_compatibility"></a>Compatibility with <span class="emphasis"><em>BIND</em></span> 8 Counters</h4></div></div></div>
<p>
Most statistics counters that were available
in <span class="command"><strong>BIND</strong></span> 8 are also supported in
<span class="command"><strong>BIND</strong></span> 9 as shown in the above tables.
Here are notes about other counters that do not appear
in these tables.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><span class="command"><strong>RFwdR,SFwdR</strong></span></span></dt>
<dd>
<p>
These counters are not supported
because <span class="command"><strong>BIND</strong></span> 9 does not adopt
the notion of <span class="emphasis"><em>forwarding</em></span>
as <span class="command"><strong>BIND</strong></span> 8 did.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>RAXFR</strong></span></span></dt>
<dd>
<p>
This counter is accessible in the Incoming Queries section.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>RIQ</strong></span></span></dt>
<dd>
<p>
This counter is accessible in the Incoming Requests section.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>ROpts</strong></span></span></dt>
<dd>
<p>
This counter is not supported
because <span class="command"><strong>BIND</strong></span> 9 does not care
about IP options in the first place.
</p>
</dd>
</dl></div>
</div>
</div>
</div>
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