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<H2>BIND Configuration File Guide -- <CODE>options</CODE> Statement</H2>

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<A NAME="Syntax"><H3>Syntax</H3></A>

<PRE>
options {
  [ directory <VAR>path_name</VAR>; ]
  [ named-xfer <VAR>path_name</VAR>; ]
  [ dump-file <VAR>path_name</VAR>; ]
  [ memstatistics-file <VAR>path_name</VAR>; ]
  [ pid-file <VAR>path_name</VAR>; ]
  [ statistics-file <VAR>path_name</VAR>; ]
  [ auth-nxdomain <VAR><A HREF="docdef.html">yes_or_no</A></VAR>; ]
  [ deallocate-on-exit <VAR><A HREF="docdef.html">yes_or_no</A></VAR>; ]
  [ fake-iquery <VAR><A HREF="docdef.html">yes_or_no</A></VAR>; ]
  [ fetch-glue <VAR><A HREF="docdef.html">yes_or_no</A></VAR>; ]
  [ multiple-cnames <VAR><A HREF="docdef.html">yes_or_no</A></VAR>; ]
  [ notify <VAR><A HREF="docdef.html">yes_or_no</A></VAR>; ]
  [ recursion <VAR><A HREF="docdef.html">yes_or_no</A></VAR>; ]
  [ forward ( only | first ); ]
  [ forwarders { [ <VAR><A HREF="docdef.html">in_addr</A></VAR> ; [ <VAR><A HREF="docdef.html">in_addr</A></VAR> ; ... ] ] }; ]
  [ check-names ( master | slave | response ) ( warn | fail | ignore); ]
  [ allow-query { <VAR>address_match_list</VAR> }; ]
  [ allow-transfer { <VAR>address_match_list</VAR> }; ]
  [ listen-on [ port <VAR><A HREF="docdef.html">ip_port</A></VAR> ] { <VAR>address_match_list</VAR> }; ]
  [ query-source [ address ( <VAR><A HREF="docdef.html">ip_addr</A></VAR> | * ) ] [ port ( <VAR><A HREF="docdef.html">ip_port</A></VAR> | * ) ] ; ]
  [ max-transfer-time-in <VAR>number</VAR>; ]
  [ transfer-format ( one-answer | many-answers ); ]
  [ transfers-in  <VAR>number</VAR>; ]
  [ transfers-out <VAR>number</VAR>; ]
  [ transfers-per-ns <VAR>number</VAR>; ]
  [ coresize <VAR><A HREF="docdef.html">size_spec</A></VAR> ; ]
  [ datasize <VAR><A HREF="docdef.html">size_spec</A></VAR> ; ]
  [ files <VAR><A HREF="docdef.html">size_spec</A></VAR> ; ]
  [ stacksize <VAR><A HREF="docdef.html">size_spec</A></VAR> ; ]
  [ cleaning-interval <VAR>number</VAR>; ]
  [ interface-interval <VAR>number</VAR>; ]
  [ statistics-interval <VAR>number</VAR>; ]
  [ topology { <VAR>address_match_list</VAR> }; ]
};
</PRE>
<HR>

<A NAME="Usage"><H3>Definition and Use</H3></A>

<P>The options statement sets up global options to be used by
BIND. This statement may appear at only once in a
configuration file; if more than one occurrence is found, the
first occurrence determines the actual options used,
and a warning will be generated.  If there is no options statement,
an options block with each option set to its default will be used.</P>

<H4>Pathnames</H4>

<DL>
<DT><CODE>directory</CODE>
<DD>
The working directory of the server.  Any non-absolute
pathnames in the configuration file will be taken as relative to this
directory.  The default location for most server output files
(e.g. "named.run") is this directory.  If a directory is not
specified, the working directory defaults to ".", the directory from which the
server was started.  The directory specified should be an absolute path.

<DT><CODE>named-xfer</CODE>
<DD>
The pathname to the named-xfer program that the server uses for
inbound zone transfers.  If not specified, the default is
system dependent (e.g.  "/usr/sbin/named-xfer").

<DT><CODE>dump-file</CODE>
<DD>
The pathname of the file the server dumps the database to when it
receives <CODE>SIGINT</CODE> signal (<CODE>ndc dumpdb</CODE>).  If not
specified, the default is "named_dump.db".

<DT><CODE>memstatistics-file</CODE>
<DD>
The pathname of the file the server writes memory usage statistics to on exit,
if <CODE>deallocate-on-exit</CODE> is <CODE>yes</CODE>.  If not
specified, the default is "named.memstats".

<DT><CODE>pid-file</CODE>
<DD>
The pathname of the file the server writes its process ID in.  If not
specified, the default is operating system dependent, but is usually
"/var/run/named.pid" or "/etc/named.pid".  The pid-file is used by
programs like "ndc" that want to send signals to the running
nameserver.

<DT><CODE>statistics-file</CODE>
<DD>
The pathname of the file the server appends statistics to when it
receives <CODE>SIGILL</CODE> signal (<CODE>ndc stats</CODE>).  If not
specified, the default is "named.stats".
</DL>

<A name="BooleanOptions"><H4>Boolean Options</H4></A>

<DL>
<DT><CODE>auth-nxdomain</CODE>
<DD>
If <CODE>yes</CODE>, then the <CODE>AA</CODE> bit is always set on
NXDOMAIN responses, even if the server is not actually authoritative.
The default is <CODE>yes</CODE>.  Do not turn off
<CODE>auth-nxdomain</CODE> unless you are sure you know what you are
doing, as some older software won't like it.

<DT><CODE>deallocate-on-exit</CODE>
<DD>
If <CODE>yes</CODE>, then when the server exits it will painstakingly
deallocate every object it allocated, and then write a memory usage report to
the <CODE>memstatistics-file</CODE>.  The default is <CODE>no</CODE>, because
it is faster to let the operating system clean up.
<CODE>deallocate-on-exit</CODE> is handy for detecting memory leaks.

<DT><CODE>fake-iquery</CODE>
<DD>
If <CODE>yes</CODE>, the server will simulate the obsolete DNS query type
IQUERY.  The default is <CODE>no</CODE>.

<DT><CODE>fetch-glue</CODE>
<DD>
If <CODE>yes</CODE> (the default), the server will fetch "glue" resource
records it doesn't have when constructing the additional data section of
a response.  <CODE>fetch-glue no</CODE> can be used in conjunction with
<CODE>recursion no</CODE> to prevent the server's cache from growing or
becoming corrupted (at the cost of requiring more work from the client).

<DT><CODE>multiple-cnames</CODE>
<DD>
If <CODE>yes</CODE>, then multiple CNAME resource records will be
allowed for a domain name.  The default is <CODE>no</CODE>.  Allowing
multiple CNAME records is against standards and is not recommended.
Multiple CNAME support is available because previous versions of BIND
allowed multiple CNAME records, and these records have been used for load
balancing by a number of sites.

<DT><CODE>notify</CODE>
<DD>
If <CODE>yes</CODE> (the default), DNS NOTIFY messages are sent when a
zone the server is authoritative for changes.  The use of NOTIFY
speeds convergence between the master and its slaves.  Slave servers
that receive a NOTIFY message and understand it will contact the
master server for the zone and see if they need to do a zone transfer, and
if they do, they will initiate it immediately.  The <CODE>notify</CODE>
option may also be specified in the <CODE>zone</CODE> statement, in which
case it overrides the <CODE>options notify</CODE> statement.

<DT><CODE>recursion</CODE>
<DD>
If <CODE>yes</CODE>, and a DNS query requests recursion, then the
server will attempt to do all the work required to answer the query.
If recursion is not on, the server will return a referral to the
client if it doesn't know the answer.  The default is <CODE>yes</CODE>.
See also <CODE>fetch-glue</CODE> above.
</DL>

<H4>Forwarding</H4>

<P>The forwarding facility can be used to create a large sitewide
cache on a few servers, reducing traffic over links to external
nameservers.  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.

<DL>
<DT><CODE>forward</CODE>
<DD>
This option is only meaningful if the <CODE>forwarders</CODE> list is
not empty.  A value of <CODE>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>only</CODE> is specified, the server will only query the
forwarders. 

<DT><CODE>forwarders</CODE>
<DD>
Specifies the IP addresses to be used for forwarding.  The default is the
empty list (no forwarding).
</DL>

<P>Future versions of BIND 8 will provide a more powerful forwarding
system.  The syntax described above will continue to be supported.

<a name="NameChecking"><H4>Name Checking</H4></a>

<P>The server can check domain names based upon their expected client contexts.
For example, a domain name used as a hostname can be checked for compliance
with the RFCs defining valid hostnames.

<P>Three checking methods are available:

<DL>
<DT><CODE>ignore</CODE>
<DD>
No checking is done.

<DT><CODE>warn</CODE>
<DD>
Names are checked against their expected client contexts.  Invalid names are
logged, but processing continues normally.

<DT><CODE>fail</CODE>
<DD>
Names are checked against their expected client contexts.  Invalid names are
logged, and the offending data is rejected.
</DL>

<P>The server can check names three areas: master zone files, slave
zone files, and in responses to queries the server has initiated.  If
<CODE>check-names response fail</CODE> has been specified, and
answering the client's question would require sending an invalid name
to the client, the server will send a REFUSED response code to the
client.

<P>The defaults are:

<PRE>
    check-names master fail;
    check-names slave warn;
    check-names response ignore;
</PRE>

<P><CODE>check-names</CODE> may also be specified in the <CODE>zone</CODE>
statement, in which case it overrides the <CODE>options check-names</CODE>
statement.  When used in a <CODE>zone</CODE> statement, the area is not
specified (because it can be deduced from the zone type).

<A name="AccessControl"><H4>Access Control</H4></A>

<P>Access to the server can be restricted based on the IP address of the
requesting system.  See
<VAR><A HREF="address_list.html">address_match_list</A></VAR> for details
on how to specify IP address lists.

<DL>
<DT><CODE>allow-query</CODE>
<DD>
Specifies which hosts are allowed to ask ordinary questions.
<CODE>allow-query</CODE> may also be specified in the
<CODE>zone</CODE> statement, in which case it overrides the
<CODE>options allow-query</CODE> statement.  If not specified, the default is
to allow queries from all hosts.

<DT><CODE>allow-transfer</CODE>
<DD>
Specifies which hosts are allowed to receive zone transfers from the
server.  <CODE>allow-transfer</CODE> may also be specified in the
<CODE>zone</CODE> statement, in which case it overrides the
<CODE>options allow-transfer</CODE> statement.  If not specified, the default
is to allow transfers from all hosts.
</DL>

<H4>Interfaces</H4>

<P>The interfaces and ports that the server will answer queries from may
be specified using the <CODE>listen-on</CODE> option.  <CODE>listen-on</CODE>
takes an optional port, and an 
<VAR><A HREF="address_list.html">address_match_list</A></VAR>.  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>Multiple <CODE>listen-on</CODE> statements are allowed.  For example,

<PRE>
    listen-on { 5.6.7.8; };
    listen-on port 1234 { !1.2.3.4; 1.2/16; };
</PRE>

<P>If no <CODE>listen-on</CODE> is specified, the server will listen on port
53 on all interfaces.

<H4>Query Address</H4>

<P>If the server doesn't know the answer to a question, it will query
other nameservers.  <CODE>query-source</CODE> specifies the address
and port used for such queries.  If <CODE>address</CODE> is
<CODE>*</CODE> or is omitted, a wildcard IP address
(<CODE>INADDR_ANY</CODE>) will be used.  If <CODE>port</CODE> is
<CODE>*</CODE> or is omitted, a random unprivileged port will be used.
The default is

<PRE>
    query-source address * port *;
</PRE>

<P>Note: <CODE>query-source</CODE> currently applies only to UDP queries;
TCP queries always use a wildcard IP address and a random unprivileged
port.

<A name="ZoneTransfers"><H4>Zone Transfers</H4></A>

<DL>
<DT><CODE>max-transfer-time-in</CODE>
<DD>
Inbound zone transfers (<CODE>named-xfer</CODE> processes) running
longer than this many minutes will be terminated.  The default is 120
minutes (2 hours).

<DT><CODE>transfer-format</CODE>
<DD>
The server supports two zone transfer methods.
<CODE>one-answer</CODE> uses one DNS message per resource record
transferred.  <CODE>many-answers</CODE> packs as many resource records
as possible into a message.  <CODE>many-answers</CODE> is more
efficient, but is only known to be understood by BIND 8.1 and patched
versions of BIND 4.9.5.  The default is <CODE>one-answer</CODE>.
<CODE>transfer-format</CODE> may be
overridden on a per-server basis by using the <CODE>server</CODE> statement.

<DT><CODE>transfers-in</CODE>
<DD>
The maximum number of inbound zone transfers that can be running
concurrently.  The default value is 10.  Increasing
<CODE>transfers-in</CODE> may speed up the convergence of slave zones,
but it also may increase the load on the local system.

<DT><CODE>transfers-out</CODE>
<DD>
This option will be used in the future to limit the number of
concurrent outbound zone transfers.  It is checked for syntax, but is
otherwise ignored.

<DT><CODE>transfers-per-ns</CODE>
<DD>
The maximum number of inbound zone transfers (<CODE>named-xfer</CODE>
processes) that can be concurrently transferring from a given remote
nameserver.  The default value is 2.  Increasing
<CODE>transfers-per-ns</CODE> may speed up the convergence of slave
zones, but it also may increase the load on the remote nameserver.
<CODE>transfers-per-ns</CODE> may be overridden on a per-server basis
by using the <CODE>transfers</CODE> phrase of the <CODE>server</CODE>
statement.
</DL>

<H4>Resource Limits</H4>

<P>The server's usage of many system resources can be limited.  Some
operating systems don't support some of the limits.  On such systems,
a warning will be issued if the unsupported limit is used.  Some
operating systems don't support limiting resources, and on these systems
a <CODE>cannot set resource limits on this system</CODE> message will
be logged.

<P>Scaled values are allowed when specifying resource limits.  For
example, <CODE>1G</CODE> can be used instead of
<CODE>1073741824</CODE> to specify a limit of one gigabyte.
<CODE>unlimited</CODE> requests unlimited use, or the maximum
available amount.  <CODE>default</CODE> uses the limit that was in
force when the server was started.  See
<VAR><AHREF="docdef.html">size_spec</A></VAR> for more details.

<DL>
<DT><CODE>coresize</CODE>
<DD>
The maximum size of a core dump.  The default is <CODE>default</CODE>.

<DT><CODE>datasize</CODE>
<DD>
The maximum amount of data memory the server may use.  The default is
<CODE>default</CODE>.

<DT><CODE>files</CODE>
<DD>
The maximum number of files ther server may have open concurrently.
The default is <CODE>unlimited</CODE>.  <I>Note:</I> on some operating
systems the server cannot set an unlimited value and cannot determine
the maximum number of open files the kernel can support.  On such
systems, choosing <CODE>unlimited</CODE> will cause the server to use
the larger of the <CODE>rlim_max</CODE> for <CODE>RLIMIT_NOFILE</CODE>
and the value returned by <CODE>sysconf(_SC_OPEN_MAX)</CODE>.  If the
actual kernel limit is larger than this value, use <CODE>limit
files</CODE> to specify the limit explicitly.

<DT><CODE>stacksize</CODE>
<DD>
The maximum amount of stack memory the server may use.  The default is
<CODE>default</CODE>.
</DL>

<H4>Periodic Task Intervals</H4>

<DL>
<DT><CODE>cleaning-interval</CODE>
<DD>
The server will remove expired resource records from the cache every
<CODE>cleaning-interval</CODE> minutes.  The default is 60 minutes.  If set
to 0, no periodic cleaning will occur.

<DT><CODE>interface-interval</CODE>
<DD>
The server will scan the network interface list every
<CODE>interface-interval</CODE> minutes.  The default is 60 minutes.
If set to 0, interface scanning will only occur when the configuration
file is loaded.  After the scan, listeners will be started on any new
interfaces (provided they are allowed by the <CODE>listen-on</CODE>
configuration).  Listeners on interfaces that have gone away will be
cleaned up.

<DT><CODE>statistics-interval</CODE>
<DD>
Nameserver statisitics will be logged every <CODE>statistics-interval</CODE>
minutes.  The default is 60.  If set to 0, no statistics will be logged.
</DL>

<H4>Topology</H4>

<P>All other things being equal, when the server chooses a nameserver
to query from a list of nameservers, it prefers the one that is
topologically closest to itself.  The <CODE>topology</CODE> statement
takes an <VAR><A HREF="address_list.html">address_match_list</A></VAR>
and interprets it in a special way.  Each top-level list element is
assigned a distance.  Non-negated elements get a distance based on
their position in the list, where the closer the match is to the start
of the list, the shorter the distance is between it and the server.  A
negated match will be assigned the maximum distance from the server.
If there is no match, the address will get a distance which is further
than any non-negated list element, and closer than any negated
element.  For example,

<PRE>
    topology {
        10/8;
        !1.2.3/24;
        { 1.2/16; 3/8; };
    };
</PRE>

<P>will prefer servers on network 10 the most, followed by hosts on
network 1.2.0.0 (netmask 255.255.0.0) and network 3, with the exception
of hosts on network 1.2.3 (netmask 255.255.255.0), which is preferred least
of all.

<P>The default topology is

<PRE>
    topology { localhost; localnets; };
</PRE>

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