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

<HR>

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

<PRE>
options {
  [ version <VAR>version_string</VAR>; ]
  [ 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>; ]
  [ dialup <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>; ]
  [ has-old-clients <VAR><A HREF="docdef.html">yes_or_no</A></VAR>; ]
  [ host-statistics <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>; ]
  [ rfc2308-type1 <VAR><A HREF="docdef.html">yes_or_no</A></VAR>; ]
  [ use-id-pool <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> }; ]
  [ allow-recursion { <VAR>address_match_list</VAR> }; ]
  [ blackhole { <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> | * ) ] ; ]
  [ lame-ttl <VAR>number</VAR>; ]
  [ max-transfer-time-in <VAR>number</VAR>; ]
  [ max-ncache-ttl <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>; ]
  [ maintain-ixfr-base <VAR><A HREF="docdef.html">yes_or_no</A></VAR>; ]
  [ max-ixfr-log-size <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>; ]
  [ heartbeat-interval <VAR>number</VAR>; ]
  [ interface-interval <VAR>number</VAR>; ]
  [ statistics-interval <VAR>number</VAR>; ]
  [ <A HREF="#topology">topology</A> { <VAR>address_match_list</VAR> }; ]
  [ <A HREF="#sortlist">sortlist</A> { <VAR>address_match_list</VAR> }; ]
  [ rrset-order { <VAR>order_spec</VAR> ; [ <VAR>order_spec</VAR> ; ... ] ] }; 
};
</PRE>
<HR>

<A NAME="Usage"><H3>Definition and Usage</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>version</CODE>
<DD>
The version the server should report via the <VAR>ndc</VAR> command
or via a query of name <CODE>version.bind</CODE> in class <I>chaos</I>.
The default is the real version number of ths server, but some server
operators prefer the string <CODE>"surely you must be joking"</CODE>.

<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>dialup</CODE>
<DD>
If <CODE>yes</CODE>, then the server treats all zones as if they are
doing zone transfers across a dial on demand dialup link, which can
be brought up by traffic originating from this server.  This has
different effects according to zone type and concentrates the zone
maintenance so that it all happens in a short interval, once every 
<CODE>heartbeat-interval</CODE> and hopefully during the one call.
It also suppresses some of the normal zone maintainance traffic.
The default is <CODE>no</CODE>. The <CODE>dialup</CODE>
option may also be specified in the <CODE>zone</CODE> statement, in which
case it overrides the <CODE>options dialup</CODE> statement.

<P>
If the zone is a <CODE>master</CODE> then the server will send out
NOTIFY request to all the slaves.  This will trigger the zone up to
date checking in the slave (providing it supports NOTIFY) allowing
the <CODE>slave</CODE> to verify the zone while the call us up.

<P>
If the zone is a <CODE>slave</CODE> or <CODE>stub</CODE> then the server
will suppress the zone regular zone up to date queries and only perform
the when the <CODE>heartbeat-interval</CODE> expires.

<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>has-old-clients</CODE>
<DD>
Setting the option to <CODE>yes</CODE> is equivalent to setting the follow
three options <CODE>auth-nxdomain yes;</CODE>, <CODE>maintain-ixfr-base
yes;</CODE> and <CODE>rfc2308-type1 no;</CODE>.
The use of <CODE>has-old-clients</CODE> with <CODE>auth-nxdomain</CODE>,
<CODE>maintain-ixfr-base</CODE> and <CODE>rfc2308-type1</CODE> is order
dependant.

<DT><CODE>host-statistics</CODE>
<DD>
If <CODE>yes</CODE>, then statistics are kept for every host that the
the nameserver interacts with.  The default is <CODE>no</CODE>.  <I>Note:</I>
turning on <CODE>host-statistics</CODE> can consume huge amounts of memory.

<DT><CODE>maintain-ixfr-base</CODE>
<DD>
If <CODE>yes</CODE>, then a transaction log is kept for 
Incremental Zone Transfer. The default is <CODE>no</CODE>. 

<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.

<DT><CODE>rfc2308-type1</CODE>
<DD>
If <CODE>yes</CODE>, the server will send NS records along with the SOA
record for negative answers.
You need to set this to <CODE>no</CODE> if you have an old BIND
server using you as a forwarder that does not understand negative answers
which contain both SOA and NS records or you have an old version of sendmail.
The correct fix is to upgrade the broken server or sendmail.
The default is <CODE>no</CODE>.

<DT><CODE>use-id-pool</CODE>
<DD>
If <CODE>yes</CODE>, the server will keep track of its own outstanding
query ID's to avoid duplication and increase randomness.  This will result
in 128KB more memory being consumed the server.
The default is <CODE>no</CODE>.
</DL>

<A NAME="Forwarding"><H4>Forwarding</H4></A>

<P>The forwarding facility can be used to create a large site-wide
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>Forwarding can also be configured on a per-zone basis, allowing for
the global forwarding options to be overridden in a variety of ways.
You can set particular zones to use different forwarders, or have
different <CODE>forward only/first</CODE> behavior, or to not forward
at all.  See the <A HREF="zone.html"><CODE>zone</CODE></A> statement
for more information.

<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
<A HREF="zone.html"><CODE>zone</CODE></A>
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.

<DT><CODE>allow-recursion</CODE>
<DD>
Specifies which hosts are allowed to make recursive queries through this
server.  If not specified, the default is to allow transfers from all hosts.

<DT><CODE>blackhole</CODE>
<DD>
Specifies a list of addresses that the server will not accept queries from
or use to resolve a query.  Queries from these addresses will not be
responded to.
</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>

will enable the nameserver 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>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><A HREF="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 the 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>max-ixfr-log-size</CODE>
<DD>
The <CODE>max-ixfr-log-size</CODE> will be used in a future release of 
the server to limit the size of the 
transaction log kept for Incremental Zone Transfer. 

<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>heartbeat-interval</CODE>
<DD>
The server will perform zone maintenance tasks for all zones marked
<CODE>dialup yes</CODE> whenever this interval expires.
The default is 60 minutes. Reasonable values are up to 1 day (1440 minutes).
If set to 0, no zone maintenance for these zones 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 statistics will be logged every <CODE>statistics-interval</CODE>
minutes.  The default is 60.  If set to 0, no statistics will be logged.
</DL>

<H4><A NAME="topology">Topology</A></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>

<H4><A NAME="sortlist">Resource Record sorting</A></H4>

<P>
When returning multiple RRs,
the nameserver will normally return them in
<B>Round Robin</B>,
i.e. after each request, the first RR is put to the end of the list.
As the order of RRs is not defined, this should not cause any problems.
</P>
<P>
The client resolver code should re-arrange the RRs as appropriate,
i.e. using any addresses on the local net in preference to other addresses.
However, not all resolvers can do this, or are not correctly configured.
</P>
<P>
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 nameservers, not all the clients.
</P>
<P>
The sortlist statement takes an address match list and interprets it even
more specially than the <A HREF="#topology">topology</A> statement does.
</P>
<P>
Each top level statement in the sortlist must itself be an explicit
address match list with one or two elements.  The first element
(which may be an IP address, an IP prefix, an ACL name or nested
address match list) of each top level list is checked against the
source address of the query until a match is found.
</P>
<P>
Once the source address of the query has been matched, if the top level
statement contains only one element, the actual primitive element that
matched the source address is used to select the address in the response
to move to the beginning of the response.  If the statement is a list
of two elements, then the second element is treated like the address
match list in a topology statement.  Each top level element is assigned
a distance and the address in the response with the minimum distance is
moved to the beginning of the response.
</P>
<P>
In the following example, any queries received from any of the addresses
of the host itself will get responses preferring addresses on any of
the locally connected networks.  Next most preferred are addresses on
the 192.168.1/24 network, and after that either the 192.168.2/24 or
192.168.3/24 network with no preference shown between these two networks.
Queries received from a host on the 192.168.1/24 network will prefer
other addresses on that network to the 192.168.2/24 and 192.168.3/24
networks.  Queries received from a host on the 192.168.4/24 or the
192.168.5/24 network will only prefer other addresses on their
directly connected networks.
<PRE>
sortlist {
           { localhost;         // IF   the local host
             { localnets;       // THEN first fit on the
               192.168.1/24;    //      following nets
               { 192,168.2/24; 192.168.3/24; }; }; };
           { 192.168.1/24;      // IF   on class C 192.168.1
             { 192.168.1/24;    // THEN use .1, or .2 or .3
               { 192.168.2/24; 192.168.3/24; }; }; };
           { 192.168.2/24;      // IF   on class C 192.168.2
             { 192.168.2/24;    // THEN use .2, or .1 or .3
               { 192.168.1/24; 192.168.3/24; }; }; };
           { 192.168.3/24;      // IF   on class C 192.168.3
             { 192.168.3/24;    // THEN use .3, or .1 or .2
               { 192.168.1/24; 192.168.2/24; }; }; };
           { { 192.168.4/24; 192.168.5/24; }; // if .4 or .5, prefer that net
           };
};
</PRE>
The following example will give reasonable behaviour for the local host
and hosts on directly connected networks.  It is similar to the behavior
of the address sort in BIND 4.9.x.  Responses sent to queries from the
local host will favor any of the directly connected networks.  Responses
sent to queries from any other hosts on a directly connected network will
prefer addresses on that same network.  Responses to other queries will
not be sorted.
<PRE>
sortlist {
            { localhost; localnets; };
            { localnets; };
};
</PRE>
<!--
 * XXX - it would be nice to have an ACL called "source" that matched the
 *       source address of a query so that a host could be configured to
 *       automatically prefer itself, and an ACL called "sourcenet", that
 *       would return the primitive IP match element that matched the source
 *       address so that you could do:
 *          { localnets; { sourcenet; { other stuff ...}; };
 *       and automatically get similar behaviour to what you get with:
 *          { localnets; };
-->
</P>

<a name="RrsetOrder">
<H4>RRset Ordering</H4>

<P>When multiple records are returned in an answer it may be useful to
configure the order the records are placed into the response. For example the
records for a zone might be configured to always be returned in the order they
are defined in the zone file.  Or perhaps a <i>random</i> shuffle of the
records as they are returned is wanted. The <var>rrset-order</var> statement
permits configuration of the ordering made of the records in a multiple record
response. The default, if no ordering is defined, is a cyclic ordering (round
robin).

<P>An <var>order_spec</var> is defined as follows:

<PRE>
  [ <var>class</var> class_name ][ <var>type</var> type_name ][ <var>name</var> "FQDN" ] <var>order</var> ordering
</PRE>

<P>If no <var>class</var> is specified, the default is <code>ANY</code>. If no
<var>type</var> is specified, the default is <code>ANY</code>. If no
<var>name</var> is specified, the default is <code>"*"</code>. 

<P>The legal values for <code>ordering</code> are:

<DL>
<DT><code>fixed</code>
<DD>Records are returned in the order they are defined in the zone file.

<DT><code>random</code>
<DD>Records are returned in some random order.

<DT><code>cyclic</code>
<DD>Records are returned in a round-robin order.

</DL>


<P>For example:

<PRE>
    rrset-order {
	class IN type A name "rc.vix.com" order random;
        order cyclic;
    };
</PRE>

<P>will cause any responses for type <VAR>A</VAR> records in class
<VAR>IN</VAR> that have "rc.vix.com" as a suffix, to always be returned in
random order. All other records are returned in cyclic order.

<P>If multiple <code>rrset-order</code> statements appear, they are not
combined--the last one applies.

<P>If no <code>rrset-order</code> statement is specified, then a default one
of:

<pre>
    rrset-order { class ANY type ANY name "*" order cyclic ; };
</pre>

<P>is used.

<H4>Tuning</H4>

<DL>
<DT><CODE>lame-ttl</CODE>
<DD>
Sets the number of seconds to cache a lame server indication.
0 disables caching.  Default is 600 (10 minutes).  Maximum value is 1800 (30 minutes).
<DT><CODE>max-ncache-ttl</CODE>
<DD>
To reduce network traffic and increase performance the server stores negative
answers.  <CODE>max-ncache-ttl</CODE> is used to set a maximum retention time
for these answers in the server is seconds.  The default <CODE>max-ncache-ttl</CODE> is
10800 seconds (3 hours).  <CODE>max-ncache-ttl</CODE> cannot exceed the
maximum retention time for ordinary (positive) answers (7 days) and will be
silently truncated to 7 days if set to a value which is greater that 7 days.
</DL>
<HR>

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