named.conf -- configuration file for named(8)
BIND 8 is much more configurable than previous release of BIND. There
are entirely new areas of configuration, such as access control lists and
categorized logging. Many options that previously applied to all zones
can now be used selectively. These features, plus a consideration of
future configuration needs led to the creation of a new configuration
file format.
General Syntax [Toc] [Back]
A BIND 8 configuration consists of two general features, statements and
comments. All statements end with a semicolon. Many statements can contain
substatements, which are each also terminated with a semicolon.
The following statements are supported:
logging
specifies what the server logs, and where the log messages are sent
options
controls global server configuration options and sets defaults for
other statements
zone
defines a zone
acl
defines a named IP address matching list, for access control and other
uses
key
specifies key information for use in authentication and authorization
trusted-keys
defines DNSSEC keys that are preconfigured into the server and implicitly
trusted
server
sets certain configuration options for individual remote servers
controls
declares control channels to be used by the ndc utility
include
includes another file
The logging and options statements may only occur once per configuration,
while the rest may appear numerous times. Further detail on each statement
is provided in individual sections below.
Comments may appear anywhere that whitespace may appear in a BIND configuration
file. To appeal to programmers of all kinds, they can be written
in C, C++, or shell/perl constructs.
C-style comments start with the two characters /* (slash, star) and end
with */ (star, slash). Because they are completely delimited with these
characters, they can be used to comment only a portion of a line or to
span multiple lines.
C-style comments cannot be nested. For example, the following is not
valid because the entire comment ends with the first */:
/* 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. */
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:
// This is the start of a comment. The next line
// is a new comment, even though it is logically
// part of the previous comment.
Shell-style (or perl-style, if you prefer) comments start with the character
# (hash or pound or number or octothorpe or whatever) and continue
to the end of the physical line, like C++ comments. For example:
# This is the start of a comment. The next line
# is a new comment, even though it is logically
# part of the previous comment.
WARNING: 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, so whatever follows it will be interpreted as
the start of the next statement.
Converting from BIND 4.9.x [Toc] [Back]
BIND 4.9.x configuration files can be converted to the new format by
using src/bin/named/named-bootconf, a shell script that is part of the
BIND 8.2.x source kit.
DOCUMENTATION DEFINITIONS [Toc] [Back] Described below are elements used throughout the BIND configuration file
documentation. Elements which are only associated with one statement are
described only in the section describing that statement.
acl_name
The name of an address_match_list as defined by the acl statement.
address_match_list
A list of one or more ip_addr, ip_prefix, key_id, or acl_name elements,
as described in the ADDRESS MATCH LISTS section.
dotted-decimal
One or more integers valued 0 through 255 separated only by dots
(``.''), such as 123, 45.67 or 89.123.45.67.
domain_name
A quoted string which will be used as a DNS name, for example
"my.test.domain".
path_name
A quoted string which will be used as a pathname, such as
"zones/master/my.test.domain".
ip_addr
An IP address with exactly four elements in dotted-decimal notation.
ip_port
An IP port number. number is limited to 0 through 65535, with values
below 1024 typically restricted to root-owned processes. In some cases
an asterisk (``*'') character can be used as a placeholder to select a
random high-numbered port.
ip_prefix
An IP network specified in dotted-decimal form, followed by ``/'' and
then the number of bits in the netmask. E.g. 127/8 is the network
127.0.0.0 with netmask 255.0.0.0. 1.2.3.0/28 is network 1.2.3.0 with
netmask 255.255.255.240.
key_name
A string representing the name of a shared key, to be used for transaction
security.
number
A non-negative integer with an entire range limited by the range of a C
language signed integer (2,147,483,647 on a machine with 32 bit integers).
Its acceptable value might further be limited by the context in
which it is used.
size_spec
A number, the word unlimited, or the word default.
The maximum value of size_spec is that of unsigned long integers on the
machine. unlimited requests unlimited use, or the maximum available
amount. default uses the limit that was in force when the server was
started.
A number can optionally be followed by a scaling factor: K or k for
kilobytes, M or m for megabytes, and G or g for gigabytes, which scale
by 1024, 1024*1024, and 1024*1024*1024 respectively.
Integer storage overflow is currently silently ignored during conversion
of scaled values, resulting in values less than intended, possibly
even negative. Using unlimited is the best way to safely set a really
large number.
yes_or_no
Either yes or no. The words true and false are also accepted, as are
the numbers 1 and 0.
Syntax
address_match_list = 1*address_match_element
address_match_element = [ "!" ] ( address_match_list /
ip_address / ip_prefix /
acl_name / "key " key_id ) ";"
Definition and Usage [Toc] [Back]
Address match lists are primarily used to determine access control for
various server operations. They are also used to define priorities for
querying other nameservers and to set the addresses on which named will
listen for queries. The elements which constitute an address match list
can be any of the following:
+o an ip-address (in dotted-decimal notation,
+o an ip-prefix (in the '/'-notation),
+o A key_id, as defined by the key statement,
+o the name of an address match list previously defined with the acl
statement, or
+o another address_match_list.
Elements can be negated with a leading exclamation mark (``!''), and the
match list names any, none, localhost and localnets are predefined. More
information on those names can be found in the description of the acl
statement.
The addition of the key clause made the name of this syntactic element
something of a misnomer, since security keys can be used to validate
access without regard to a host or network address. Nonetheless, the
term ``address match list'' is still used throughout the documentation.
When a given IP address or prefix is compared to an address match list,
the list is traversed in order until an element matches. The interpretation
of a match depends on whether the list is being used for access control,
defining listen-on ports, or as a topology, and whether the element
was negated.
When used as an access control list, a non-negated match allows access
and a negated match denies access. If there is no match at all in the
list, access is denied. The clauses allow-query, allow-transfer,
allow-update, allow-recursion, and blackhole all use address match lists
like this. Similarly, the listen-on option will cause the server to not
accept queries on any of the machine's addresses which do not match the
list.
When used with the topology option, a non-negated match returns a distance
based on its position on the list (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.
Because of the first-match aspect of the algorithm, an element that
defines a subset of another element in the list should come before the
broader element, regardless of whether either is negated. For example,
in
1.2.3/24; !1.2.3.13
the 1.2.3.13 element is completely useless, because the algorithm will
match any lookup for 1.2.3.13 to the 1.2.3/24 element. Using
!1.2.3.13; 1.2.3/24
fixes that problem by having 1.2.3.13 blocked by the negation but all
other 1.2.3.* hosts fall through.
THE LOGGING STATEMENT [Toc] [Back] Syntax
logging {
[ channel channel_name {
( file path_name
[ versions ( number | unlimited ) ]
[ size size_spec ]
| syslog ( kern | user | mail | daemon | auth | syslog | lpr |
news | uucp | cron | authpriv | ftp |
local0 | local1 | local2 | local3 |
local4 | local5 | local6 | local7 )
| null );
[ severity ( critical | error | warning | notice |
info | debug [ level ] | dynamic ); ]
[ print-category yes_or_no; ]
[ print-severity yes_or_no; ]
[ print-time yes_or_no; ]
}; ]
[ category category_name {
channel_name; [ channel_name; ... ]
}; ]
...
};
Definition and Usage [Toc] [Back]
The logging statement configures a wide variety of logging options for
the nameserver. Its channel phrase associates output methods, format
options and severity levels with a name that can then be used with the
category phrase to select how various classes of messages are logged.
Only one logging statement is used to define as many channels and categories
as are wanted. If there are multiple logging statements in a configuration,
the first defined determines the logging, and warnings are
issued for the others. If there is no logging statement, the logging
configuration will be:
logging {
category default { default_syslog; default_debug; };
category panic { default_syslog; default_stderr; };
category packet { default_debug; };
category eventlib { default_debug; };
};
The logging configuration is established as soon as the logging statement
is parsed. If you want to redirect messages about processing of the
entire configuration file, the logging statement must appear first. Even
if you do not redirect configuration file parsing messages, we recommend
always putting the logging statement first so that this rule need not be
consciously recalled if you ever do want the parser's messages relocated.
The channel phrase [Toc] [Back]
All log output goes to one or more ``channels''; you can make as many of
them as you want.
Every channel definition must include a clause that says whether messages
selected for the channel go to a file, to a particular syslog facility,
or are discarded. It can optionally also limit the message severity
level that will be accepted by the channel (default is info), and whether
to include a time stamp generated by named, the category name, or severity
level. The default is not to include any of those three.
The word null as the destination option for the channel will cause all
messages sent to it to be discarded; other options for the channel are
meaningless.
The file clause 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.
The size option for files is simply a hard ceiling on log growth. If the
file ever exceeds the size, then named will just not write anything more
to it until the file is reopened; exceeding the size does not automatically
trigger a reopen. The default behavior is to not limit the size of
the file.
If you use the version logfile option, then named will retain that many
backup versions of the file by renaming them when opening. For example,
if you choose to keep 3 old versions of the file lamers.log then just
before it is opened lamers.log.1 is renamed to lames.log.2, lamers.log.0
is renamed to lamers.log.1, and lamers.log is renamed to lamers.log.0.
No rolled versions are kept by default; any existing log file is simply
appended. The unlimited keyword is synonymous with 99 in current BIND
releases. Example usage of size and versions options:
channel an_example_level {
file "lamers.log" versions 3 size 20m;
print-time yes;
print-category yes;
};
The argument for the syslog clause is a syslog facility as described in
the syslog(3) manual page. How syslogd will handle messages sent to this
facility is described in the syslog.conf(5) manual page. If you have a
system which uses a very old version of syslog that only uses two arguments
to the openlog() function, then this clause is silently ignored.
The severity clause works like syslog's ``priorities'', except that they
can also be used if you are writing straight to a file rather than using
syslog. Messages which are not at least of the severity level given
will not be selected for the channel; messages of higher severity levels
will be accepted.
If you are using syslog, then the syslog.conf priorities will also determine
what eventually passes through. For example, defining a channel
facility and severity as daemon and debug but only logging daemon.warning
via syslog.conf will cause messages of severity info and notice to be
dropped. If the situation were reversed, with named writing messages of
only warning or higher, then syslogd would print all messages it received
from the channel.
The server can supply extensive debugging information when it is in
debugging mode. If the server's global debug level is greater than zero,
then debugging mode will be active. The global debug level is set either
by starting the named server with the -d flag followed by a positive
integer, or by sending the running server the SIGUSR1 signal (for example,
by using ndc trace). The global debug level can be set to zero, and
debugging mode turned off, by sending the server the SIGUSR2 signal (as
with ndc notrace). All debugging messages in the server have a debug
level, and higher debug levels give more more detailed output. Channels
that specify a specific debug severity, e.g.
channel specific_debug_level {
file "foo";
severity debug 3;
};
will get debugging output of level 3 or less any time the server is in
debugging mode, regardless of the global debugging level. Channels with
dynamic severity use the server's global level to determine what messages
to print.
If print-time has been turned on, then the date and time will be logged.
print-time may be specified for a syslog channel, but is usually pointless
since syslog also prints the date and time. If print-category is
requested, then the category of the message will be logged as well.
Finally, if print-severity is on, then the severity level of the message
will be logged. The print- options may be used in any combination, and
will always be printed in the following order: time, category, severity.
Here is an example where all three print- options are on:
28-Apr-1997 15:05:32.863 default: notice: Ready to answer queries.
There are four predefined channels that are used for default logging as
follows. How they are used used is described in the next section, The
category phrase.
channel default_syslog {
syslog daemon; # send to syslog's daemon facility
severity info; # only send priority info and higher
};
channel default_debug {
file "named.run"; # write to named.run in the working directory
# Note: stderr is used instead of "named.run"
# if the server is started with the -f option.
severity dynamic; # log at the server's current debug level
};
channel default_stderr { # writes to stderr
file "<stderr>"; # this is illustrative only; there's currently
# no way of specifying an internal file
# descriptor in the configuration language.
severity info; # only send priority info and higher
};
channel null {
null; # toss anything sent to this channel
};
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.
The category phrase [Toc] [Back]
There are many categories, so you can send the logs you want to see wherever
you want, without seeing logs you don't want. If you don't specify
a list of channels for a category, then log messages in that category
will be sent to the default category instead. If you don't specify a
default category, the following ``default default'' is used:
category default { default_syslog; default_debug; };
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:
channel my_security_channel {
file "my_security_file";
severity info;
};
category security { my_security_channel;
default_syslog; default_debug; };
To discard all messages in a category, specify the null channel:
category lame-servers { null; };
category cname { null; };
The following categories are available:
default
The catch-all. Many things still aren't classified into categories,
and they all end up here. Also, if you don't specify any channels for
a category, the default category is used instead. If you do not define
the default category, the following definition is used:
category default { default_syslog; default_debug; };
config
High-level configuration file processing.
parser
Low-level configuration file processing.
queries
A short log message is generated for every query the server receives.
lame-servers
Messages like ``Lame server on ...''
statistics
Statistics.
panic
If the server has to shut itself down due to an internal problem, it
will log the problem in this category as well as in the problem's
native category. If you do not define the panic category, the following
definition is used:
category panic { default_syslog; default_stderr; };
update
Dynamic updates.
update-security
Denied dynamic updates due to access controls.
ncache
Negative caching.
xfer-in
Zone transfers the server is receiving.
xfer-out
Zone transfers the server is sending.
db
All database operations.
eventlib
Debugging info from the event system. Only one channel may be specified
for this category, and it must be a file channel. If you do not
define the eventlib category, the following definition is used:
category eventlib { default_debug; };
packet
Dumps of packets received and sent. Only one channel may be specified
for this category, and it must be a file channel. If you do not define
the packet category, the following definition is used:
category packet { default_debug; };
notify
The NOTIFY protocol.
cname
Messages like ``... points to a CNAME''.
security
Approved/unapproved requests.
os
Operating system problems.
insist
Internal consistency check failures.
maintenance
Periodic maintenance events.
load
Zone loading messages.
response-checks
Messages arising from response checking, such as ``Malformed response
...'', ``wrong ans. name ...'', ``unrelated additional info ...'',
``invalid RR type ...'', and ``bad referral ...''.
THE OPTIONS STATEMENT [Toc] [Back] Syntax
options {
[ hostname hostname_string; ]
[ version version_string; ]
[ directory path_name; ]
[ named-xfer path_name; ]
[ dump-file path_name; ]
[ memstatistics-file path_name; ]
[ pid-file path_name; ]
[ statistics-file path_name; ]
[ auth-nxdomain yes_or_no; ]
[ deallocate-on-exit yes_or_no; ]
[ dialup yes_or_no; ]
[ fake-iquery yes_or_no; ]
[ fetch-glue yes_or_no; ]
[ has-old-clients yes_or_no; ]
[ host-statistics yes_or_no; ]
[ host-statistics-max number; ]
[ multiple-cnames yes_or_no; ]
[ notify ( yes_or_no | explicit ); ]
[ suppress-initial-notify yes_or_no; ]
[ recursion yes_or_no; ]
[ rfc2308-type1 yes_or_no; ]
[ use-id-pool yes_or_no; ]
[ treat-cr-as-space yes_or_no; ]
[ also-notify yes_or_no; ]
[ forward ( only | first ); ]
[ forwarders { [ in_addr ; [ in_addr ; ... ] ] }; ]
[ check-names ( master | slave | response ) ( warn | fail | ignore ); ]
[ allow-query { address_match_list }; ]
[ allow-recursion { address_match_list }; ]
[ allow-transfer { address_match_list }; ]
[ blackhole { address_match_list }; ]
[ listen-on [ port ip_port ] { address_match_list }; ]
[ query-source [ address ( ip_addr | * ) ]
[ port ( ip_port | * ) ] ; ]
[ lame-ttl number; ]
[ max-transfer-time-in number; ]
[ max-ncache-ttl number; ]
[ min-roots number; ]
[ serial-queries number; ]
[ transfer-format ( one-answer | many-answers ); ]
[ transfers-in number; ]
[ transfers-out number; ]
[ transfers-per-ns number; ]
[ transfer-source ip_addr; ]
[ maintain-ixfr-base yes_or_no; ]
[ max-ixfr-log-size number; ]
[ coresize size_spec ; ]
[ datasize size_spec ; ]
[ files size_spec ; ]
[ stacksize size_spec ; ]
[ cleaning-interval number; ]
[ heartbeat-interval number; ]
[ interface-interval number; ]
[ statistics-interval number; ]
[ topology { address_match_list }; ]
[ sortlist { address_match_list }; ]
[ rrset-order { order_spec ; [ order_spec ; ... ] }; ]
[ preferred-glue ( A | AAAA ); ]
[ edns-udp-size number; ]
};
Definition and Usage [Toc] [Back]
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.
Server Information [Toc] [Back]
hostname
This defaults to the hostname of the machine hosting the nameserver as
found by gethostname(). Its prime purpose is to be able to identify
which of a number of anycast servers is actually answering your queries
by sending a txt query for hostname.bind in class chaos to the anycast
server and geting back a unique name. Setting the hostname to a empty
string ("") will disable processing of the queries.
version
The version the server should report via the ndc command or via a query
of name version.bind in class chaos. The default is the real version
number of the server, but some server operators prefer the string (
surely you must be joking ).
Pathnames [Toc] [Back]
directory
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.
named-xfer
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 ).
dump-file
The pathname of the file the server dumps the database to when it
receives SIGINT signal (as sent by ndc dumpdb ). If not specified, the
default is named_dump.db.
memstatistics-file
The pathname of the file the server writes memory usage statistics to
on exit, if deallocate-on-exit is yes. If not specified, the default
is named.memstats.
pid-file
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.
statistics-file
The pathname of the file the server appends statistics to when it
receives SIGILL signal (from ndc stats). If not specified, the default
is named.stats.
Boolean Options [Toc] [Back]
auth-nxdomain
If yes, then the AA bit is always set on NXDOMAIN responses, even if
the server is not actually authoritative. The default is no. Turning
will allow older clients that require AA to be set to accept NXDOMAIN
responses to work.
deallocate-on-exit
If yes, then when the server exits it will painstakingly deallocate
every object it allocated, and then write a memory usage report to the
memstatistics-file. The default is no, because it is faster to let the
operating system clean up. deallocate-on-exit is handy for detecting
memory leaks.
dialup
If yes, then the server treats all zones as if they are doing zone
transfers across a dial on demand dialup link, which can be brought up
by traffic originating from this server. This has different effects
according to zone type and concentrates the zone maintenance so that it
all happens in a short interval, once every heartbeat-interval and
hopefully during the one call. It also suppresses some of the normal
zone maintenance traffic. The default is no. The dialup option may
also be specified in the zone statement, in which case it overrides the
options dialup statement.
If the zone is a master 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 slave to verify the
zone while the call us up.
If the zone is a slave or stub then the server will suppress the zone
regular zone up to date queries and only perform the when the
heartbeat-interval expires.
fake-iquery
If yes, the server will simulate the obsolete DNS query type IQUERY.
The default is no.
fetch-glue
If yes (the default), the server will fetch ``glue'' resource records
it doesn't have when constructing the additional data section of a
response. fetch-glue no can be used in conjunction with recursion no
to prevent the server's cache from growing or becoming corrupted (at
the cost of requiring more work from the client).
has-old-clients
Setting the option to yes, is equivalent to setting the following three
options: auth-nxdomain yes;, maintain-ixfr-base yes;, and rfc2308-type1
no;
The use of has-old-clients with auth-nxdomain, maintain-ixfr-base, and
rfc2308-type1 is order dependent.
host-statistics
If yes, then statistics are kept for every host that the the nameserver
interacts with. The default is no. Note: turning on host-statistics
can consume huge amounts of memory.
maintain-ixfr-base
If yes, a IXFR database file is kept for all dynamically updated zones.
This enables the server to answer IXFR queries which can speed up zone
transfers enormously. The default is no.
multiple-cnames
If yes, then multiple CNAME resource records will be allowed for a
domain name. The default is no. 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.
notify
If yes (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. If explicit, the DNS NOTIFY messages
will only be sent to the addresses in the also-notify list. The notify
option may also be specified in the zone statement, in which case it
overrides the options notify statement.
suppress-initial-notify
If yes, suppress the initial notify messages when the server first
loads. The default is no.
recursion
If yes, 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 yes. See also fetch-glue
above.
rfc2308-type1
If yes, the server will send NS records along with the SOA record for
negative answers. You need to set this to no 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 no.
use-id-pool
If yes, 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 by the server. The default is no.
treat-cr-as-space
If yes, the server will treat CR characters the same way it treats a
space or tab. This may be necessary when loading zone files on a UNIX
system that were generated on an NT or DOS machine. The default is no.
Also-Notify [Toc] [Back]
also-notify
Defines a global list of IP addresses that also get sent NOTIFY messages
whenever a fresh copy of the zone is loaded. This helps to ensure that
copies of the zones will quickly converge on ``stealth'' servers. If an
also-notify list is given in a zone statement, it will override the
options also-notify statement. When a zone notify statement is set to no,
the IP addresses in the global also-notify list will not get sent NOTIFY
messages for that zone. The default is the empty list (no global notification
list).
Forwarding [Toc] [Back]
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.
forward
This option is only meaningful if the forwarders list is not empty. A
value of first, 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 only is specified, the server will only
query the forwarders.
forwarders
Specifies the IP addresses to be used for forwarding. The default is
the empty list (no forwarding).
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
forward only/first behavior, or to not forward at all. See THE ZONE
STATEMENT section for more information.
Future versions of BIND 8 will provide a more powerful forwarding system.
The syntax described above will continue to be supported.
Name Checking [Toc] [Back]
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.
Three checking methods are available:
ignore
No checking is done.
warn
Names are checked against their expected client contexts. Invalid
names are logged, but processing continues normally.
fail
Names are checked against their expected client contexts. Invalid
names are logged, and the offending data is rejected.
The server can check names three areas: master zone files, slave zone
files, and in responses to queries the server has initiated. If
check-names response fail 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.
The defaults are:
check-names master fail;
check-names slave warn;
check-names response ignore;
check-names may also be specified in the zone statement, in which case it
overrides the options check-names statement. When used in a zone statement,
the area is not specified (because it can be deduced from the zone
type).
Access Control [Toc] [Back]
Access to the server can be restricted based on the IP address of the
requesting system or via shared secret keys. See ADDRESS MATCH LISTS for
details on how to specify access criteria.
allow-query
Specifies which hosts are allowed to ask ordinary questions.
allow-query may also be specified in the zone statement, in which case
it overrides the options allow-query statement. If not specified, the
default is to allow queries from all hosts.
allow-recursion
Specifies which hosts are allowed to ask recursive questions. If not
specified, the default is to allow recursive queries from all hosts.
allow-transfer
Specifies which hosts are allowed to receive zone transfers from the
server. allow-transfer may also be specified in the zone statement,
in which case it overrides the options allow-transfer statement. If
not specified, the default is to allow transfers from all hosts.
blackhole
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.
Interfaces [Toc] [Back]
The interfaces and ports that the server will answer queries from may be
specified using the listen-on option. listen-on takes an optional port,
and an address match list. The server will listen on all interfaces
allowed by the address match list. If a port is not specified, port 53
will be used.
Multiple listen-on statements are allowed. For example,
listen-on { 5.6.7.8; };
listen-on port 1234 { !1.2.3.4; 1.2/16; };
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.
If no listen-on is specified, the server will listen on port 53 on all
interfaces.
Query Address [Toc] [Back]
If the server doesn't know the answer to a question, it will query other
nameservers. query-source specifies the address and port used for such
queries. If address is * or is omitted, a wildcard IP address (
INADDR_ANY) will be used. If port is * or is omitted, a random unprivileged
port will be used. The default is
query-source address * port *;
Note: query-source currently applies only to UDP queries; TCP queries
always use a wildcard IP address and a random unprivileged port.
Zone Transfers [Toc] [Back]
max-transfer-time-in
Inbound zone transfers ( named-xfer processes) running longer than this
many minutes will be terminated. The default is 120 minutes (2 hours).
transfer-format
The server supports two zone transfer methods. one-answer uses one DNS
message per resource record transferred. many-answers packs as many
resource records as possible into a message. many-answers is more
efficient, but is only known to be understood by BIND 8.1 and patched
versions of BIND 4.9.5. The default is one-answer. transfer-format
may be overridden on a per-server basis by using the server statement.
transfers-in
The maximum number of inbound zone transfers that can be running concurrently.
The default value is 10. Increasing transfers-in may speed
up the convergence of slave zones, but it also may increase the load on
the local system.
transfers-out
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.
transfers-per-ns
The maximum number of inbound zone transfers ( named-xfer processes)
that can be concurrently transferring from a given remote nameserver.
The default value is 2. Increasing transfers-per-ns may speed up the
convergence of slave zones, but it also may increase the load on the
remote nameserver. transfers-per-ns may be overridden on a per-server
basis by using the transfers phrase of the server statement.
transfer-source
transfer-source determines which local address will be bound to the TCP
connection used to fetch all zones transferred inbound by the server.
If not set, it defaults to a system controlled value which will usually
be the address of the interface ``closest to`` the remote end. This
address must appear in the remote end's allow-transfer option for the
zones being transferred, if one is specified. This statement sets the
transfer-source for all zones, but can be overridden on a per-zone
basis by including a transfer-source statement within the zone block in
the configuration file.
Resource Limits [Toc] [Back]
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
cannot set resource limits on this system
message will be logged.
Scaled values are allowed when specifying resource limits. For example,
1G can be used instead of 1073741824 to specify a limit of one gigabyte.
unlimited requests unlimited use, or the maximum available amount.
default uses the limit that was in force when the server was started.
See the definition of size_spec in the DOCUMENTATION DEFINITIONS section
for more details.
coresize
The maximum size of a core dump. The default value is default.
datasize
The maximum amount of data memory the server may use. The default
value is default.
files
The maximum number of files the server may have open concurrently. The
default value is unlimited. Note that 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
unlimited will cause the server to use the larger of the rlim_max from
getrlimit(RLIMIT_NOFILE) and the value returned by
sysconf(_SC_OPEN_MAX). If the actual kernel limit is larger than this
value, use limit files to specify the limit explicitly.
max-ixfr-log-size
The max-ixfr-log-size will be used in a future release of the server to
limit the size of the transaction log kept for Incremental Zone Transfer.
stacksize
The maximum amount of stack memory the server may use. The default
value is default.
Periodic Task Intervals [Toc] [Back]
cleaning-interval
The server will remove expired resource records from the cache every
cleaning-interval minutes. The default is 60 minutes. If set to 0, no
periodic cleaning will occur.
heartbeat-interval
The server will perform zone maintenance tasks for all zones marked
dialup yes 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.
interface-interval
The server will scan the network interface list every
interface-interval 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 listen-on configuration). Listeners
on interfaces that have gone away will be cleaned up.
statistics-interval
Nameserver statistics will be logged every statistics-interval minutes.
The default is 60. If set to 0, no statistics will be logged.
Topology [Toc] [Back]
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 topology statement takes an address match
list 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 nonnegated
list element, and closer than any negated element. For example,
topology {
10/8;
!1.2.3/24;
{ 1.2/16; 3/8; };
};
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.
The default topology is
topology { localhost; localnets; };
Resource Record sorting [Toc] [Back]
When returning multiple RRs, the nameserver will normally return them in
Round Robin, 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.
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.
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.
The sortlist statement takes an address match list and interprets it even
more specially than the topology statement does.
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.
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, 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.
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.
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
};
};
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.
sortlist {
{ localhost; localnets; };
{ localnets; };
};
RRset Ordering [Toc] [Back]
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 random shuffle of
the records as they are returned is wanted. The rrset-order 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).
An order_spec is defined as follows:
[ class class_name ][ type type_name ][ name "FQDN" ] order ordering
If no class is specified, the default is ANY. If no Ictype is specified,
the default is ANY. If no name is specified, the default is "*".
The legal values for ordering are:
fixed Records are returned in the order they are defined in the zone
file.
random Records are returned in some random order.
cyclic Records are returned in a round-robin order.
For example:
rrset-order {
class IN type A name "rc.vix.com" order random;
order cyclic;
};
will cause any responses for type A records in class IN that have
"rc.vix.com" as a suffix, to always be returned in random order. All
other records are returned in cyclic order.
If multiple rrset-order statements appear, they are not combined--the
last one applies.
If no rrset-order statement is specified, a default one of:
rrset-order { class ANY type ANY name "*" order cyclic ; };
is used.
Glue Ordering [Toc] [Back]
When running a root nameserver it is sometimes necessary to ensure that
other nameservers that are priming are successful. This requires that
glue A records for at least of the nameservers are returned in the answer
to a priming query. This can be achieved by setting preferred-glue A;
which will add A records before other types in the additional section.
EDNS [Toc] [Back]
Some firewalls fail to pass EDNS/UDP messages that are larger than certain
size, 512 or the UDP reassembly buffer. To allow EDNS to work
across such firewalls it is necessary to advertise a EDNS buffer size
that is small enough to not trigger failures. edns-udp-size can be use
to adjust the advertised size. Values less than 512 will be increased to
512 and values greater than 4096 will be truncated to 4096.
Tuning [Toc] [Back]
lame-ttl
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)
max-ncache-ttl
To reduce network traffic and increase performance the server store
negative answers. max-ncache-ttl is used to set a maximum retention
time for these answers in the server is seconds. The default
max-ncache-ttl is 10800 seconds (3 hours). max-ncache-ttl 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.
min-roots
The minimum number of root servers that is required for a request for
the root servers to be accepted. Default is 2.
Syntax
zone domain_name [ ( in | hs | hesiod | chaos ) ] {
type master;
file path_name;
[ check-names ( warn | fail | ignore ); ]
[ allow-update { address_match_list }; ]
[ allow-query { address_match_list }; ]
[ allow-transfer { address_match_list }; ]
[ forward ( only | first ); ]
[ forwarders { [ ip_addr ; [ ip_addr ; ... ] ] }; ]
[ dialup yes_or_no; ]
[ notify ( yes_or_no | explicit ); ]
[ also-notify { ip_addr; [ ip_addr; ... ] };
[ pubkey number number number string; ]
};
zone domain_name [ ( in | hs | hesiod | chaos ) ] {
type ( slave | stub );
[ f
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