BIND 9 configuration is broadly similar
to BIND 8; however, there are a few new areas
of configuration, such as views. BIND
8 configuration files should work with few alterations in BIND
9, although more complex configurations should be reviewed to check
if they can be more efficiently implemented using the new features
found in BIND 9.
BIND 4 configuration files can be converted to the new format
using the shell scriptcontrib/named-bootconf/named-bootconf.sh.
Following is a list of elements used throughout the BIND configuration
file documentation:
| The name of an |
| A list of one or more |
| A quoted string which will be used as |
| One to four integers valued 0 through |
| An IPv4 address with exactly four elements |
| An IPv6 address, such as 2001:db8::1234. |
| An |
| An IP port |
| An IP network specified as an |
| A |
| A list of one or more |
| A non-negative 32 bit integer |
| A quoted string which will be used as |
| A number, the word
A The value must be representable as a 64-bit unsigned integer |
| Either |
| One of |
address_match_list= address_match_list_element ;
[ address_match_list_element; ... ]address_match_list_element= [ ! ] (ip_address [/length] |
key key_id | acl_name | { address_match_list } )
Address match lists are primarily used to determine access
control for various server operations. They are also used in
the listen-on and sortlist
statements. The elements
which constitute an address match list can be any of the following:
- an IP address (IPv4 or IPv6)
- an IP prefix (in `/' notation)
- a key ID, as defined by the key statement
- the name of an address match list defined with
the acl statement - a nested address match list enclosed in braces
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 in a sortlist,
and whether the element was negated.
When used as an access control list, a non-negated match allows
access and a negated match denies access. If there is no match,
access is denied. The clauses allow-notify,
allow-query, allow-transfer,
allow-update, allow-update-forwarding,
and blackhole all
use address match lists 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.
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 BIND 9 comment syntax allows for comments to appear
anywhere that white space may appear in a BIND configuration
file. To appeal to programmers of all kinds, they can be written
in the C, C++, or shell/perl style.
/* This is a BIND comment as in C */// This is a BIND comment as in C++# This is a BIND comment as in common UNIX shells and perl
Comments may appear anywhere that whitespace may appear in
a BIND configuration file.
C-style comments start with the two characters /* (slash,
star) and end with */ (star, slash). Because they are completely
delimited with these characters, they can be used to comment only
a portion of a line or to span multiple lines.
C-style comments cannot be nested. For example, the following
is not valid because the entire comment ends with the first */:
/* 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 # (number sign) and continue to the end of the
physical line, as in 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.
A BIND 9 configuration consists of statements and comments.
Statements end with a semicolon. Statements and comments are the
only elements that can appear without enclosing braces. Many
statements contain a block of sub-statements, which are also
terminated with a semicolon.
The following statements are supported:
acl | defines a named IP address |
controls | declares control channels to be used |
include | includes a file. |
key | specifies key information for use in |
logging | specifies what the server logs, and where |
lwres | configures named to |
masters | defines a named masters list for |
options | controls global server configuration |
server | sets certain configuration options on |
trusted-keys | defines trusted DNSSEC keys. |
view | defines a view. |
zone | defines a zone. |
The logging and
options statements may only occur once per
configuration.
The acl statement assigns a symbolic
name to an address match list. It gets its name from a primary
use of address match lists: Access Control Lists (ACLs).
Note that an address match list's name must be defined
with acl before it can be used elsewhere; no
forward references are allowed.
The following ACLs are built-in:
any | Matches all hosts. |
none | Matches no hosts. |
localhost | Matches the IPv4 and IPv6 addresses of all network |
localnets | Matches any host on an IPv4 or IPv6 network |
controls {
inet ( ip_addr | * ) [ port ip_port ] allow { address_match_list }
keys { key_list };
[ inet ...; ]
};
The controls statement declares control
channels to be used by system administrators to control the
operation of the name server. These control channels are
used by the rndc utility to send commands to
and retrieve non-DNS results from a name server.
An inet control channel is a TCP
socket listening at the specified
ip_port on the specified
ip_addr, which can be an IPv4 or IPv6
address. An ip_addr
of * is interpreted as the IPv4 wildcard
address; connections will be accepted on any of the system's
IPv4 addresses. To listen on the IPv6 wildcard address,
use an ip_addr of ::.
If you will only use rndc on the local host,
using the loopback address (127.0.0.1
or ::1) is recommended for maximum
security.
If no port is specified, port 953
is used. "*" cannot be used for
ip_port.
The ability to issue commands over the control channel is
restricted by the allow and
keys clauses. Connections to the control
channel are permitted based on the
address_match_list. This is for simple
IP address based filtering only; any key_id
elements of the address_match_list are
ignored.
The primary authorization mechanism of the command
channel is the key_list, which contains
a list of key_ids.
Each key_id in
the key_list is authorized to execute
commands over the control channel.
See Remote Name Daemon Control application in
the section called “Administrative Tools”) for information about
configuring keys in rndc.
If no controls statement is present,
named will set up a default
control channel listening on the loopback address 127.0.0.1
and its IPv6 counterpart ::1.
In this case, and also when the controls statement
is present but does not have a keys clause,
named will attempt to load the command channel key
from the file rndc.key in/etc (or whatever sysconfdir
was specified as when BIND was built).
To create a rndc.key file, runrndc-confgen -a.
The rndc.key feature was created to
ease the transition of systems from BIND 8,
which did not have digital signatures on its command channel messages
and thus did not have a keys clause.
It makes it possible to use an existing BIND 8
configuration file in BIND 9 unchanged,
and still have rndc work the same way
ndc worked in BIND 8, simply by executing the
command rndc-confgen -a after BIND 9 is
installed.
Since the rndc.key feature
is only intended to allow the backward-compatible usage of
BIND 8 configuration files, this feature does not
have a high degree of configurability. You cannot easily change
the key name or the size of the secret, so you should make a
rndc.conf with your own key if you wish to change
those things. The rndc.key file also has its
permissions set such that only the owner of the file (the user that
named is running as) can access it. If you
desire greater flexibility in allowing other users to access
rndc commands then you need to create an
rndc.conf and make it group readable by a group
that contains the users who should have access.
The UNIX control channel type of BIND 8 is not supported
in BIND 9, and is not expected to be added in future
releases. If it is present in the controls statement from a
BIND 8 configuration file, it is ignored
and a warning is logged.
To disable the command channel, use an empty controls
statement: controls { };.
The include statement inserts the
specified file at the point where the include
statement is encountered. The include
statement facilitates the administration of configuration files
by permitting the reading or writing of some things but not
others. For example, the statement could include private keys
that are readable only by the name server.
The key statement defines a shared
secret key for use with TSIG (see the section called “TSIG”)
or the command channel
(see the section called “controls Statement Definition and Usage”).
The key statement can occur at the top level
of the configuration file or inside a view
statement. Keys defined in top-level key
statements can be used in all views. Keys intended for use in
a controls statement
(see the section called “controls Statement Definition and Usage”)
must be defined at the top level.
The key_id, also known as the
key name, is a domain name uniquely identifying the key. It can
be used in a server
statement to cause requests sent to that
server to be signed with this key, or in address match lists to
verify that incoming requests have been signed with a key
matching this name, algorithm, and secret.
The algorithm_id is a string
that specifies a security/authentication algorithm. The only
algorithm currently supported with TSIG authentication ishmac-md5. Thesecret_string is the secret to be
used by the algorithm, and is treated as a base-64 encoded
string.
logging {
[ channel channel_name {
( file path name
[ versions ( number | unlimited ) ]
[ size size spec ]
| syslog syslog_facility
| stderr
| 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 ; ... ]
}; ]
...
};
The logging statement configures a wide
variety of logging options for the name server. Its channel phrase
associates output methods, format options and severity levels with
a name that can then be used with the category phrase
to select how various classes of messages are logged.
Only one logging statement is used to define
as many channels and categories as are wanted. If there is no logging statement,
the logging configuration will be:
logging {
category default { default_syslog; default_debug; };
category unmatched { null; };
};
In BIND 9, the logging configuration is only established when
the entire configuration file has been parsed. In BIND 8, it was
established as soon as the logging statement
was parsed. When the server is starting up, all logging messages
regarding syntax errors in the configuration file go to the default
channels, or to standard error if the "-g" option
was specified.
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 destination clause that
says whether messages selected for the channel go to a file, to a
particular syslog facility, to the standard error stream, or are
discarded. It can optionally also limit the message severity level
that will be accepted by the channel (the default is
info), and whether to include a
named-generated time stamp, the category name
and/or severity level (the default is not to include any).
The null destination clause
causes all messages sent to the channel to be discarded;
in that case, other options for the channel are meaningless.
The file destination clause directs the channel
to a disk file. It can include limitations
both on how large the file is allowed to become, and how many versions
of the file will be saved each time the file is opened.
If you use the versions log file 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 openedlamers.log.1 is renamed tolamers.log.2, lamers.log.0 is renamed
to lamers.log.1, and lamers.log is
renamed to lamers.log.0.
You can say versions unlimited to not limit
the number of versions.
If a size option is associated with the log file,
then renaming is only done when the file being opened exceeds the
indicated size. No backup versions are kept by default; any existing
log file is simply appended.
The size option for files is used to limit log
growth. If the file ever exceeds the size, then named will
stop writing to the file unless it has a versions option
associated with it. If backup versions are kept, the files are rolled as
described above and a new one begun. If there is no
versions option, no more data will be written to the log
until some out-of-band mechanism removes or truncates the log to less than the
maximum size. The default behavior is not to limit the size of the
file.
Example usage of the size and
versions options:
channel an_example_channel {
file "example.log" versions 3 size 20m;
print-time yes;
print-category yes;
};
The syslog destination clause directs the
channel to the system log. Its argument is a
syslog facility as described in the syslog man
page. Known facilities are kern, user,
mail, daemon, auth,
syslog, lpr, news,
uucp, cron, authpriv,
ftp, local0, local1,
local2, local3, local4,
local5, local6 and
local7, however not all facilities are supported on
all operating systems.
How syslog will handle messages sent to
this facility is described in the syslog.conf man
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 stderr destination clause directs the
channel to the server's standard error stream. This is intended for
use when the server is running as a foreground process, for example
when debugging a configuration.
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 running rndc trace.
The global debug level
can be set to zero, and debugging mode turned off, by running ndc
notrace. All debugging messages in the server have a debug
level, and higher debug levels give more detailed output. Channels
that specify a specific debug severity, for example:
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 debug 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-Feb-2000 15:05:32.863 general: notice: running
There are four predefined channels that are used for
named's default logging as follows. How they are
used is described in the section called “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 {
stderr; // writes to stderr
severity info; // only send priority info
// and higher
};
channel null {
null; // toss anything sent to
// this channel
};
The default_debug channel has the special
property that it only produces output when the server's debug level is
nonzero. It normally writes to a file named.run
in the server's working directory.
For security reasons, when the "-u"
command line option is used, the named.run file
is created only after named has changed to the
new UID, and any debug output generated while named is
starting up and still running as root is discarded. If you need
to capture this output, you must run the server with the "-g"
option and redirect standard error to a file.
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.
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 xfer-out { null; };
category notify { null; };
Following are the available categories and brief descriptions
of the types of log information they contain. More
categories may be added in future BIND releases.
default | The default category defines the logging |
general | The catch-all. Many things still aren't |
database | Messages relating to the databases used |
security | Approval and denial of requests. |
config | Configuration file parsing and processing. |
resolver | DNS resolution, such as the recursive |
xfer-in | Zone transfers the server is receiving. |
xfer-out | Zone transfers the server is sending. |
notify | The NOTIFY protocol. |
client | Processing of client requests. |
unmatched | Messages that named was unable to determine the |
network | Network operations. |
update | Dynamic updates. |
update-security | Approval and denial of update requests. |
queries | Specify where queries should be logged to.
|
dispatch | Dispatching of incoming packets to the |
dnssec | DNSSEC and TSIG protocol processing. |
lame-servers | Lame servers. These are misconfigurations |
delegation-only | Delegation only. Logs queries that have have |
This is the grammar of the lwres
statement in the named.conf file:
lwres {
[ listen-on { ip_addr [port ip_port] ; [ ip_addr [port ip_port] ; ... ] }; ]
[ view view_name; ]
[ search { domain_name ; [ domain_name ; ... ] }; ]
[ ndots number; ]
};
The lwres statement configures the name
server to also act as a lightweight resolver server, see
the section called “Running a Resolver Daemon”. There may be be multiple
lwres statements configuring
lightweight resolver servers with different properties.
The listen-on statement specifies a list of
addresses (and ports) that this instance of a lightweight resolver daemon
should accept requests on. If no port is specified, port 921 is used.
If this statement is omitted, requests will be accepted on 127.0.0.1,
port 921.
The view statement binds this instance of a
lightweight resolver daemon to a view in the DNS namespace, so that the
response will be constructed in the same manner as a normal DNS query
matching this view. If this statement is omitted, the default view is
used, and if there is no default view, an error is triggered.
The search statement is equivalent to the
search statement in/etc/resolv.conf. It provides a list of domains
which are appended to relative names in queries.
The ndots statement is equivalent to the
ndots statement in/etc/resolv.conf. It indicates the minimum
number of dots in a relative domain name that should result in an
exact match lookup before search path elements are appended.
mastersname[portip_port] { (masters_list|ip_addr[portip_port] [keykey] ) ; [...] } ;
masters lists allow for a common set of masters
to be easily used by multiple stub and slave zones.
This is the grammar of the options
statement in the named.conf file:
options {
[ version version_string; ]
[ hostname hostname_string; ]
[ server-id server_id_string; ]
[ directory path_name; ]
[ key-directory path_name; ]
[ named-xfer path_name; ]
[ tkey-domain domainname; ]
[ tkey-dhkey key_name key_tag; ]
[ dump-file path_name; ]
[ memstatistics-file path_name; ]
[ pid-file path_name; ]
[ statistics-file path_name; ]
[ zone-statistics yes_or_no; ]
[ auth-nxdomain yes_or_no; ]
[ deallocate-on-exit yes_or_no; ]
[ dialup dialup_option; ]
[ fake-iquery yes_or_no; ]
[ fetch-glue yes_or_no; ]
[ flush-zones-on-shutdown yes_or_no; ]
[ has-old-clients yes_or_no; ]
[ host-statistics yes_or_no; ]
[ host-statistics-max number; ]
[ minimal-responses yes_or_no; ]
[ multiple-cnames yes_or_no; ]
[ notify yes_or_no | explicit; ]
[ recursion yes_or_no; ]
[ rfc2308-type1 yes_or_no; ]
[ use-id-pool yes_or_no; ]
[ maintain-ixfr-base yes_or_no; ]
[ dnssec-enable yes_or_no; ]
[ dnssec-lookaside domain trust-anchor domain; ]
[ dnssec-must-be-secure domain yes_or_no; ]
[ forward ( only | first ); ]
[ forwarders { [ ip_addr [port ip_port] ; ... ] }; ]
[ dual-stack-servers [port ip_port] { ( domain_name [port ip_port] | ip_addr [port ip_port] ) ; ... }; ]
[ check-names ( master | slave | response )( warn | fail | ignore ); ]
[ allow-notify { address_match_list }; ]
[ allow-query { address_match_list }; ]
[ allow-transfer { address_match_list }; ]
[ allow-recursion { address_match_list }; ]
[ allow-update-forwarding { address_match_list }; ]
[ allow-v6-synthesis { address_match_list }; ]
[ blackhole { address_match_list }; ]
[ avoid-v4-udp-ports { port_list }; ]
[ avoid-v6-udp-ports { port_list }; ]
[ listen-on [ port ip_port ] { address_match_list }; ]
[ listen-on-v6 [ port ip_port ] { address_match_list }; ]
[ query-source [ address ( ip_addr | * ) ] [ port ( ip_port | * ) ]; ]
[ query-source-v6 [ address ( ip_addr | * ) ] [ port ( ip_port | * ) ]; ]
[ max-transfer-time-in number; ]
[ max-transfer-time-out number; ]
[ max-transfer-idle-in number; ]
[ max-transfer-idle-out number; ]
[ tcp-clients number; ]
[ recursive-clients number; ]
[ serial-query-rate number; ]
[ serial-queries number; ]
[ tcp-listen-queue number; ]
[ transfer-format ( one-answer | many-answers ); ]
[ transfers-in number; ]
[ transfers-out number; ]
[ transfers-per-ns number; ]
[ transfer-source (ip4_addr | *) [port ip_port] ; ]
[ transfer-source-v6 (ip6_addr | *) [port ip_port] ; ]
[ alt-transfer-source (ip4_addr | *) [port ip_port] ; ]
[ alt-transfer-source-v6 (ip6_addr | *) [port ip_port] ; ]
[ use-alt-transfer-source yes_or_no; ]
[ notify-source (ip4_addr | *) [port ip_port] ; ]
[ notify-source-v6 (ip6_addr | *) [port ip_port] ; ]
[ also-notify { ip_addr [port ip_port] ; [ ip_addr [port ip_port] ; ... ] }; ]
[ max-ixfr-log-size number; ]
[ max-journal-size size_spec; ]
[ 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 ; ... ] ] };
[ lame-ttl number; ]
[ max-ncache-ttl number; ]
[ max-cache-ttl number; ]
[ sig-validity-interval number ; ]
[ min-roots number; ]
[ use-ixfr yes_or_no ; ]
[ provide-ixfr yes_or_no; ]
[ request-ixfr yes_or_no; ]
[ treat-cr-as-space yes_or_no ; ]
[ min-refresh-time number ; ]
[ max-refresh-time number ; ]
[ min-retry-time number ; ]
[ max-retry-time number ; ]
[ port ip_port; ]
[ additional-from-auth yes_or_no ; ]
[ additional-from-cache yes_or_no ; ]
[ random-device path_name ; ]
[ max-cache-size size_spec ; ]
[ match-mapped-addresses yes_or_no; ]
[ preferred-glue ( A | AAAA | NONE ); ]
[ edns-udp-size number; ]
[ root-delegation-only [ exclude { namelist } ] ; ]
[ querylog yes_or_no ; ]
[ disable-algorithms domain { algorithm; [ algorithm; ] }; ]
};
The options statement sets up global options
to be used by BIND. This statement may appear only
once in a configuration file. If there is no options
statement, an options block with each option set to its default will
be used.
- 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.- key-directory
When performing dynamic update of secure zones, the
directory where the public and private key files should be found,
if different than the current working directory. The directory specified
must be an absolute path.- named-xfer
This option is obsolete.
It was used in BIND 8 to
specify the pathname to the named-xfer program.
In BIND 9, no separate named-xfer program is
needed; its functionality is built into the name server.- tkey-domain
The domain appended to the names of all
shared keys generated with TKEY. When a client
requests a TKEY exchange, it may or may not specify
the desired name for the key. If present, the name of the shared
key will be "client specified part" +
"tkey-domain".
Otherwise, the name of the shared key will be "random hex" + "
digitstkey-domain". In most cases,
the domainname should be the server's domain
name.- tkey-dhkey
The Diffie-Hellman key used by the server
to generate shared keys with clients using the Diffie-Hellman mode
of TKEY. The server must be able to load the
public and private keys from files in the working directory. In
most cases, the keyname should be the server's host name.- dump-file
The pathname of the file the server dumps
the database to when instructed to do so with
rndc dumpdb.
If not specified, the default isnamed_dump.db.- memstatistics-file
The pathname of the file the server writes memory
usage statistics to on exit. If not specified,
the default isnamed.memstats.- pid-file
The pathname of the file the server writes its process ID
in. If not specified, the default is/var/run/named.pid.
The pid-file is used by programs that want to send signals to the running
name server. Specifying pid-file none disables the
use of a PID file — no file will be written and any
existing one will be removed. Note that none
is a keyword, not a file name, and therefore is not enclosed in
double quotes.- statistics-file
The pathname of the file the server appends statistics
to when instructed to do so using rndc stats.
If not specified, the default isnamed.statsin the
server's current directory. The format of the file is described
in the section called “The Statistics File”- port
The UDP/TCP port number the server uses for
receiving and sending DNS protocol traffic.
The default is 53. This option is mainly intended for server testing;
a server using a port other than 53 will not be able to communicate with
the global DNS.- random-device
The source of entropy to be used by the server. Entropy is primarily needed
for DNSSEC operations, such as TKEY transactions and dynamic update of signed
zones. This options specifies the device (or file) from which to read
entropy. If this is a file, operations requiring entropy will fail when the
file has been exhausted. If not specified, the default value is/dev/random
(or equivalent) when present, and none otherwise. The
random-device option takes effect during
the initial configuration load at server startup time and
is ignored on subsequent reloads.- preferred-glue
If specified the listed type (A or AAAA) will be emitted before other glue
in the additional section of a query response.
The default is not to preference any type (NONE).- root-delegation-only
Turn on enforcement of delegation-only in TLDs and root zones with an optional
exclude list.
Note some TLDs are NOT delegation only (e.g. "DE", "LV", "US" and "MUSEUM").
options {
root-delegation-only exclude { "de"; "lv"; "us"; "museum"; };
};- disable-algorithms
Disable the specified DNSSEC algorithms at and below the specified name.
Multiple disable-algorithms statements are allowed.
Only the most specific will be applied.- dnssec-lookaside
When set dnssec-lookaside provides the
validator with an alternate method to validate DNSKEY records at the
top of a zone. When a DNSKEY is at or below a domain specified by the
deepest dnssec-lookaside, and the normal dnssec validation
has left the key untrusted, the trust-anchor will be append to the key
name and a DLV record will be looked up to see if it can validate the
key. If the DLV record validates a DNSKEY (similarly to the way a DS
record does) the DNSKEY RRset is deemed to be trusted.- dnssec-must-be-secure
Specify heirarchies which must / may not be secure (signed and validated).
Ifyesthen named will only accept answers if they
are secure.
Ifnothen normal dnssec validation applies
allowing for insecure answers to be accepted.
The specified domain must be under a trusted-key or
dnssec-lookaside must be active.
- auth-nxdomain
If
yes, then the AA bit
is always set on NXDOMAIN responses, even if the server is not actually
authoritative. The default isno; this is
a change from BIND 8. If you are using very old DNS software, you
may need to set it toyes.- deallocate-on-exit
This option was used in BIND 8 to enable checking
for memory leaks on exit. BIND 9 ignores the option and always performs
the checks.- 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 isno.The dialup option
may also be specified in the view and
zone statements,
in which case it overrides the global dialup
option.If the zone is a master zone then the server will send out a NOTIFY
request to all the slaves (default). This should trigger the zone serial
number check in the slave (providing it supports NOTIFY) allowing the slave
to verify the zone while the connection is active.
The set of servers to which NOTIFY is sent can be controlled by
notify and also-notify.If the
zone is a slave or stub zone, then the server will suppress the regular
"zone up to date" (refresh) queries and only perform them when the
heartbeat-interval expires in addition to sending
NOTIFY requests.Finer control can be achieved by using
notifywhich only sends NOTIFY messages,notify-passivewhich sends NOTIFY messages and
suppresses the normal refresh queries,refresh
which suppresses normal refresh processing and sends refresh queries
when the heartbeat-interval expires, andpassivewhich just disables normal refresh
processing.dialup mode
normal refresh
heart-beat refresh
heart-beat notify
no (default)
yes
no
no
yes
no
yes
yes
notify
yes
no
yes
refresh
no
yes
no
passive
no
no
no
notify-passive
no
no
yes
Note that normal NOTIFY processing is not affected by
dialup.- fake-iquery
In BIND 8, this option
enabled simulating the obsolete DNS query type
IQUERY. BIND 9 never does IQUERY simulation.- fetch-glue
This option is obsolete.
In BIND 8,fetch-glue yes
caused the server to attempt to fetch glue resource records it
didn't have when constructing the additional
data section of a response. This is now considered a bad idea
and BIND 9 never does it.- flush-zones-on-shutdown
When the nameserver exits due receiving SIGTERM,
flush / do not flush any pending zone writes. The default is
flush-zones-on-shutdownno.- has-old-clients
This option was incorrectly implemented
in BIND 8, and is ignored by BIND 9.
To achieve the intended effect
of
has-old-clientsyes, specify
the two separate options auth-nxdomainyes
and rfc2308-type1noinstead.- host-statistics
In BIND 8, this enables keeping of
statistics for every host that the name server interacts with.
Not implemented in BIND 9.- maintain-ixfr-base
This option is obsolete.
It was used in BIND 8 to determine whether a transaction log was
kept for Incremental Zone Transfer. BIND 9 maintains a transaction
log whenever possible. If you need to disable outgoing incremental zone
transfers, use provide-ixfrno.- minimal-responses
If
yes, then when generating
responses the server will only add records to the authority and
additional data sections when they are required (e.g. delegations,
negative responses). This may improve the performance of the server.
The default isno.- multiple-cnames
This option was used in BIND 8 to allow
a domain name to have multiple CNAME records in violation of the
DNS standards. BIND 9.2 always strictly
enforces the CNAME rules both in master files and dynamic updates.- notify
If
yes(the default),
DNS NOTIFY messages are sent when a zone the server is authoritative for
changes, see the section called “Notify”. The messages are sent to the
servers listed in the zone's NS records (except the master server identified
in the SOA MNAME field), and to any servers listed in the
also-notify option.
Ifexplicit, notifies are sent only to
servers explicitly listed using also-notify.
Ifno, no notifies are sent.
The notify option may also be
specified in the zone statement,
in which case it overrides the options notify statement.
It would only be necessary to turn off this option if it caused slaves
to crash.- 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 off
and the server does not already know the answer, it will return a
referral response. The default isyes.
Note that setting recursion no does not prevent
clients from getting data from the server's cache; it only
prevents new data from being cached as an effect of client queries.
Caching may still occur as an effect the server's internal
operation, such as NOTIFY address lookups.
See also fetch-glue above.- rfc2308-type1
Setting this to
yeswill
cause the server to send NS records along with the SOA record for negative
answers. The default isno.Note
Not yet implemented in BIND 9.
- use-id-pool
This option is obsolete.
BIND 9 always allocates query IDs from a pool.- zone-statistics
If
yes, the server will collect
statistical data on all zones (unless specifically turned off
on a per-zone basis by specifying zone-statistics no
in the zone statement). These statistics may be accessed
using rndc stats, which will dump them to the file listed
in the statistics-file. See also the section called “The Statistics File”.- use-ixfr
This option is obsolete.
If you need to disable IXFR to a particular server or servers see
the information on the provide-ixfr option
in the section called “server Statement Definition and Usage”. See also
the section called “Incremental Zone Transfers (IXFR)”.- provide-ixfr
See the description of
provide-ixfr in
the section called “server Statement Definition and Usage”- request-ixfr
See the description of
request-ixfr in
the section called “server Statement Definition and Usage”- treat-cr-as-space
This option was used in BIND 8 to make
the server treat carriage return ("\r") characters the same way
as a space or tab character,
to facilitate loading of zone files on a UNIX system that were generated
on an NT or DOS machine. In BIND 9, both UNIX "\n"
and NT/DOS "\r\n" newlines are always accepted,
and the option is ignored.
additional-from-auth, additional-from-cache
These options control the behavior of an authoritative server when
answering queries which have additional data, or when following CNAME
and DNAME chains.
When both of these options are set toyes
(the default) and a
query is being answered from authoritative data (a zone
configured into the server), the additional data section of the
reply will be filled in using data from other authoritative zones
and from the cache. In some situations this is undesirable, such
as when there is concern over the correctness of the cache, or
in servers where slave zones may be added and modified by
untrusted third parties. Also, avoiding
the search for this additional data will speed up server operations
at the possible expense of additional queries to resolve what would
otherwise be provided in the additional section.
For example, if a query asks for an MX record for hostfoo.example.com,
and the record found is "MX 10 mail.example.net", normally the address
records (A and AAAA) formail.example.netwill be provided as well,
if known, even though they are not in the example.com zone.
Setting these options to no disables this behavior and makes
the server only search for additional data in the zone it answers from.
These options are intended for use in authoritative-only
servers, or in authoritative-only views. Attempts to set
them to no without also specifying
recursion no will cause the server to
ignore the options and log a warning message.
Specifying additional-from-cache no actually
disables the use of the cache not only for additional data lookups
but also when looking up the answer. This is usually the desired
behavior in an authoritative-only server where the correctness of
the cached data is an issue.
When a name server is non-recursively queried for a name that is not
below the apex of any served zone, it normally answers with an
"upwards referral" to the root servers or the servers of some other
known parent of the query name. Since the data in an upwards referral
comes from the cache, the server will not be able to provide upwards
referrals when additional-from-cache no
has been specified. Instead, it will respond to such queries
with REFUSED. This should not cause any problems since
upwards referrals are not required for the resolution process.- match-mapped-addresses
If
yes, then an
IPv4-mapped IPv6 address will match any address match
list entries that match the corresponding IPv4 address.
Enabling this option is sometimes useful on IPv6-enabled Linux
systems, to work around a kernel quirk that causes IPv4
TCP connections such as zone transfers to be accepted
on an IPv6 socket using mapped addresses, causing
address match lists designed for IPv4 to fail to match.
The use of this option for any other purpose is discouraged.- ixfr-from-differences
When 'yes' and the server loads a new version of a master
zone from its zone file or receives a new version of a slave
file by a non-incremental zone transfer, it will compare
the new version to the previous one and calculate a set
of differences. The differences are then logged in the
zone's journal file such that the changes can be transmitted
to downstream slaves as an incremental zone transfer.
By allowing incremental zone transfers to be used for
non-dynamic zones, this option saves bandwidth at the
expense of increased CPU and memory consumption at the master.
In particular, if the new version of a zone is completely
different from the previous one, the set of differences
will be of a size comparable to the combined size of the
old and new zone version, and the server will need to
temporarily allocate memory to hold this complete
difference set.- multi-master
This should be set when you have multiple masters for a zone and the
addresses refer to different machines. If 'yes' named will not log
when the serial number on the master is less than what named currently
has. The default isno.- dnssec-enable
Enable DNSSEC support in named. Unless set toyes
named behaves as if it does not support DNSSEC.
The default isno.- querylog
Specify whether query logging should be started when named start.
If querylog is not specified then the query logging
is determined by the presence of the logging category queries.- check-names
This option is used to restrict the character set and syntax of
certain domain names in master files and/or DNS responses received
from the network. The default varies according to usage area. For
master zones the default is fail.
For slave zones the default is warn.
For answer received from the network (response)
the default is ignore.The rules for legal hostnames / mail domains are derived from RFC 952
and RFC 821 as modified by RFC 1123.check-names applies to the owner names of A, AAA and
MX records. It also applies to the domain names in the RDATA of NS, SOA and MX
records. It also applies to the RDATA of PTR records where the owner name
indicated that it is a reverse lookup of a hostname (the owner name ends in
IN-ADDR.ARPA, IP6.ARPA, IP6.INT).
The forwarding facility can be used to create a large site-wide
cache on a few servers, reducing traffic over links to external
name servers. It can also be used to allow queries by servers that
do not have direct access to the Internet, but wish to look up exterior
names anyway. Forwarding occurs only on those queries for which
the server is not authoritative and does not have the answer in
its cache.
- forward
This option is only meaningful if the
forwarders list is not empty. A value offirst,
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. Ifonlyis 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-domain basis, allowing
for the global forwarding options to be overridden in a variety
of ways. You can set particular domains to use different forwarders,
or have a different forward only/first behavior,
or not forward at all, see the section called “zone
Statement Grammar”.
Dual-stack servers are used as servers of last resort to work around
problems in reachability due the lack of support for either IPv4 or IPv6
on the host machine.
- dual-stack-servers
Specifies host names / addresses of machines with access to
both IPv4 and IPv6 transports. If a hostname is used the server must be able
to resolve the name using only the transport it has. If the machine is dual
stacked then the dual-stack-servers have no effect unless
access to a transport has been disabled on the command line
(e.g. named -4).
Access to the server can be restricted based on the IP address
of the requesting system. See the section called “Address Match Lists” for
details on how to specify IP address lists.
- allow-notify
Specifies which hosts are allowed to
notify this server, a slave, of zone changes in addition
to the zone masters.
allow-notify may also be specified in the
zone statement, in which case it overrides the
options allow-notify statement. It is only meaningful
for a slave zone. If not specified, the default is to process notify messages
only from a zone's master.- allow-query
Specifies which hosts are allowed to
ask ordinary DNS questions. allow-query may also
be specified in the zone statement, in which
case it overrides the options allow-query statement. If
not specified, the default is to allow queries from all hosts.- allow-recursion
Specifies which hosts are allowed to
make recursive queries through this server. If not specified, the
default is to allow recursive queries from all hosts.
Note that disallowing recursive queries for a host does not prevent the
host from retrieving data that is already in the server's cache.- allow-update-forwarding
Specifies which hosts are allowed to
submit Dynamic DNS updates to slave zones to be forwarded to the
master. The default is{ none; }, which
means that no update forwarding will be performed. To enable
update forwarding, specifyallow-update-forwarding { any; };.
Specifying values other than{ none; }or{ any; }is usually counterproductive, since
the responsibility for update access control should rest with the
master server, not the slaves.Note that enabling the update forwarding feature on a slave server
may expose master servers relying on insecure IP address based
access control to attacks; see the section called “Dynamic Update Security”
for more details.- allow-v6-synthesis
This option was introduced for the smooth transition from AAAA
to A6 and from "nibble labels" to binary labels.
However, since both A6 and binary labels were then deprecated,
this option was also deprecated.
It is now ignored with some warning messages.- 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 to 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. The default isnone.
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 name server on port 53 for the IP address
5.6.7.8, and on port 1234 of an address on the machine in net
1.2 that is not 1.2.3.4.
If no listen-on is specified, the
server will listen on port 53 on all interfaces.
The listen-on-v6 option is used to
specify the interfaces and the ports on which the server will listen
for incoming queries sent using IPv6.
When
{ any; } is specified
as the address_match_list for the
listen-on-v6 option,
the server does not bind a separate socket to each IPv6 interface
address as it does for IPv4 if the operating system has enough API
support for IPv6 (specifically if it conforms to RFC 3493 and RFC 3542).
Instead, it listens on the IPv6 wildcard address.
If the system only has incomplete API support for IPv6, however,
the behavior is the same as that for IPv4.
A list of particular IPv6 addresses can also be specified, in which case
the server listens on a separate socket for each specified address,
regardless of whether the desired API is supported by the system.
Multiple listen-on-v6 options can be used.
For example,
listen-on-v6 { any; };
listen-on-v6 port 1234 { !2001:db8::/32; any; };
will enable the name server on port 53 for any IPv6 addresses
(with a single wildcard socket),
and on port 1234 of IPv6 addresses that is not in the prefix
2001:db8::/32 (with separate sockets for each matched address.)
To make the server not listen on any IPv6 address, use
listen-on-v6 { none; };
If no listen-on-v6 option is specified,
the server will not listen on any IPv6 address.
If the server doesn't know the answer to a question, it will
query other name servers. query-source specifies
the address and port used for such queries. For queries sent over
IPv6, there is a separate query-source-v6 option.
If address is * 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, avoid-v4-udp-ports
and avoid-v6-udp-ports can be used to prevent named
from selecting certain ports. The defaults are
query-source address * port *;
query-source-v6 address * port *;
Note
The address specified in the query-source option
is used for both UDP and TCP queries, but the port applies only to
UDP queries. TCP queries always use a random
unprivileged port.
Note
See also transfer-source and
notify-source.
BIND has mechanisms in place to facilitate zone transfers
and set limits on the amount of load that transfers place on the
system. The following options apply to zone transfers.
- also-notify
Defines a global list of IP addresses of name servers
that are also sent NOTIFY messages whenever a fresh copy of the
zone is loaded, in addition to the servers listed in the zone's NS records.
This helps to ensure that copies of the zones will
quickly converge on stealth servers. 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 be sent NOTIFY messages for that zone. The default is the empty
list (no global notification list).- max-transfer-time-in
Inbound zone transfers running longer than
this many minutes will be terminated. The default is 120 minutes
(2 hours). The maximum value is 28 days (40320 minutes).- max-transfer-idle-in
Inbound zone transfers making no progress
in this many minutes will be terminated. The default is 60 minutes
(1 hour). The maximum value is 28 days (40320 minutes).- max-transfer-time-out
Outbound zone transfers running longer than
this many minutes will be terminated. The default is 120 minutes
(2 hours). The maximum value is 28 days (40320 minutes).- max-transfer-idle-out
Outbound zone transfers making no progress
in this many minutes will be terminated. The default is 60 minutes (1
hour). The maximum value is 28 days (40320 minutes).- serial-query-rate
Slave servers will periodically query master servers
to find out if zone serial numbers have changed. Each such query uses
a minute amount of the slave server's network bandwidth. To limit the
amount of bandwidth used, BIND 9 limits the rate at which queries are
sent. The value of the serial-query-rate option,
an integer, is the maximum number of queries sent per second.
The default is 20.- serial-queries
In BIND 8, the serial-queries option
set the maximum number of concurrent serial number queries
allowed to be outstanding at any given time.
BIND 9 does not limit the number of outstanding
serial queries and ignores the serial-queries option.
Instead, it limits the rate at which the queries are sent
as defined using the serial-query-rate option.- transfer-format
Zone transfers can be sent using two different formats,
one-answer and many-answers.
The transfer-format option is used
on the master server to determine which format it sends.
one-answer uses one DNS message per
resource record transferred.
many-answers packs as many resource records as
possible into a message. many-answers is more
efficient, but is only supported by relatively new slave servers,
such as BIND 9, BIND 8.x and patched
versions of BIND 4.9.5. The default is
many-answers. 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 is10.
Increasing transfers-in may speed up the convergence
of slave zones, but it also may increase the load on the local system.- transfers-out
The maximum number of outbound zone transfers
that can be running concurrently. Zone transfer requests in excess
of the limit will be refused. The default value is10.- transfers-per-ns
The maximum number of inbound zone transfers
that can be concurrently transferring from a given remote name server.
The default value is2. Increasing transfers-per-ns may
speed up the convergence of slave zones, but it also may increase
the load on the remote name server. transfers-per-ns may
be overridden on a per-server basis by using the transfers phrase
of the server statement.- transfer-source
transfer-source determines
which local address will be bound to IPv4 TCP connections used to
fetch zones transferred inbound by the server. It also determines
the source IPv4 address, and optionally the UDP port, used for the
refresh queries and forwarded dynamic updates. If not set, it defaults
to a system controlled value which will usually be the address of
the interface "closest to" the remote end. This address must appear
in the remote end's allow-transfer option for
the zone being transferred, if one is specified. This statement
sets the transfer-source for all zones, but can
be overridden on a per-view or per-zone basis by including a
transfer-source statement within the
view or zone block
in the configuration file.- transfer-source-v6
The same as transfer-source,
except zone transfers are performed using IPv6.- alt-transfer-source
An alternate transfer source if the one listed in
transfer-source fails and
use-alt-transfer-source is
set.
Note
If you do not wish the alternate transfer source
to be used you should set
use-alt-transfer-source
appropriately and you should not depend upon
getting a answer back to the first refresh
query.
- alt-transfer-source-v6
An alternate transfer source if the one listed in
transfer-source-v6 fails and
use-alt-transfer-source is set.- use-alt-transfer-source
Use the alternate transfer sources or not. If views are
specified this defaults to no otherwise it defaults to
yes (for BIND 8 compatibility).- notify-source
notify-source determines
which local source address, and optionally UDP port, will be used to
send NOTIFY messages.
This address must appear in the slave server's masters
zone clause or in an allow-notify clause.
This statement sets the notify-source for all zones,
but can be overridden on a per-zone / per-view basis by including a
notify-source statement within the zone
or view block in the configuration file.- notify-source-v6
Like notify-source,
but applies to notify messages sent to IPv6 addresses.
avoid-v4-udp-ports and avoid-v6-udp-ports
specify a list of IPv4 and IPv6 UDP ports that will not be used as system
assigned source ports for UDP sockets. These lists prevent named
from choosing as its random source port a port that is blocked by
your firewall. If a query went out with such a source port, the
answer would not get by the firewall and the name server would have
to query again.
The server's usage of many system resources can be limited.
Scaled values are allowed when specifying resource limits. For
example, 1G can be used instead of
1073741824 to specify a limit of one
gigabyte. unlimited requests unlimited use, or the
maximum available amount. default uses the limit
that was in force when the server was started. See the description of
size_spec in the section called “Configuration File Elements”.
The following options set operating system resource limits for
the name server process. Some operating systems don't support some or
any of the limits. On such systems, a warning will be issued if the
unsupported limit is used.
- coresize
The maximum size of a core dump. The default
isdefault.- datasize
The maximum amount of data memory the server
may use. The default isdefault.
This is a hard limit on server memory usage.
If the server attempts to allocate memory in excess of this
limit, the allocation will fail, which may in turn leave
the server unable to perform DNS service. Therefore,
this option is rarely useful as a way of limiting the
amount of memory used by the server, but it can be used
to raise an operating system data size limit that is
too small by default. If you wish to limit the amount
of memory used by the server, use the
max-cache-size and
recursive-clients
options instead.- files
The maximum number of files the server
may have open concurrently. The default isunlimited.- stacksize
The maximum amount of stack memory the server
may use. The default isdefault.
The following options set limits on the server's
resource consumption that are enforced internally by the
server rather than the operating system.
- max-ixfr-log-size
This option is obsolete; it is accepted
and ignored for BIND 8 compatibility. The option
max-journal-size performs a similar
function in BIND 8.- max-journal-size
Sets a maximum size for each journal file
(the section called “The journal file”). When the journal file approaches
the specified size, some of the oldest transactions in the journal
will be automatically removed. The default isunlimited.- host-statistics-max
In BIND 8, specifies the maximum number of host statistic
entries to be kept.
Not implemented in BIND 9.- recursive-clients
The maximum number of simultaneous recursive lookups
the server will perform on behalf of clients. The default is1000. Because each recursing client uses a fair
bit of memory, on the order of 20 kilobytes, the value of the
recursive-clients option may have to be decreased
on hosts with limited memory.- tcp-clients
The maximum number of simultaneous client TCP
connections that the server will accept.
The default is100.- max-cache-size
The maximum amount of memory to use for the
server's cache, in bytes. When the amount of data in the cache
reaches this limit, the server will cause records to expire
prematurely so that the limit is not exceeded. In a server with
multiple views, the limit applies separately to the cache of each
view. The default isunlimited, meaning that
records are purged from the cache only when their TTLs expire.- tcp-listen-queue
The listen queue depth. The default and minimum is 3.
If the kernel supports the accept filter "dataready" this also controls how
many TCP connections that will be queued in kernel space waiting for
some data before being passed to accept. Values less than 3 will be
silently raised.
- cleaning-interval
The server will remove expired resource records
from the cache every cleaning-interval minutes.
The default is 60 minutes. The maximum value is 28 days (40320 minutes).
If set to 0, no periodic cleaning will occur.- heartbeat-interval
The server will perform zone maintenance tasks
for all zones marked as dialup whenever this
interval expires. The default is 60 minutes. Reasonable values are up
to 1 day (1440 minutes). The maximum value is 28 days (40320 minutes).
If set to 0, no zone maintenance for these zones will occur.- interface-interval
The server will scan the network interface list
every interface-interval minutes. The default
is 60 minutes. The maximum value is 28 days (40320 minutes).
If set to 0, interface scanning will only occur when
the configuration file is loaded. After the scan, the server will
begin listening for queries on any newly discovered
interfaces (provided they are allowed by the
listen-on configuration), and will
stop listening on interfaces that have gone away.- statistics-interval
Name server statistics will be logged
every statistics-interval minutes. The default is
60. The maximum value is 28 days (40320 minutes).
If set to 0, no statistics will be logged.Note
Not yet implemented in BIND9.
All other things being equal, when the server chooses a name server
to query from a list of name servers, 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 non-negated 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; };
Note
The topology option
is not implemented in BIND 9.
The response to a DNS query may consist of multiple resource
records (RRs) forming a resource records set (RRset).
The name server will normally return the
RRs within the RRset in an indeterminate order
(but see the rrset-order
statement in the section called “RRset Ordering”).
The client resolver code should rearrange the RRs as appropriate,
that is, using any addresses on the local net in preference to other addresses.
However, not all resolvers can do this or are correctly configured.
When a client is using a local server the sorting can be performed
in the server, based on the client's address. This only requires
configuring the name servers, not all the clients.
The sortlist statement (see below) takes
an address_match_list and interprets it even
more specifically than the topology statement
does (the section called “Topology”).
Each top level statement in the sortlist must
itself be an explicit address_match_list with
one or two elements. The first element (which may be an IP address,
an IP prefix, an ACL name or a nested address_match_list)
of each top level list is checked against the source address of
the query until a match is found.
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 the same as 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 behavior 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; };
};
When multiple records are returned in an answer it may be
useful to configure the order of the records placed into the response.
The rrset-order statement permits configuration
of the ordering of the records in a multiple record response.
See also the sortlist statement,
the section called “The sortlist Statement”.
An order_spec is defined as follows:
[ classclass_name][ typetype_name][ name"domain_name"]
orderordering
If no class is specified, the default is ANY.
If no type 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 |
random | Records are returned in some random order. |
cyclic | Records are returned in a round-robin |
For example:
rrset-order {
class IN type A name "host.example.com" order random;
order cyclic;
};
will cause any responses for type A records in class IN that
have "host.example.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.
Note
The rrset-order statement
is not yet fully implemented in BIND 9.
BIND 9 currently does not support "fixed" ordering.
- lame-ttl
Sets the number of seconds to cache a
lame server indication. 0 disables caching. (This is
NOT recommended.)
Default is600(10 minutes). Maximum value is1800(30 minutes).- max-ncache-ttl
To reduce network traffic and increase performance
the server stores negative answers. max-ncache-ttl is
used to set a maximum retention time for these answers in the server
in seconds. The default
max-ncache-ttl is10800seconds (3 hours).
max-ncache-ttl cannot exceed 7 days and will
be silently truncated to 7 days if set to a greater value.- max-cache-ttl
max-cache-ttl sets
the maximum time for which the server will cache ordinary (positive)
answers. The default is one week (7 days).- min-roots
The minimum number of root servers that
is required for a request for the root servers to be accepted. Default
is2.Note
Not implemented in BIND9.
- sig-validity-interval
Specifies the number of days into the
future when DNSSEC signatures automatically generated as a result
of dynamic updates (the section called “Dynamic Update”)
will expire. The default is30days.
The maximum value is 10 years (3660 days). The signature
inception time is unconditionally set to one hour before the current time
to allow for a limited amount of clock skew.
min-refresh-time, max-refresh-time, min-retry-time, max-retry-time
These options control the server's behavior on refreshing a zone
(querying for SOA changes) or retrying failed transfers.
Usually the SOA values for the zone are used, but these values
are set by the master, giving slave server administrators little
control over their contents.
These options allow the administrator to set a minimum and maximum
refresh and retry time either per-zone, per-view, or globally.
These options are valid for slave and stub zones,
and clamp the SOA refresh and retry times to the specified values.- edns-udp-size
edns-udp-size sets the advertised EDNS UDP buffer
size. Valid values are 512 to 4096 (values outside this range will be
silently adjusted). The default value is 4096. The usual reason for
setting edns-udp-size to a non default value it to get UDP answers to
pass through broken firewalls that block fragmented packets and/or
block UDP packets that are greater than 512 bytes.
The server provides some helpful diagnostic information
through a number of built-in zones under the
pseudo-top-level-domain bind in the
CHAOS class. These zones are part of a
built-in view (see the section called “view Statement Grammar”) of class
CHAOS which is separate from the default view of
class IN; therefore, any global server options
such as allow-query do not apply the these zones.
If you feel the need to disable these zones, use the options
below, or hide the built-in CHAOS view by
defining an explicit view of class CHAOS
that matches all clients.
- version
The version the server should report
via a query of the nameversion.bind
with type TXT, class CHAOS.
The default is the real version number of this server.
Specifying version none
disables processing of the queries.- hostname
The hostname the server should report via a query of
the namehostname.bind
with type TXT, class CHAOS.
This defaults to the hostname of the machine hosting the name server as
found by gethostname(). The primary purpose of such queries is to
identify which of a group of anycast servers is actually
answering your queries. Specifying hostname none;
disables processing of the queries.- server-id
The ID of the server should report via a query of
the nameID.SERVER
with type TXT, class CHAOS.
The primary purpose of such queries is to
identify which of a group of anycast servers is actually
answering your queries. Specifying server-id none;
disables processing of the queries.
Specifying server-id hostname; will cause named to
use the hostname as found by gethostname().
The default server-id is none.
The statistics file generated by BIND 9
is similar, but not identical, to that
generated by BIND 8.
The statistics dump begins with the line +++ Statistics Dump
+++ (973798949), where the number in parentheses is a standard
Unix-style timestamp, measured as seconds since January 1, 1970. Following
that line are a series of lines containing a counter type, the value of the
counter, optionally a zone name, and optionally a view name.
The lines without view and zone listed are global statistics for the entire server.
Lines with a zone and view name for the given view and zone (the view name is
omitted for the default view). The statistics dump ends
with the line --- Statistics Dump --- (973798949), where the
number is identical to the number in the beginning line.
The following statistics counters are maintained:
success | The number of |
referral | The number of queries which resulted |
nxrrset | The number of queries which resulted in |
nxdomain | The number |
failure | The number of queries which resulted in a |
recursion | The number of queries which caused the server |
Each query received by the server will cause exactly one of
success,
referral,
nxrrset,
nxdomain, or
failure
to be incremented, and may additionally cause the
recursion counter to be incremented.
serverip_addr{
[ bogusyes_or_no; ]
[ provide-ixfryes_or_no; ]
[ request-ixfryes_or_no; ]
[ ednsyes_or_no; ]
[ transfersnumber; ]
[ transfer-format( one-answer | many-answers ); ]]
[ keys{ string ; [ string ; [...]] }; ]
[ transfer-source (ip4_addr|*) [portip_port] ; ]
[ transfer-source-v6 (ip6_addr|*) [portip_port] ; ]
};
The server statement defines characteristics
to be associated with a remote name server.
The server statement can occur at the top level of the
configuration file or inside a view statement.
If a view statement contains
one or more server statements, only those
apply to the view and any top-level ones are ignored.
If a view contains no server statements,
any top-level server statements are used as
defaults.
If you discover that a remote server is giving out bad data,
marking it as bogus will prevent further queries to it. The default
value of bogus is no.
The provide-ixfr clause determines whether
the local server, acting as master, will respond with an incremental
zone transfer when the given remote server, a slave, requests it.
If set to yes, incremental transfer will be provided
whenever possible. If set to no, all transfers
to the remote server will be non-incremental. If not set, the value
of the provide-ixfr option in the view or
global options block is used as a default.
The request-ixfr clause determines whether
the local server, acting as a slave, will request incremental zone
transfers from the given remote server, a master. If not set, the
value of the request-ixfr option in the view or
global options block is used as a default.
IXFR requests to servers that do not support IXFR will automatically
fall back to AXFR. Therefore, there is no need to manually list
which servers support IXFR and which ones do not; the global default
of yes should always work.
The purpose of the provide-ixfr and
request-ixfr clauses is
to make it possible to disable the use of IXFR even when both master
and slave claim to support it, for example if one of the servers
is buggy and crashes or corrupts data when IXFR is used.
The edns clause determines whether the local server
will attempt to use EDNS when communicating with the remote server. The
default is yes.
The server supports two zone transfer methods. The first, one-answer,
uses one DNS message per resource record transferred. many-answers packs
as many resource records as possible into a message. many-answers is
more efficient, but is only known to be understood by BIND 9, BIND
8.x, and patched versions of BIND 4.9.5. You can specify which method
to use for a server with the transfer-format option.
If transfer-format is not specified, the transfer-format specified
by the options statement will be used.
transfers is used to limit the number of
concurrent inbound zone transfers from the specified server. If
no transfers clause is specified, the limit is
set according to the transfers-per-ns option.
The keys clause identifies a
key_id defined by the key statement,
to be used for transaction security (TSIG, the section called “TSIG”)
when talking to the remote server.
When a request is sent to the remote server, a request signature
will be generated using the key specified here and appended to the
message. A request originating from the remote server is not required
to be signed by this key.
Although the grammar of the keys clause
allows for multiple keys, only a single key per server is currently
supported.
The transfer-source and
transfer-source-v6 clauses specify the IPv4 and IPv6 source
address to be used for zone transfer with the remote server, respectively.
For an IPv4 remote server, only transfer-source can
be specified.
Similarly, for an IPv6 remote server, only
transfer-source-v6 can be specified.
Form more details, see the description of
transfer-source and
transfer-source-v6 in
the section called “Zone Transfers”.
trusted-keys {
string number number number string ;
[ string number number number string ; [...]]
};
The trusted-keys statement defines DNSSEC
security roots. DNSSEC is described in the section called “DNSSEC”. A security root is defined when the public key for a non-authoritative
zone is known, but cannot be securely obtained through DNS, either
because it is the DNS root zone or because its parent zone is unsigned.
Once a key has been configured as a trusted key, it is treated as
if it had been validated and proven secure. The resolver attempts
DNSSEC validation on all DNS data in subdomains of a security root.
The trusted-keys statement can contain
multiple key entries, each consisting of the key's domain name,
flags, protocol, algorithm, and the base-64 representation of the
key data.
viewview_name
[class] {
match-clients {address_match_list} ;
match-destinations {address_match_list} ;
match-recursive-onlyyes_or_no;
[view_option; ...]
[zone_statement; ...]
};
The view statement is a powerful new feature
of BIND 9 that lets a name server answer a DNS query differently
depending on who is asking. It is particularly useful for implementing
split DNS setups without having to run multiple servers.
Each view statement defines a view of the
DNS namespace that will be seen by a subset of clients. A client matches
a view if its source IP address matches theaddress_match_list of the view's
match-clients clause and its destination IP address matches
the address_match_list of the view's
match-destinations clause. If not specified, both
match-clients and match-destinations
default to matching all addresses. In addition to checking IP addresses
match-clients and match-destinations
can also take keys which provide an mechanism for the
client to select the view. A view can also be specified
as match-recursive-only, which means that only recursive
requests from matching clients will match that view.
The order of the view statements is significant —
a client request will be resolved in the context of the first
view that it matches.
Zones defined within a view statement will
be only be accessible to clients that match the view.
By defining a zone of the same name in multiple views, different
zone data can be given to different clients, for example, "internal"
and "external" clients in a split DNS setup.
Many of the options given in the options statement
can also be used within a view statement, and then
apply only when resolving queries with that view. When no view-specific
value is given, the value in the options statement
is used as a default. Also, zone options can have default values specified
in the view statement; these view-specific defaults
take precedence over those in the options statement.
Views are class specific. If no class is given, class IN
is assumed. Note that all non-IN views must contain a hint zone,
since only the IN class has compiled-in default hints.
If there are no view statements in the config
file, a default view that matches any client is automatically created
in class IN. Any zone statements specified on
the top level of the configuration file are considered to be part of
this default view, and the options statement will
apply to the default view. If any explicit view
statements are present, all zone statements must
occur inside view statements.
Here is an example of a typical split DNS setup implemented
using view statements.
view "internal" {
// This should match our internal networks.
match-clients { 10.0.0.0/8; };
// Provide recursive service to internal clients only.
recursion yes;
// Provide a complete view of the example.com zone
// including addresses of internal hosts.
zone "example.com" {
type master;
file "example-internal.db";
};
};
view "external" {
// Match all clients not matched by the previous view.
match-clients { any; };
// Refuse recursive service to external clients.
recursion no;
// Provide a restricted view of the example.com zone
// containing only publicly accessible hosts.
zone "example.com" {
type master;
file "example-external.db";
};
};
zonezone_name[class] [{
type ( master | slave | hint | stub | forward | delegation-only ) ;
[ allow-notify {address_match_list} ; ]
[ allow-query {address_match_list} ; ]
[ allow-transfer {address_match_list} ; ]
[ allow-update {address_match_list} ; ]
[ update-policy {update_policy_rule[...] } ; ]
[ allow-update-forwarding {address_match_list} ; ]
[ also-notify {ip_addr[portip_port] ; [ip_addr[portip_port] ; ... ] }; ]
[ check-names (warn|fail|ignore) ; ]
[ dialupdialup_option; ]
[ delegation-onlyyes_or_no; ]
[ filestring; ]
[ forward (only|first) ; ]
[ forwarders { [ip_addr[portip_port] ; ... ] }; ]
[ ixfr-basestring; ]
[ ixfr-tmp-filestring; ]
[ maintain-ixfr-baseyes_or_no; ]
[ masters [portip_port] { (masters_list|ip_addr[portip_port] [keykey] ) ; [...] } ; ]
[ max-ixfr-log-sizenumber; ]
[ max-transfer-idle-innumber; ]
[ max-transfer-idle-outnumber; ]
[ max-transfer-time-innumber; ]
[ max-transfer-time-outnumber; ]
[ notifyyes_or_no|explicit; ]
[ pubkeynumbernumbernumberstring; ]
[ transfer-source (ip4_addr|*) [portip_port] ; ]
[ transfer-source-v6 (ip6_addr|*) [portip_port] ; ]
[ alt-transfer-source (ip4_addr|*) [portip_port] ; ]
[ alt-transfer-source-v6 (ip6_addr|*) [portip_port] ; ]
[ use-alt-transfer-sourceyes_or_no; ]
[ notify-source (ip4_addr|*) [portip_port] ; ]
[ notify-source-v6 (ip6_addr|*) [portip_port] ; ]
[ zone-statisticsyes_or_no; ]
[ sig-validity-intervalnumber; ]
[ databasestring; ]
[ min-refresh-timenumber; ]
[ max-refresh-timenumber; ]
[ min-retry-timenumber; ]
[ max-retry-timenumber; ]
[ multi-masteryes_or_no; ]
[ key-directorypath_name; ]
}];
| The server has a master copy of the data |
| A slave zone is a replica of a master |
| A stub zone is similar to a slave zone, Stub zones can be used to eliminate the need for glue NS record Stub zones can also be used as a way of forcing the resolution |
| A "forward zone" is a way to configure |
| The initial set of root name servers is |
| This is used to enforce the delegation only
|
The zone's name may optionally be followed by a class. If
a class is not specified, class IN (for Internet),
is assumed. This is correct for the vast majority of cases.
The hesiod class is
named for an information service from MIT's Project Athena. It is
used to share information about various systems databases, such
as users, groups, printers and so on. The keywordHS is
a synonym for hesiod.
Another MIT development is CHAOSnet, a LAN protocol created
in the mid-1970s. Zone data for it can be specified with the CHAOS class.
- allow-notify
See the description of
allow-notify in the section called “Access Control”- allow-query
See the description of
allow-query in the section called “Access Control”- allow-transfer
See the description of allow-transfer
in the section called “Access Control”.- allow-update
Specifies which hosts are allowed to
submit Dynamic DNS updates for master zones. The default is to deny
updates from all hosts. Note that allowing updates based
on the requestor's IP address is insecure; see
the section called “Dynamic Update Security” for details.- update-policy
Specifies a "Simple Secure Update" policy. See
the section called “Dynamic Update Policies”.- allow-update-forwarding
See the description of allow-update-forwarding
in the section called “Access Control”.- also-notify
Only meaningful if notify is
active for this zone. The set of machines that will receive aDNS NOTIFYmessage
for this zone is made up of all the listed name servers (other than
the primary master) for the zone plus any IP addresses specified
with also-notify. A port may be specified
with each also-notify address to send the notify
messages to a port other than the default of 53.
also-notify is not meaningful for stub zones.
The default is the empty list.- check-names
This option is used to restrict the character set and syntax of
certain domain names in master files and/or DNS responses received from the
network. The default varies according to zone type. For master zones the default is fail. For slave
zones the default is warn.- database
Specify the type of database to be used for storing the
zone data. The string following the database keyword
is interpreted as a list of whitespace-delimited words. The first word
identifies the database type, and any subsequent words are passed
as arguments to the database to be interpreted in a way specific
to the database type.The default is
"rbt", BIND 9's native in-memory
red-black-tree database. This database does not take arguments.Other values are possible if additional database drivers
have been linked into the server. Some sample drivers are included
with the distribution but none are linked in by default.- dialup
See the description of
dialup in the section called “Boolean Options”.- delegation-only
The flag only applies to hint and stub zones. If set
toyesthen the zone will also be treated as if it
is also a delegation-only type zone.- forward
Only meaningful if the zone has a forwarders
list. The only value causes the lookup to fail
after trying the forwarders and getting no answer, while first would
allow a normal lookup to be tried.- forwarders
Used to override the list of global forwarders.
If it is not specified in a zone of type forward,
no forwarding is done for the zone; the global options are not used.- ixfr-base
Was used in BIND 8 to specify the name
of the transaction log (journal) file for dynamic update and IXFR.
BIND 9 ignores the option and constructs the name of the journal
file by appending ".jnl" to the name of the
zone file.- ixfr-tmp-file
Was an undocumented option in BIND 8.
Ignored in BIND 9.- max-transfer-time-in
See the description of
max-transfer-time-in in the section called “Zone Transfers”.- max-transfer-idle-in
See the description of
max-transfer-idle-in in the section called “Zone Transfers”.- max-transfer-time-out
See the description of
max-transfer-time-out in the section called “Zone Transfers”.- max-transfer-idle-out
See the description of
max-transfer-idle-out in the section called “Zone Transfers”.- notify
See the description of
notify in the section called “Boolean Options”.- pubkey
In BIND 8, this option was intended for specifying
a public zone key for verification of signatures in DNSSEC signed
zones when they are loaded from disk. BIND 9 does not verify signatures
on load and ignores the option.- zone-statistics
If
yes, the server will keep statistical
information for this zone, which can be dumped to the
statistics-file defined in the server options.- sig-validity-interval
See the description of
sig-validity-interval in the section called “Tuning”.- transfer-source
See the description of
transfer-source in the section called “Zone Transfers”- transfer-source-v6
See the description of
transfer-source-v6 in the section called “Zone Transfers”- alt-transfer-source
See the description of
alt-transfer-source in the section called “Zone Transfers”- alt-transfer-source-v6
See the description of
alt-transfer-source-v6 in the section called “Zone Transfers”- use-alt-transfer-source
See the description of
use-alt-transfer-source in the section called “Zone Transfers”- notify-source
See the description of
notify-source in the section called “Zone Transfers”- notify-source-v6
See the description of
notify-source-v6 in the section called “Zone Transfers”.
min-refresh-time, max-refresh-time, min-retry-time, max-retry-time
See the description in the section called “Tuning”.- ixfr-from-differences
See the description of
ixfr-from-differences in the section called “Boolean Options”.- key-directory
See the description of
key-directory in the section called “options Statement Definition and Usage”- multi-master
See the description of
multi-master in the section called “Boolean Options”.
BIND 9 supports two alternative methods of granting clients
the right to perform dynamic updates to a zone,
configured by the allow-update and
update-policy option, respectively.
The allow-update clause works the same
way as in previous versions of BIND. It grants given clients the
permission to update any record of any name in the zone.
The update-policy clause is new in BIND
9 and allows more fine-grained control over what updates are allowed.
A set of rules is specified, where each rule either grants or denies
permissions for one or more names to be updated by one or more identities.
If the dynamic update request message is signed (that is, it includes
either a TSIG or SIG(0) record), the identity of the signer can
be determined.
Rules are specified in the update-policy zone
option, and are only meaningful for master zones. When the update-policy statement
is present, it is a configuration error for the allow-update statement
to be present. The update-policy statement only
examines the signer of a message; the source address is not relevant.
This is how a rule definition looks:
( grant | deny )identitynametypename[types]
Each rule grants or denies privileges. Once a message has
successfully matched a rule, the operation is immediately granted
or denied and no further rules are examined. A rule is matched
when the signer matches the identity field, the name matches the
name field in accordance with the nametype field, and the type matches
the types specified in the type field.
The identity field specifies a name or a wildcard name. Normally, this
is the name of the TSIG or SIG(0) key used to sign the update request. When a
TKEY exchange has been used to create a shared secret, the identity of the
shared secret is the same as the identity of the key used to authenticate the
TKEY exchange. When the identity field specifies a
wildcard name, it is subject to DNS wildcard expansion, so the rule will apply
to multiple identities. The identity field must
contain a fully qualified domain name.
The nametype field has 4 values:name, subdomain,wildcard, and self.
| Exact-match semantics. This rule matches when the |
| This rule matches when the name being updated |
| The |
| This rule matches when the name being updated |
In all cases, the name field must
specify a fully qualified domain name.
If no types are explicitly specified, this rule matches all types except
SIG, NS, SOA, and NXT. Types may be specified by name, including
"ANY" (ANY matches all types except NXT, which can never be updated).
Note that when an attempt is made to delete all records associated with a
name, the rules are checked for each existing record type.
This section, largely borrowed from RFC 1034, describes the
concept of a Resource Record (RR) and explains when each is used.
Since the publication of RFC 1034, several new RRs have been identified
and implemented in the DNS. These are also included.
A domain name identifies a node. Each node has a set of
resource information, which may be empty. The set of resource
information associated with a particular name is composed of
separate RRs. The order of RRs in a set is not significant and
need not be preserved by name servers, resolvers, or other
parts of the DNS. However, sorting of multiple RRs is
permitted for optimization purposes, for example, to specify
that a particular nearby server be tried first. See the section called “The sortlist Statement” and the section called “RRset Ordering”.
The components of a Resource Record are:
owner name | the domain name where the RR is found. |
type | an encoded 16 bit value that specifies |
TTL | the time to live of the RR. This field |
class | an encoded 16 bit value that identifies |
RDATA | the resource data. The format of the |
The following are types of valid RRs:
A | a host address. In the IN class, this is a |
AAAA | IPv6 address. Described in RFC 1886. |
A6 | IPv6 address. This can be a partial |
AFSDB | location of AFS database servers. |
APL | address prefix list. Experimental. |
CERT | holds a digital certificate. |
CNAME | identifies the canonical name of an alias. |
DNAME | Replaces the domain name specified with |
GPOS | Specifies the global position. Superseded by LOC. |
HINFO | identifies the CPU and OS used by a host. |
ISDN | representation of ISDN addresses. |
KEY | stores a public key associated with a |
KX | identifies a key exchanger for this |
LOC | for storing GPS info. Described in RFC 1876. |
MX | identifies a mail exchange for the domain. |
NAPTR | name authority pointer. Described in RFC 2915. |
NSAP | a network service access point. |
NS | the authoritative name server for the |
NXT | used in DNSSEC to securely indicate that |
PTR | a pointer to another part of the domain |
PX | provides mappings between RFC 822 and X.400 |
RP | information on persons responsible |
RT | route-through binding for hosts that |
SIG | ("signature") contains data authenticated |
SOA | identifies the start of a zone of authority. |
SRV | information about well known network |
TXT | text records. Described in RFC 1035. |
WKS | information about which well known |
X25 | representation of X.25 network addresses. |
The following classes of resource records
are currently valid in the DNS:
IN | The Internet. |
CH |
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The owner name is often implicit, rather than forming an integral
part of the RR. For example, many name servers internally form tree
or hash structures for the name space, and chain RRs off nodes.
The remaining RR parts are the fixed header (type, class, TTL)
which is consistent for all RRs, and a variable part (RDATA) that
fits the needs of the resource being described.
The meaning of the TTL field is a time limit on how long an
RR can be kept in a cache. This limit does not apply to authoritative
data in zones; it is also timed out, but by the refreshing policies
for the zone. The TTL is assigned by the administrator for the
zone where the data originates. While short TTLs can be used to
minimize caching, and a zero TTL prohibits caching, the realities
of Internet performance suggest that these times should be on the
order of days for the typical host. If a change can be anticipated,
the TTL can be reduced prior to the change to minimize inconsistency
during the change, and then increased back to its former value following
the change.
The data in the RDATA section of RRs is carried as a combination
of binary strings and domain names. The domain names are frequently
used as "pointers" to other data in the DNS.
RRs are represented in binary form in the packets of the DNS
protocol, and are usually represented in highly encoded form when
stored in a name server or resolver. In the examples provided in
RFC 1034, a style similar to that used in master files was employed
in order to show the contents of RRs. In this format, most RRs
are shown on a single line, although continuation lines are possible
using parentheses.
The start of the line gives the owner of the RR. If a line
begins with a blank, then the owner is assumed to be the same as
that of the previous RR. Blank lines are often included for readability.
Following the owner, we list the TTL, type, and class of the
RR. Class and type use the mnemonics defined above, and TTL is
an integer before the type field. In order to avoid ambiguity in
parsing, type and class mnemonics are disjoint, TTLs are integers,
and the type mnemonic is always last. The IN class and TTL values
are often omitted from examples in the interests of clarity.
The resource data or RDATA section of the RR are given using
knowledge of the typical representation for the data.
For example, we might show the RRs carried in a message as:
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The MX RRs have an RDATA section which consists of a 16 bit
number followed by a domain name. The address RRs use a standard
IP address format to contain a 32 bit internet address.
This example shows six RRs, with two RRs at each of three
domain names.
Similarly we might see:
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This example shows two addresses for XX.LCS.MIT.EDU,
each of a different class.
As described above, domain servers store information as a
series of resource records, each of which contains a particular
piece of information about a given domain name (which is usually,
but not always, a host). The simplest way to think of a RR is as
a typed pair of data, a domain name matched with a relevant datum,
and stored with some additional type information to help systems
determine when the RR is relevant.
MX records are used to control delivery of email. The data
specified in the record is a priority and a domain name. The priority
controls the order in which email delivery is attempted, with the
lowest number first. If two priorities are the same, a server is
chosen randomly. If no servers at a given priority are responding,
the mail transport agent will fall back to the next largest priority.
Priority numbers do not have any absolute meaning — they are relevant
only respective to other MX records for that domain name. The domain
name given is the machine to which the mail will be delivered. It must have
an associated A record — CNAME is not sufficient.
For a given domain, if there is both a CNAME record and an
MX record, the MX record is in error, and will be ignored. Instead,
the mail will be delivered to the server specified in the MX record
pointed to by the CNAME.
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For example:
Mail delivery will be attempted to mail.example.com andmail2.example.com (in
any order), and if neither of those succeed, delivery to mail.backup.org will
be attempted.
The time to live of the RR field is a 32 bit integer represented
in units of seconds, and is primarily used by resolvers when they
cache RRs. The TTL describes how long a RR can be cached before it
should be discarded. The following three types of TTL are currently
used in a zone file.
SOA | The last field in the SOA is the negative The maximum time for |
$TTL | The $TTL directive at the top of the |
RR TTLs | Each RR can have a TTL as the second |
All of these TTLs default to units of seconds, though units
can be explicitly specified, for example, 1h30m.
Reverse name resolution (that is, translation from IP address
to name) is achieved by means of the in-addr.arpa domain
and PTR records. Entries in the in-addr.arpa domain are made in
least-to-most significant order, read left to right. This is the
opposite order to the way IP addresses are usually written. Thus,
a machine with an IP address of 10.1.2.3 would have a corresponding
in-addr.arpa name of
3.2.1.10.in-addr.arpa. This name should have a PTR resource record
whose data field is the name of the machine or, optionally, multiple
PTR records if the machine has more than one name. For example,
in the [example.com] domain:
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Note
The $ORIGIN lines in the examples
are for providing context to the examples only-they do not necessarily
appear in the actual usage. They are only used here to indicate
that the example is relative to the listed origin.
The Master File Format was initially defined in RFC 1035 and
has subsequently been extended. While the Master File Format itself
is class independent all records in a Master File must be of the same
class.
Master File Directives include $ORIGIN, $INCLUDE,
and $TTL.
Syntax: $ORIGINdomain-name [ comment]
$ORIGIN sets the domain name that will
be appended to any unqualified records. When a zone is first read
in there is an implicit $ORIGIN <zone-name>. The
current $ORIGIN is appended to the domain specified
in the $ORIGIN argument if it is not absolute.
$ORIGIN example.com.
WWW CNAME MAIN-SERVER
is equivalent to
WWW.EXAMPLE.COM. CNAME MAIN-SERVER.EXAMPLE.COM.
Syntax: $INCLUDEfilename [origin ] [ comment ]
Read and process the file filename as
if it were included into the file at this point. If origin is
specified the file is processed with $ORIGIN set
to that value, otherwise the current $ORIGIN is
used.
The origin and the current domain name
revert to the values they had prior to the $INCLUDE once
the file has been read.
Note
RFC 1035 specifies that the current origin should be restored after
an $INCLUDE, but it is silent on whether the current
domain name should also be restored. BIND 9 restores both of them.
This could be construed as a deviation from RFC 1035, a feature, or both.
Syntax: $TTLdefault-ttl [comment ]
Set the default Time To Live (TTL) for subsequent records
with undefined TTLs. Valid TTLs are of the range 0-2147483647 seconds.
$TTL is defined in RFC 2308.
Syntax: $GENERATE range lhs [ttl] [class] type rhs [ comment ]
$GENERATE is used to create a series of
resource records that only differ from each other by an iterator. $GENERATE can
be used to easily generate the sets of records required to support
sub /24 reverse delegations described in RFC 2317: Classless IN-ADDR.ARPA
delegation.
$ORIGIN 0.0.192.IN-ADDR.ARPA.
$GENERATE 1-2 0 NS SERVER$.EXAMPLE.
$GENERATE 1-127 $ CNAME $.0
is equivalent to
0.0.0.192.IN-ADDR.ARPA NS SERVER1.EXAMPLE.
0.0.0.192.IN-ADDR.ARPA. NS SERVER2.EXAMPLE.
1.0.0.192.IN-ADDR.ARPA. CNAME 1.0.0.0.192.IN-ADDR.ARPA.
2.0.0.192.IN-ADDR.ARPA. CNAME 2.0.0.0.192.IN-ADDR.ARPA.
...
127.0.0.192.IN-ADDR.ARPA. CNAME 127.0.0.0.192.IN-ADDR.ARPA.
range | This can be one of two forms: start-stop |
lhs | lhs describes the For compatibility with earlier versions $$ is still |
ttl | ttl specifies the class and ttl can be |
class | class specifies the class and ttl can be |
type | At present the only supported types are |
rhs | rhs is a domain name. It is processed |
The $GENERATE directive is a BIND extension
and not part of the standard zone file format.
BIND 8 does not support the optional TTL and CLASS fields.
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