Saturday, January 21, 2006

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 script
contrib/named-bootconf/named-bootconf.sh.




Configuration File Elements



Following is a list of elements used throughout the BIND configuration
file documentation:

















































































acl_name

The name of an address_match_list as
defined by the acl statement.

address_match_list

A list of one or more ip_addr,
ip_prefix, key_id,
or acl_name elements, see
the section called “Address Match Lists”.

domain_name

A quoted string which will be used as
a DNS name, for example "my.test.domain".

dotted_decimal

One to four integers valued 0 through
255 separated by dots (`.'), such as 123,
45.67 or 89.123.45.67.

ip4_addr

An IPv4 address with exactly four elements
in dotted_decimal notation.

ip6_addr

An IPv6 address, such as 2001:db8::1234.
IPv6 scoped addresses that have ambiguity on their scope zones must be
disambiguated by an appropriate zone ID with the percent character
(`%') as delimiter.
It is strongly recommended to use string zone names rather than
numeric identifiers, in order to be robust against system
configuration changes.
However, since there is no standard mapping for such names and
identifier values, currently only interface names as link identifiers
are supported, assuming one-to-one mapping between interfaces and links.
For example, a link-local address fe80::1 on the
link attached to the interface ne0

can be specified as fe80::1%ne0.
Note that on most systems link-local addresses always have the
ambiguity, and need to be disambiguated.

ip_addr

An ip4_addr or ip6_addr.

ip_port

An IP port number.
number is limited to 0 through 65535, with values
below 1024 typically restricted to use by processes running as root.
In some cases an asterisk (`*') character can be used as a placeholder to
select a random high-numbered port.

ip_prefix

An IP network specified as an ip_addr,
followed by a slash (`/') and then the number of bits in the netmask.
Trailing zeros in a ip_addr may omitted.
For example, 127/8 is the network 127.0.0.0 with
netmask 255.0.0.0 and 1.2.3.0/28 is
network 1.2.3.0 with netmask 255.255.255.240.

key_id

A domain_name representing
the name of a shared key, to be used for transaction security.

key_list

A list of one or more key_ids,
separated by semicolons and ending with a semicolon.

number

A non-negative 32 bit integer
(i.e., a number between 0 and 4294967295, inclusive).
Its acceptable value might further
be limited by the context in which it is used.

path_name

A quoted string which will be used as
a pathname, such as zones/master/my.test.domain.

size_spec


A number, the word unlimited,
or the word default.



An unlimited size_spec requests unlimited
use, or the maximum available amount. A default size_spec uses
the limit that was in force when the server was started.



A number can
optionally be followed by a scaling factor: K or k for
kilobytes, M or m for
megabytes, and G or g for gigabytes,
which scale by 1024, 1024*1024, and 1024*1024*1024 respectively.



The value must be representable as a 64-bit unsigned integer
(0 to 18446744073709551615, inclusive).
Using unlimited is the best way
to safely set a really large number.


yes_or_no

Either yes or no.
The words true and false are
also accepted, as are the numbers 1 and 0.

dialup_option

One of yes,
no, notify,
notify-passive, refresh or
passive.
When used in a zone, notify-passive,

refresh, and passive
are restricted to slave and stub zones.




Address Match Lists




Syntax



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 } )





Definition and Usage


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.







Comment Syntax


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.




Syntax



/* 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







Definition and Usage


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.








Configuration File Grammar


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
matching list, for access control and other uses.

controls

declares control channels to be used
by the rndc utility.

include

includes a file.

key

specifies key information for use in
authentication and authorization using TSIG.

logging

specifies what the server logs, and where
the log messages are sent.

lwres

configures named to
also act as a light weight resolver daemon (lwresd).

masters

defines a named masters list for
inclusion in stub and slave zone masters clauses.

options

controls global server configuration
options and sets defaults for other statements.

server

sets certain configuration options on
a per-server basis.

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.




acl Statement Grammar



acl acl-name {
address_match_list
};




acl Statement Definition and
Usage


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
interfaces on the system.

localnets

Matches any host on an IPv4 or IPv6 network
for which the system has an interface.
Some systems do not provide a way to determine the prefix lengths of
local IPv6 addresses.
In such a case, localnets only matches the local
IPv6 addresses, just like localhost.





controls Statement Grammar


controls {
inet ( ip_addr | * ) [ port ip_port ] allow { address_match_list }
keys { key_list };
[ inet ...; ]
};





controls Statement Definition and Usage


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, run
rndc-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 { };.





include Statement Grammar


include filename;




include Statement Definition and Usage



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.





key Statement Grammar



key key_id {
algorithm string;
secret string;
};




key Statement Definition and Usage


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 is
hmac-md5. The
secret_string is the secret to be
used by the algorithm, and is treated as a base-64 encoded
string.






logging Statement Grammar


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 ; ... ]
}; ]
...
};





logging Statement Definition and Usage


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.





The channel Phrase


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 opened

lamers.log.1 is renamed to
lamers.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.





The category Phrase


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
options for those categories where no specific configuration has been
defined.

general

The catch-all. Many things still aren't
classified into categories, and they all end up here.

database

Messages relating to the databases used
internally by the name server to store zone and cache data.

security

Approval and denial of requests.

config

Configuration file parsing and processing.

resolver

DNS resolution, such as the recursive
lookups performed on behalf of clients by a caching name server.

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
class of or for which there was no matching view.
A one line summary is also logged to the client category.
This category is best sent to a file or stderr, by default it is sent to
the null channel.

network

Network operations.

update

Dynamic updates.

update-security

Approval and denial of update requests.

queries


Specify where queries should be logged to.



At startup, specifing the category queries will also
enable query logging unless querylog option has been
specified.




The query log entry reports the client's IP address and port number. The
query name, class and type. It also reports whether the Recursion Desired
flag was set (+ if set, - if not set), EDNS was in use (E) or if the
query was signed (S).


client 127.0.0.1#62536: query: www.example.com IN AAAA +SE


client ::1#62537: query: www.example.net IN AAAA -SE


dispatch

Dispatching of incoming packets to the
server modules where they are to be processed.

dnssec

DNSSEC and TSIG protocol processing.

lame-servers

Lame servers. These are misconfigurations
in remote servers, discovered by BIND 9 when trying to query
those servers during resolution.

delegation-only

Delegation only. Logs queries that have have
been forced to NXDOMAIN as the result of a delegation-only zone or
a delegation-only in a hint or stub zone declaration.






lwres Statement Grammar


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; ]
};





lwres Statement Definition and Usage


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.





masters Statement Grammar




masters name [port ip_port] { ( masters_list | ip_addr [port ip_port] [key key] ) ; [...] } ;





masters Statement Definition and Usage


masters lists allow for a common set of masters
to be easily used by multiple stub and slave zones.





options Statement Grammar



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; ] }; ]
};





options Statement Definition and Usage


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
digits
" + "tkey-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 is named_dump.db.


memstatistics-file

The pathname of the file the server writes memory
usage statistics to on exit. If not specified,
the default is named.memstats.



pid-file

The pathname of the file the server writes its process ID
in. If not specified, the default is /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 is named.stats in 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).
If yes then named will only accept answers if they
are secure.
If no then 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.






Boolean Options



auth-nxdomain

If yes, then the AA bit
is always set on NXDOMAIN responses, even if the server is not actually
authoritative. The default is no; this is
a change from BIND 8. If you are using very old DNS software, you
may need to set it to yes.



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 is no.



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
notify which only sends NOTIFY messages,
notify-passive which sends NOTIFY messages and
suppresses the normal refresh queries, refresh
which suppresses normal refresh processing and sends refresh queries
when the heartbeat-interval expires, and

passive which 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-shutdown no.


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-clients yes, specify
the two separate options auth-nxdomain yes
and rfc2308-type1 no instead.


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-ixfr no.



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 is no.


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.



If explicit, notifies are sent only to
servers explicitly listed using also-notify.
If no, 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 is yes.
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 yes will
cause the server to send NS records along with the SOA record for negative
answers. The default is no.



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 to yes
(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 host foo.example.com,
and the record found is "MX 10 mail.example.net", normally the address
records (A and AAAA) for mail.example.net will 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 is no.


dnssec-enable


Enable DNSSEC support in named. Unless set to yes
named behaves as if it does not support DNSSEC.
The default is no.


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).








Forwarding


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 of first,
the default, causes the server to query the forwarders first, and
if that doesn't answer the question the server will then look for
the answer itself. If only is specified, the
server will only query the forwarders.



forwarders

Specifies the IP addresses to be used
for forwarding. The default is the empty list (no forwarding).



Forwarding can also be configured on a per-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


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 Control


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, specify
allow-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 is none.






Interfaces


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.






Query 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.






Zone Transfers


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 is 10.
Increasing transfers-in may speed up the convergence
of slave zones, but it also may increase the load on the local system.



transfers-out

The maximum number of outbound zone transfers
that can be running concurrently. Zone transfer requests in excess
of the limit will be refused. The default value is 10.


transfers-per-ns

The maximum number of inbound zone transfers
that can be concurrently transferring from a given remote name server.
The default value is 2. Increasing transfers-per-ns may
speed up the convergence of slave zones, but it also may increase
the load on the remote 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.






Bad UDP Port Lists



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.





Operating System Resource Limits


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
is default.


datasize


The maximum amount of data memory the server
may use. The default is default.
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 is unlimited.


stacksize


The maximum amount of stack memory the server
may use. The default is default.






Server Resource Limits


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 is
unlimited.


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 is

1000. 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 is 100.


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 is unlimited, 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.






Periodic Task Intervals



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.









Topology


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 sortlist Statement


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; };
};




RRset Ordering


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:


[ class class_name ][ type type_name ][ name "domain_name"]
order ordering


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
are defined in the zone file.

random

Records are returned in some random order.

cyclic

Records are returned in a round-robin
order.


For example:


rrset-order {
class IN type A name "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.






Tuning




lame-ttl

Sets the number of seconds to cache a
lame server indication. 0 disables caching. (This is
NOT recommended.)
Default is 600 (10 minutes). Maximum value is
1800 (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 is 10800 seconds (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
is 2.



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 is 30 days.
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.






Built-in server information zones


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 name version.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 name hostname.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 name ID.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


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
successful queries made to the server or zone. A successful query
is defined as query which returns a NOERROR response with at least
one answer RR.

referral

The number of queries which resulted
in referral responses.

nxrrset

The number of queries which resulted in
NOERROR responses with no data.

nxdomain

The number
of queries which resulted in NXDOMAIN responses.

failure

The number of queries which resulted in a
failure response other than those above.

recursion

The number of queries which caused the server
to perform recursion in order to find the final answer.



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.






server Statement Grammar



server ip_addr {
[ bogus yes_or_no ; ]
[ provide-ixfr yes_or_no ; ]
[ request-ixfr yes_or_no ; ]
[ edns yes_or_no ; ]
[ transfers number ; ]
[ transfer-format ( one-answer | many-answers ) ; ]]
[ keys { string ; [ string ; [...]] } ; ]
[ transfer-source (ip4_addr | *) [port ip_port] ; ]
[ transfer-source-v6 (ip6_addr | *) [port ip_port] ; ]
};





server Statement Definition and Usage


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 Statement Grammar



trusted-keys {
string number number number string ;
[ string number number number string ; [...]]
};





trusted-keys Statement Definition
and Usage


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.






view Statement Grammar


view view_name
[class] {
match-clients { address_match_list } ;
match-destinations { address_match_list } ;
match-recursive-only yes_or_no ;
[ view_option; ...]
[ zone_statement; ...]
};





view Statement Definition and Usage


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 the

address_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";
};
};




zone
Statement Grammar


zone zone_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 [port ip_port] ; [ ip_addr [port ip_port] ; ... ] }; ]
[ check-names (warn|fail|ignore) ; ]
[ dialup dialup_option ; ]
[ delegation-only yes_or_no ; ]
[ file string ; ]
[ forward (only|first) ; ]
[ forwarders { [ ip_addr [port ip_port] ; ... ] }; ]
[ ixfr-base string ; ]
[ ixfr-tmp-file string ; ]
[ maintain-ixfr-base yes_or_no ; ]
[ masters [port ip_port] { ( masters_list | ip_addr [port ip_port] [key key] ) ; [...] } ; ]
[ max-ixfr-log-size number ; ]
[ max-transfer-idle-in number ; ]
[ max-transfer-idle-out number ; ]
[ max-transfer-time-in number ; ]
[ max-transfer-time-out number ; ]
[ notify yes_or_no | explicit ; ]
[ pubkey number number number string ; ]
[ 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] ; ]
[ zone-statistics yes_or_no ; ]
[ sig-validity-interval number ; ]
[ database string ; ]
[ min-refresh-time number ; ]
[ max-refresh-time number ; ]
[ min-retry-time number ; ]
[ max-retry-time number ; ]
[ multi-master yes_or_no ; ]
[ key-directory path_name; ]

}
];





zone Statement Definition and Usage




Zone Types


































master

The server has a master copy of the data
for the zone and will be able to provide authoritative answers for
it.

slave

A slave zone is a replica of a master
zone. The masters list specifies one or more IP addresses
of master servers that the slave contacts to update its copy of the zone.
Masters list elements can also be names of other masters lists.
By default, transfers are made from port 53 on the servers; this can
be changed for all servers by specifying a port number before the
list of IP addresses, or on a per-server basis after the IP address.
Authentication to the master can also be done with per-server TSIG keys.
If a file is specified, then the
replica will be written to this file whenever the zone is changed,
and reloaded from this file on a server restart. Use of a file is
recommended, since it often speeds server start-up and eliminates
a needless waste of bandwidth. Note that for large numbers (in the
tens or hundreds of thousands) of zones per server, it is best to
use a two level naming scheme for zone file names. For example,
a slave server for the zone example.com might place
the zone contents into a file called

ex/example.com where ex/ is
just the first two letters of the zone name. (Most operating systems
behave very slowly if you put 100 000 files into
a single directory.)

stub


A stub zone is similar to a slave zone,
except that it replicates only the NS records of a master zone instead
of the entire zone. Stub zones are not a standard part of the DNS;
they are a feature specific to the BIND implementation.



Stub zones can be used to eliminate the need for glue NS record
in a parent zone at the expense of maintaining a stub zone entry and
a set of name server addresses in named.conf.
This usage is not recommended for new configurations, and BIND 9
supports it only in a limited way.
In BIND 4/8, zone transfers of a parent zone
included the NS records from stub children of that zone. This meant
that, in some cases, users could get away with configuring child stubs
only in the master server for the parent zone. BIND
9 never mixes together zone data from different zones in this
way. Therefore, if a BIND 9 master serving a parent
zone has child stub zones configured, all the slave servers for the
parent zone also need to have the same child stub zones
configured.



Stub zones can also be used as a way of forcing the resolution
of a given domain to use a particular set of authoritative servers.
For example, the caching name servers on a private network using
RFC 1918 addressing may be configured with stub zones for

10.in-addr.arpa
to use a set of internal name servers as the authoritative
servers for that domain.


forward


A "forward zone" is a way to configure
forwarding on a per-domain basis. A zone statement
of type forward can contain a forward and/or forwarders statement,
which will apply to queries within the domain given by the zone
name. If no forwarders statement is present or
an empty list for forwarders is given, then no
forwarding will be done for the domain, canceling the effects of
any forwarders in the options statement. Thus
if you want to use this type of zone to change the behavior of the
global forward option (that is, "forward first
to", then "forward only", or vice versa, but want to use the same
servers as set globally) you need to re-specify the global forwarders.



hint

The initial set of root name servers is
specified using a "hint zone". When the server starts up, it uses
the root hints to find a root name server and get the most recent
list of root name servers. If no hint zone is specified for class
IN, the server uses a compiled-in default set of root servers hints.
Classes other than IN have no built-in defaults hints.

delegation-only


This is used to enforce the delegation only
status of infrastructure zones (e.g. COM, NET, ORG). Any answer that
is received without a explicit or implicit delegation in the authority
section will be treated as NXDOMAIN. This does not apply to the zone
apex. This SHOULD NOT be applied to leaf zones.


delegation-only has no effect on answers received
from forwarders.







Class


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 keyword

HS 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.





Zone Options



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 a
DNS NOTIFY message
for this zone is made up of all the listed name servers (other than
the primary master) for the zone plus any IP addresses specified
with 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
to yes then 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”.






Dynamic Update Policies


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 ) identity nametype name [ 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.




























name

Exact-match semantics. This rule matches when the
name being updated is identical to the contents of the
name field.

subdomain

This rule matches when the name being updated
is a subdomain of, or identical to, the contents of the
name field.

wildcard

The name field is
subject to DNS wildcard expansion, and this rule matches when the name
being updated name is a valid expansion of the wildcard.

self

This rule matches when the name being updated
matches the contents of the identity field.
The name field is ignored, but should be
the same as the identity field. The
self nametype is most useful when allowing using
one key per name to update, where the key has the same name as the name
to be updated. The identity would be
specified as * in this case.


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.







Zone File





Types of Resource Records and When to Use Them


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.




Resource Records


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
the type of the resource record.

TTL

the time to live of the RR. This field
is a 32 bit integer in units of seconds, and is primarily used by
resolvers when they cache RRs. The TTL describes how long a RR can
be cached before it should be discarded.

class

an encoded 16 bit value that identifies
a protocol family or instance of a protocol.

RDATA

the resource data. The format of the
data is type (and sometimes class) specific.


The following are types of valid RRs:











































































































































A

a host address. In the IN class, this is a
32-bit IP address. Described in RFC 1035.

AAAA

IPv6 address. Described in RFC 1886.

A6

IPv6 address. This can be a partial
address (a suffix) and an indirection to the name where the rest of the
address (the prefix) can be found. Experimental. Described in RFC 2874.

AFSDB

location of AFS database servers.
Experimental. Described in RFC 1183.

APL

address prefix list. Experimental.
Described in RFC 3123.

CERT

holds a digital certificate.
Described in RFC 2538.

CNAME

identifies the canonical name of an alias.
Described in RFC 1035.

DNAME

Replaces the domain name specified with
another name to be looked up, effectively aliasing an entire
subtree of the domain name space rather than a single record
as in the case of the CNAME RR.
Described in RFC 2672.

GPOS

Specifies the global position. Superseded by LOC.

HINFO

identifies the CPU and OS used by a host.
Described in RFC 1035.

ISDN

representation of ISDN addresses.
Experimental. Described in RFC 1183.

KEY

stores a public key associated with a
DNS name. Described in RFC 2535.

KX

identifies a key exchanger for this
DNS name. Described in RFC 2230.

LOC

for storing GPS info. Described in RFC 1876.
Experimental.

MX

identifies a mail exchange for the domain.
a 16 bit preference value (lower is better)
followed by the host name of the mail exchange.
Described in RFC 974, RFC 1035.

NAPTR

name authority pointer. Described in RFC 2915.

NSAP

a network service access point.
Described in RFC 1706.

NS

the authoritative name server for the
domain. Described in RFC 1035.

NXT

used in DNSSEC to securely indicate that
RRs with an owner name in a certain name interval do not exist in
a zone and indicate what RR types are present for an existing name.
Described in RFC 2535.

PTR

a pointer to another part of the domain
name space. Described in RFC 1035.

PX

provides mappings between RFC 822 and X.400
addresses. Described in RFC 2163.

RP

information on persons responsible
for the domain. Experimental. Described in RFC 1183.

RT

route-through binding for hosts that
do not have their own direct wide area network addresses.
Experimental. Described in RFC 1183.

SIG

("signature") contains data authenticated
in the secure DNS. Described in RFC 2535.

SOA

identifies the start of a zone of authority.
Described in RFC 1035.

SRV

information about well known network
services (replaces WKS). Described in RFC 2782.

TXT

text records. Described in RFC 1035.

WKS

information about which well known
network services, such as SMTP, that a domain supports. Historical.

X25

representation of X.25 network addresses.
Experimental. Described in RFC 1183.


The following classes of resource records
are currently valid in the DNS:






















IN

The Internet.

CH


CHAOSnet, a LAN protocol created at MIT in the mid-1970s.
Rarely used for its historical purpose, but reused for BIND's
built-in server information zones, e.g.,
version.bind.

HS


Hesiod, an information service
developed by MIT's Project Athena. It is used to share information
about various systems databases, such as users, groups, printers
and so on.


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.





Textual expression of RRs


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:











































ISI.EDU.

MX

10 VENERA.ISI.EDU.


MX

10 VAXA.ISI.EDU

VENERA.ISI.EDU

A

128.9.0.32


A

10.1.0.52

VAXA.ISI.EDU

A

10.2.0.27


A

128.9.0.33


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:






















XX.LCS.MIT.EDU. IN

A

10.0.0.44

CH

A

MIT.EDU. 2420


This example shows two addresses for XX.LCS.MIT.EDU,
each of a different class.






Discussion of MX Records



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.



















































example.com.

IN

MX

10

mail.example.com.


IN

MX

10

mail2.example.com.


IN

MX

20

mail.backup.org.

mail.example.com.

IN

A

10.0.0.1


mail2.example.com.

IN

A

10.0.0.2



For example:


Mail delivery will be attempted to mail.example.com and

mail2.example.com (in
any order), and if neither of those succeed, delivery to mail.backup.org will
be attempted.





Setting TTLs


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
caching TTL. This controls how long other servers will cache no-such-domain
(NXDOMAIN) responses from you.


The maximum time for
negative caching is 3 hours (3h).


$TTL

The $TTL directive at the top of the
zone file (before the SOA) gives a default TTL for every RR without
a specific TTL set.

RR TTLs

Each RR can have a TTL as the second
field in the RR, which will control how long other servers can cache
the it.


All of these TTLs default to units of seconds, though units
can be explicitly specified, for example, 1h30m.





Inverse Mapping in IPv4



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:


















$ORIGIN

2.1.10.in-addr.arpa

3

IN PTR foo.example.com.



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.







Other Zone File Directives


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.





The $ORIGIN Directive


Syntax: $ORIGIN
domain-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.




The $INCLUDE Directive


Syntax: $INCLUDE

filename [
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.







The $TTL Directive


Syntax: $TTL
default-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.






BIND Master File Extension: the $GENERATE Directive



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
or start-stop/step. If the first form is used then step is set to
1. All of start, stop and step must be positive.

lhs


lhs describes the
owner name of the resource records to be created. Any single $ symbols
within the lhs side are replaced by the iterator
value.
To get a $ in the output you need to escape the $

using a backslash \,
e.g. \$. The $ may optionally be followed
by modifiers which change the offset from the iterator, field width and base.
Modifiers are introduced by a { immediately following the
$ as ${offset[,width[,base]]}.
e.g. ${-20,3,d} which subtracts 20 from the current value,
prints the result as a decimal in a zero padded field of with 3. Available
output forms are decimal (d), octal (o)
and hexadecimal (x or X for uppercase).
The default modifier is ${0,0,d}.
If the lhs is not
absolute, the current $ORIGIN is appended to
the name.



For compatibility with earlier versions $$ is still
recognized a indicating a literal $ in the output.


ttl


ttl specifies the
ttl of the generated records. If not specified this will be
inherited using the normal ttl inheritance rules.


class and ttl can be
entered in either order.



class


class specifies the
class of the generated records. This must match the zone class if
it is specified.


class and ttl can be
entered in either order.



type

At present the only supported types are
PTR, CNAME, DNAME, A, AAAA and NS.

rhs

rhs is a domain name. It is processed
similarly to lhs.


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.