Table of Contents
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.
Following is a list of elements used throughout the BIND configuration file documentation:
|
|
The name of an |
|
|
A list of one or more
|
|
|
A named list of one or more |
|
|
A quoted string which will be used as
a DNS name, for example " |
|
|
One to four integers valued 0 through 255 separated by dots (`.'), such as 123, 45.67 or 89.123.45.67. |
|
|
An IPv4 address with exactly four elements
in |
|
|
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. |
|
|
An |
|
|
An IP port |
|
|
An IP network specified as an |
|
|
A |
|
|
A list of one or more
|
|
|
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. |
|
|
A quoted string which will be used as
a pathname, such as |
|
|
A list of an |
|
|
A number, the word
An
A
The value must be representable as a 64-bit unsigned integer
(0 to 18446744073709551615, inclusive).
Using |
|
|
Either |
|
|
One of |
address_match_list= address_match_list_element ; [ address_match_list_element; ... ]address_match_list_element= [ ! ] (ip_address [/length] | key key_id | acl_name | { address_match_list } )
Address match lists are primarily used to determine access control for various server operations. They are also used in the listen-on and sortlist statements. The elements which constitute an address match list can be any of the following:
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-query-cache, allow-transfer, allow-update, allow-update-forwarding, and blackhole all use address match lists. Similarly, the listen-on option will cause the server to not accept queries on any of the machine's addresses which do not match the list.
Because of the first-match aspect of the algorithm, an element that defines a subset of another element in the list should come before the broader element, regardless of whether either is negated. For example, in 1.2.3/24; ! 1.2.3.13; the 1.2.3.13 element is completely useless because the algorithm will match any lookup for 1.2.3.13 to the 1.2.3/24 element. Using ! 1.2.3.13; 1.2.3/24 fixes that problem by having 1.2.3.13 blocked by the negation but all other 1.2.3.* hosts fall through.
The BIND 9 comment syntax allows for comments to appear anywhere that whitespace may appear in a BIND configuration file. To appeal to programmers of all kinds, they can be written in the C, C++, or shell/perl style.
/* This is a BIND comment as in C */
// This is a BIND comment as in C++
# This is a BIND comment as in common UNIX shells and perl
Comments may appear anywhere that whitespace may appear in a BIND configuration file.
C-style comments start with the two characters /* (slash, star) and end with */ (star, slash). Because they are completely delimited with these characters, they can be used to comment only a portion of a line or to span multiple lines.
C-style comments cannot be nested. For example, the following is not valid because the entire comment ends with the first */:
/* This is the start of a comment. This is still part of the comment. /* This is an incorrect attempt at nesting a comment. */ This is no longer in any comment. */
C++-style comments start with the two characters // (slash, slash) and continue to the end of the physical line. They cannot be continued across multiple physical lines; to have one logical comment span multiple lines, each line must use the // pair. For example:
// This is the start of a comment. The next line // is a new comment, even though it is logically // part of the previous comment.
Shell-style (or perl-style, if you prefer) comments start
with the character # (number sign)
and continue to the end of the
physical line, as in C++ comments.
For example:
# This is the start of a comment. The next line # is a new comment, even though it is logically # part of the previous comment.
You cannot use the semicolon (`;') character to start a comment such as you would in a zone file. The semicolon indicates the end of a configuration statement.
A BIND 9 configuration consists of statements and comments. Statements end with a semicolon. Statements and comments are the only elements that can appear without enclosing braces. Many statements contain a block of sub-statements, which are also terminated with a semicolon.
The following statements are supported:
|
acl |
defines a named IP address 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.
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 { [ inet ( ip_addr | * ) [ port ip_port ] allow {address_match_list} keys {key_list}; ] [ inet ...; ] [ unixpathpermnumberownernumbergroupnumberkeys {key_list}; ] [ unix ...; ] };
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 * (asterisk) 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. The asterisk
"*" 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.
A unix control channel is a UNIX domain socket listening at the specified path in the file system. Access to the socket is specified by the perm, owner and group clauses. Note on some platforms (SunOS and Solaris) the permissions (perm) are applied to the parent directory as the permissions on the socket itself 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
a
rndc.conf file and make it group
readable by a group
that contains the users who should have access.
To disable the command channel, use an empty controls statement: controls { };.
The include statement inserts the specified file at the point where the include statement is encountered. The include statement facilitates the administration of configuration files by permitting the reading or writing of some things but not others. For example, the statement could include private keys that are readable only by the name server.
The key statement defines a shared secret key for use with TSIG (see the section called “TSIG”) or the command channel (see the section called “controls Statement Definition and Usage”).
The key statement can occur at the top level of the configuration file or inside a view statement. Keys defined in top-level key statements can be used in all views. Keys intended for use in a controls statement (see the section called “controls Statement Definition and Usage”) must be defined at the top level.
The key_id, also known as the
key name, is a domain name uniquely identifying the key. It can
be used in a server
statement to cause requests sent to that
server to be signed with this key, or in address match lists to
verify that incoming requests have been signed with a key
matching this name, algorithm, and secret.
The algorithm_id is a string
that specifies a security/authentication algorithm. Named
supports hmac-md5,
hmac-sha1, hmac-sha224,
hmac-sha256, hmac-sha384
and hmac-sha512 TSIG authentication.
Truncated hashes are supported by appending the minimum
number of required bits preceded by a dash, e.g.
hmac-sha1-80. The
secret_string is the secret
to be used by the algorithm, and is treated as a base-64
encoded string.
logging { [ channelchannel_name{ ( filepath_name[ versions (number| unlimited ) ] [ sizesize spec] | syslogsyslog_facility| stderr | null ); [ severity (critical|error|warning|notice|info|debug[level] |dynamic); ] [ print-categoryyesorno; ] [ print-severityyesorno; ] [ print-timeyesorno; ] }; ] [ categorycategory_name{channel_name; [channel_name; ... ] }; ] ... };
The logging statement configures a wide variety of logging options for the name server. Its channel phrase associates output methods, format options and severity levels with a name that can then be used with the category phrase to select how various classes of messages are logged.
Only one logging statement is used to define as many channels and categories as are wanted. If there is no logging statement, the logging configuration will be:
logging {
category default { default_syslog; default_debug; };
category unmatched { null; };
};
In BIND 9, the logging configuration
is only established when
the entire configuration file has been parsed. In BIND 8, it was
established as soon as the logging
statement
was parsed. When the server is starting up, all logging messages
regarding syntax errors in the configuration file go to the default
channels, or to standard error if the "-g" option
was specified.
All log output goes to one or more channels; you can make as many of them as you want.
Every channel definition must include a destination clause that says whether messages selected for the channel go to a file, to a particular syslog facility, to the standard error stream, or are discarded. It can optionally also limit the message severity level that will be accepted by the channel (the default is info), and whether to include a named-generated time stamp, the category name and/or severity level (the default is not to include any).
The null destination clause causes all messages sent to the channel to be discarded; in that case, other options for the channel are meaningless.
The file destination clause directs the channel to a disk file. It can include limitations both on how large the file is allowed to become, and how many versions of the file will be saved each time the file is opened.
If you use the versions log file
option, then
named will retain that many backup
versions of the file by
renaming them when opening. For example, if you choose to keep
three 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 rndc
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 logs 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 called named.run
in the server's working directory.
For security reasons, when the "-u"
command line option is used, the named.run file
is created only after named has
changed to the
new UID, and any debug output generated while named is
starting up and still running as root is discarded. If you need
to capture this output, you must run the server with the "-g"
option and redirect standard error to a file.
Once a channel is defined, it cannot be redefined. Thus you cannot alter the built-in channels directly, but you can modify the default logging by pointing categories at channels you have defined.
There are many categories, so you can send the logs you want to see wherever you want, without seeing logs you don't want. If you don't specify a list of channels for a category, then log messages in that category will be sent to the default category instead. If you don't specify a default category, the following "default default" is used:
category default { default_syslog; default_debug; };
As an example, let's say you want to log security events to a file, but you also want keep the default logging behavior. You'd specify the following:
channel my_security_channel {
file "my_security_file";
severity info;
};
category security {
my_security_channel;
default_syslog;
default_debug;
};
To discard all messages in a category, specify the null channel:
category xfer-out { null; };
category notify { null; };
Following are the available categories and brief descriptions of the types of log information they contain. More categories may be added in future BIND releases.
|
default |
The default category defines the logging 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, specifying 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, and 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).
|
|
query-errors |
Information about queries that resulted in some failure. |
|
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 been forced to NXDOMAIN as the result of a delegation-only zone or a delegation-only in a hint or stub zone declaration. |
The query-errors category is specifically intended for debugging purposes: To identify why and how specific queries result in responses which indicate an error. Messages of this category are therefore only logged with debug levels.
At the debug levels of 1 or higher, each response with the rcode of SERVFAIL is logged as follows:
client 127.0.0.1#61502: query failed (SERVFAIL) for www.example.com/IN/AAAA at query.c:3880
This means an error resulting in SERVFAIL was
detected at line 3880 of source file
query.c.
Log messages of this level will particularly
help identify the cause of SERVFAIL for an
authoritative server.
At the debug levels of 2 or higher, detailed context information of recursive resolutions that resulted in SERVFAIL is logged. The log message will look like as follows:
fetch completed at resolver.c:2970 for www.example.com/A
in 30.000183: timed out/success [domain:example.com,
referral:2,restart:7,qrysent:8,timeout:5,lame:0,neterr:0,
badresp:1,adberr:0,findfail:0,valfail:0]
The first part before the colon shows that a recursive
resolution for AAAA records of www.example.com completed
in 30.000183 seconds and the final result that led to the
SERVFAIL was determined at line 2970 of source file
resolver.c.
The following part shows the detected final result and the latest result of DNSSEC validation. The latter is always success when no validation attempt is made. In this example, this query resulted in SERVFAIL probably because all name servers are down or unreachable, leading to a timeout in 30 seconds. DNSSEC validation was probably not attempted.
The last part enclosed in square brackets shows statistics
information collected for this particular resolution
attempt.
The domain field shows the deepest zone
that the resolver reached;
it is the zone where the error was finally detected.
The meaning of the other fields is summarized in the
following table.
|
|
The number of referrals the resolver received throughout the resolution process. In the above example this is 2, which are most likely com and example.com. |
|
|
The number of cycles that the resolver tried
remote servers at the |
|
|
The number of queries the resolver sent at the
|
|
|
The number of timeouts since the resolver received the last response. |
|
|
The number of lame servers the resolver detected
at the |
|
|
The number of erroneous results that the
resolver encountered in sending queries
at the |
|
|
The number of unexpected responses (other than
|
|
|
Failures in finding remote server addresses
of the |
|
|
Failures of resolving remote server addresses. This is a total number of failures throughout the resolution process. |
|
|
Failures of DNSSEC validation.
Validation failures are counted throughout
the resolution process (not limited to
the |
At the debug levels of 3 or higher, the same messages as those at the debug 1 level are logged for other errors than SERVFAIL. Note that negative responses such as NXDOMAIN are not regarded as errors here.
At the debug levels of 4 or higher, the same messages as those at the debug 2 level are logged for other errors than SERVFAIL. Unlike the above case of level 3, messages are logged for negative responses. This is because any unexpected results can be difficult to debug in the recursion case.
This is the grammar of the lwres
statement in the named.conf file:
lwres { [ listen-on {ip_addr[portip_port] ; [ip_addr[portip_port] ; ... ] }; ] [ viewview_name; ] [ search {domain_name; [domain_name; ... ] }; ] [ ndotsnumber; ] };
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 multiple lwres statements configuring lightweight resolver servers with different properties.
The listen-on statement specifies a list of addresses (and ports) that this instance of a lightweight resolver daemon should accept requests on. If no port is specified, port 921 is used. If this statement is omitted, requests will be accepted on 127.0.0.1, port 921.
The view statement binds this instance of a lightweight resolver daemon to a view in the DNS namespace, so that the response will be constructed in the same manner as a normal DNS query matching this view. If this statement is omitted, the default view is used, and if there is no default view, an error is triggered.
The search statement is equivalent to
the
search statement in
/etc/resolv.conf. It provides a
list of domains
which are appended to relative names in queries.
The ndots statement is equivalent to
the
ndots statement in
/etc/resolv.conf. It indicates the
minimum
number of dots in a relative domain name that should result in an
exact match lookup before search path elements are appended.
mastersname[portip_port] { (masters_list|ip_addr[portip_port] [keykey] ) ; [...] };
masters lists allow for a common set of masters to be easily used by multiple stub and slave zones.
This is the grammar of the options
statement in the named.conf file:
options { [ versionversion_string; ] [ hostnamehostname_string; ] [ server-idserver_id_string; ] [ directorypath_name; ] [ key-directorypath_name; ] [ named-xferpath_name; ] [ tkey-domaindomainname; ] [ tkey-dhkeykey_namekey_tag; ] [ cache-filepath_name; ] [ dump-filepath_name; ] [ memstatistics-filepath_name; ] [ pid-filepath_name; ] [ recursing-filepath_name; ] [ statistics-filepath_name; ] [ zone-statisticsyes_or_no; ] [ auth-nxdomainyes_or_no; ] [ deallocate-on-exityes_or_no; ] [ dialupdialup_option; ] [ fake-iqueryyes_or_no; ] [ fetch-glueyes_or_no; ] [ flush-zones-on-shutdownyes_or_no; ] [ has-old-clientsyes_or_no; ] [ host-statisticsyes_or_no; ] [ host-statistics-maxnumber; ] [ minimal-responsesyes_or_no; ] [ multiple-cnamesyes_or_no; ] [ notifyyes_or_no|explicit|master-only; ] [ recursionyes_or_no; ] [ rfc2308-type1yes_or_no; ] [ use-id-poolyes_or_no; ] [ maintain-ixfr-baseyes_or_no; ] [ ixfr-from-differences (yes_or_no|master|slave); ] [ dnssec-enableyes_or_no; ] [ dnssec-validationyes_or_no; ] [ dnssec-lookasidedomaintrust-anchordomain; ] [ dnssec-must-be-securedomain yes_or_no; ] [ dnssec-accept-expiredyes_or_no; ] [ forward (only|first); ] [ forwarders { [ip_addr[portip_port] ; ... ] }; ] [ dual-stack-servers [portip_port] { (domain_name[portip_port] |ip_addr[portip_port] ) ; ... }; ] [ check-names (master|slave|response) (warn|fail|ignore); ] [ check-mx (warn|fail|ignore); ] [ check-wildcardyes_or_no; ] [ check-integrityyes_or_no; ] [ check-mx-cname (warn|fail|ignore); ] [ check-srv-cname (warn|fail|ignore); ] [ check-siblingyes_or_no; ] [ allow-notify {address_match_list}; ] [ allow-query {address_match_list}; ] [ allow-query-cache {address_match_list}; ] [ allow-transfer {address_match_list}; ] [ allow-recursion {address_match_list}; ] [ allow-update {address_match_list}; ] [ allow-update-forwarding {address_match_list}; ] [ update-check-kskyes_or_no; ] [ allow-v6-synthesis {address_match_list}; ] [ blackhole {address_match_list}; ] [ use-v4-udp-ports {port_list}; ] [ avoid-v4-udp-ports {port_list}; ] [ use-v6-udp-ports {port_list}; ] [ avoid-v6-udp-ports {port_list}; ] [ listen-on [ portip_port] {address_match_list}; ] [ listen-on-v6 [ portip_port] {address_match_list}; ] [ query-source ( (ip4_addr|*) [ port (ip_port|*) ] | [ address (ip4_addr|*) ] [ port (ip_port|*) ] ) ; ] [ query-source-v6 ( (ip6_addr|*) [ port (ip_port|*) ] | [ address (ip6_addr|*) ] [ port (ip_port|*) ] ) ; ] [ max-transfer-time-innumber; ] [ max-transfer-time-outnumber; ] [ max-transfer-idle-innumber; ] [ max-transfer-idle-outnumber; ] [ tcp-clientsnumber; ] [ reserved-socketsnumber; ] [ recursive-clientsnumber; ] [ serial-query-ratenumber; ] [ serial-queriesnumber; ] [ tcp-listen-queuenumber; ] [ transfer-format( one-answer | many-answers ); ] [ transfers-innumber; ] [ transfers-outnumber; ] [ transfers-per-nsnumber; ] [ transfer-source (ip4_addr|*) [portip_port] ; ] [ transfer-source-v6 (ip6_addr|*) [portip_port] ; ] [ alt-transfer-source (ip4_addr|*) [portip_port] ; ] [ alt-transfer-source-v6 (ip6_addr|*) [portip_port] ; ] [ use-alt-transfer-sourceyes_or_no; ] [ notify-delayseconds; ] [ notify-source (ip4_addr|*) [portip_port] ; ] [ notify-source-v6 (ip6_addr|*) [portip_port] ; ] [ also-notify {ip_addr[portip_port] ; [ip_addr[portip_port] ; ... ] }; ] [ max-ixfr-log-sizenumber; ] [ max-journal-sizesize_spec; ] [ coresizesize_spec; ] [ datasizesize_spec; ] [ filessize_spec; ] [ stacksizesize_spec; ] [ cleaning-intervalnumber; ] [ heartbeat-intervalnumber; ] [ interface-intervalnumber; ] [ statistics-intervalnumber; ] [ topology {address_match_list}]; [ sortlist {address_match_list}]; [ rrset-order {order_spec; [order_spec; ... ] ] }; [ lame-ttlnumber; ] [ max-ncache-ttlnumber; ] [ max-cache-ttlnumber; ] [ sig-validity-intervalnumber; ] [ min-rootsnumber; ] [ use-ixfryes_or_no; ] [ provide-ixfryes_or_no; ] [ request-ixfryes_or_no; ] [ treat-cr-as-spaceyes_or_no; ] [ min-refresh-timenumber; ] [ max-refresh-timenumber; ] [ min-retry-timenumber; ] [ max-retry-timenumber; ] [ portip_port; ] [ additional-from-authyes_or_no; ] [ additional-from-cacheyes_or_no; ] [ random-devicepath_name; ] [ max-cache-sizesize_spec; ] [ match-mapped-addressesyes_or_no; ] [ preferred-glue (A|AAAA|NONE); ] [ edns-udp-sizenumber; ] [ max-udp-sizenumber; ] [ root-delegation-only [ exclude {namelist} ] ; ] [ querylogyes_or_no; ] [ disable-algorithmsdomain{algorithm; [algorithm; ] }; ] [ acache-enableyes_or_no; ] [ acache-cleaning-intervalnumber; ] [ max-acache-sizesize_spec; ] [ clients-per-querynumber; ] [ max-clients-per-querynumber; ] [ masterfile-format (text|raw) ; ] [ empty-servername; ] [ empty-contactname; ] [ empty-zones-enableyes_or_no; ] [ disable-empty-zonezone_name; ] [ zero-no-soa-ttlyes_or_no; ] [ zero-no-soa-ttl-cacheyes_or_no; ] };
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.
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.
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.
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.
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.
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.
This is for testing only. Do not use.
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.
The pathname of the file the server writes memory usage statistics to on exit. If specified the statistics will be written to the file on exit.
In BIND 9.5 and later this will
default to named.memstats.
BIND 9.5 will also introduce
memstatistics to control the
writing.
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 filename, and therefore is not enclosed
in
double quotes.
The pathname of the file the server dumps
the queries that are currently recursing when instructed
to do so with rndc recursing.
If not specified, the default is named.recursing.
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”.
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.
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.
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 prefer any type (NONE).
Turn on enforcement of delegation-only in TLDs (top level domains) and root zones with an optional exclude list.
DS queries are expected to be made to and be answered by delegation only zones. Such queries and responses are treated as a exception to delegation-only processing and are not converted to NXDOMAIN responses provided a CNAME is not discovered at the query name.
If a delegation only zone server also serves a child zone it is not always possible to determine whether a answer comes from the delegation only zone or the child zone. SOA NS and DNSKEY records are apex only records and a matching response that contains these records or DS is treated as coming from a child zone. RRSIG records are also examined to see if they are signed by a child zone or not. The authority section is also examined to see if there is evidence that the answer is from the child zone. Answers that are determined to be from a child zone are not converted to NXDOMAIN responses. Despite all these checks there is still a possibility of false negatives when a child zone is being served.
Similarly false positives can arise from empty nodes (no records at the name) in the delegation only zone when the query type is not ANY.
Note some TLDs are not delegation only (e.g. "DE", "LV", "US" and "MUSEUM"). This list is not exhaustive.
options {
root-delegation-only exclude { "de"; "lv"; "us"; "museum"; };
};
Disable the specified DNSSEC algorithms at and below the specified name. Multiple disable-algorithms statements are allowed. Only the most specific will be applied.
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.
Specify hierarchies which must be or 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.
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.
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.
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.
In BIND 8, this option enabled simulating the obsolete DNS query type IQUERY. BIND 9 never does IQUERY simulation.
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.
When the nameserver exits due receiving SIGTERM,
flush or do not flush any pending zone writes. The default
is
flush-zones-on-shutdown no.
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.
In BIND 8, this enables keeping of statistics for every host that the name server interacts with. Not implemented in BIND 9.
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.
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.
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 onwards always strictly enforces the CNAME rules both in master files and dynamic updates.
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 master-only, notifies are only
sent
for master zones.
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.
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.
Setting this to yes will
cause the server to send NS records along with the SOA
record for negative
answers. The default is no.
Not yet implemented in BIND 9.
This option is obsolete. BIND 9 always allocates query IDs from a pool.
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”.
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)”.
See the description of provide-ixfr in the section called “server Statement Definition and Usage”.
See the description of request-ixfr in the section called “server Statement Definition and Usage”.
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.
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.
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.
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.
ixfr-from-differences also accepts master and slave at the view and options levels which causes ixfr-from-differences to be enabled for all master or slave zones respectively. It is off by default.
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.
Enable DNSSEC support in named. Unless set to yes,
named behaves as if it does not support DNSSEC.
The default is yes.
Enable DNSSEC validation in named.
Note dnssec-enable also needs to be
set to yes to be effective.
The default is no.
Accept expired signatures when verifying DNSSEC signatures.
The default is no.
Setting this option to "yes" leaves named vulnerable to replay attacks.
Specify whether query logging should be started when named starts. If querylog is not specified, then the query logging is determined by the presence of the logging category queries.
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 answers received from the network (response) the default is ignore.
The rules for legal hostnames and mail domains are derived from RFC 952 and RFC 821 as modified by RFC 1123.
check-names applies to the owner names of A, AAAA and MX records. It also applies to the domain names in the RDATA of NS, SOA, MX, and SRV 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, or IP6.INT).
Check whether the MX record appears to refer to a IP address. The default is to warn. Other possible values are fail and ignore.
This option is used to check for non-terminal wildcards. The use of non-terminal wildcards is almost always as a result of a failure to understand the wildcard matching algorithm (RFC 1034). This option affects master zones. The default (yes) is to check for non-terminal wildcards and issue a warning.
Perform post load zone integrity checks on master zones. This checks that MX and SRV records refer to address (A or AAAA) records and that glue address records exist for delegated zones. For MX and SRV records only in-zone hostnames are checked (for out-of-zone hostnames use named-checkzone). For NS records only names below top of zone are checked (for out-of-zone names and glue consistency checks use named-checkzone). The default is yes.
If check-integrity is set then fail, warn or ignore MX records that refer to CNAMES. The default is to warn.
If check-integrity is set then fail, warn or ignore SRV records that refer to CNAMES. The default is to warn.
When performing integrity checks, also check that sibling glue exists. The default is yes.
When returning authoritative negative responses to SOA queries set the TTL of the SOA record returned in the authority section to zero. The default is yes.
When caching a negative response to a SOA query set the TTL to zero. The default is no.
When regenerating the RRSIGs following a UPDATE request to a secure zone, check the KSK flag on the DNSKEY RR to determine if this key should be used to generate the RRSIG. This flag is ignored if there are not DNSKEY RRs both with and without a KSK. The default is yes.
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.
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.
Specifies the IP addresses to be used for forwarding. The default is the empty list (no forwarding).
Forwarding can also be configured on a per-domain basis, allowing for the global forwarding options to be overridden in a variety of ways. You can set particular domains to use different forwarders, or have a different forward only/first behavior, or not forward at all, see the section called “zone Statement Grammar”.
Dual-stack servers are used as servers of last resort to work around problems in reachability due the lack of support for either IPv4 or IPv6 on the host machine.
Specifies host names or addresses of machines with access to both IPv4 and IPv6 transports. If a hostname is used, the server must be able to resolve the name using only the transport it has. If the machine is dual stacked, then the dual-stack-servers have no effect unless access to a transport has been disabled on the command line (e.g. named -4).
Access to the server can be restricted based on the IP address of the requesting system. See the section called “Address Match Lists” for details on how to specify IP address lists.
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.
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-query-cache is now used to specify access to the cache.
Specifies which hosts are allowed to get answers from the cache. If allow-query-cache is not set then allow-recursion is used if set, otherwise allow-query is used if set unless recursion no; is set in which case none; is used, otherwise the default (localnets; localhost;) is used.
Specifies which hosts are allowed to make recursive queries through this server. If allow-recursion is not set then allow-query-cache is used if set, otherwise allow-query is used if set, otherwise the default (localnets; localhost;) is used.
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.
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.
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.
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.
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.
The interfaces and ports that the server will answer queries
from may be specified using the listen-on option. listen-on takes
an optional port and an address_match_list.
The server will listen on all interfaces allowed by the address
match list. If a port is not specified, port 53 will be used.
Multiple listen-on statements are allowed. For example,
listen-on { 5.6.7.8; };
listen-on port 1234 { !1.2.3.4; 1.2/16; };
will enable the name server on port 53 for the IP address 5.6.7.8, and on port 1234 of an address on the machine in net 1.2 that is not 1.2.3.4.
If no listen-on is specified, the server will listen on port 53 on all interfaces.
The listen-on-v6 option is used to specify the interfaces and the ports on which the server will listen for incoming queries sent using IPv6.
When
{ any; }
is
specified
as the address_match_list for the
listen-on-v6 option,
the server does not bind a separate socket to each IPv6 interface
address as it does for IPv4 if the operating system has enough API
support for IPv6 (specifically if it conforms to RFC 3493 and RFC
3542).
Instead, it listens on the IPv6 wildcard address.
If the system only has incomplete API support for IPv6, however,
the behavior is the same as that for IPv4.
A list of particular IPv6 addresses can also be specified, in which case the server listens on a separate socket for each specified address, regardless of whether the desired API is supported by the system.
Multiple listen-on-v6 options can be used. For example,
listen-on-v6 { any; };
listen-on-v6 port 1234 { !2001:db8::/32; any; };
will enable the name server on port 53 for any IPv6 addresses (with a single wildcard socket), and on port 1234 of IPv6 addresses that is not in the prefix 2001:db8::/32 (with separate sockets for each matched address.)
To make the server not listen on any IPv6 address, use
listen-on-v6 { none; };
If no listen-on-v6 option is specified, the server will not listen on any IPv6 address.
If the server doesn't know the answer to a question, it will query other name servers. query-source specifies the address and port used for such queries. For queries sent over IPv6, there is a separate query-source-v6 option. If address is * (asterisk) or is omitted, a wildcard IP address (INADDR_ANY) will be used.
If port is * or is omitted, a random port number from a pre-configured range is picked up and will be used for each query. The port range(s) is that specified in the use-v4-udp-ports (for IPv4) and use-v6-udp-ports (for IPv6) options, excluding the ranges specified in the avoid-v4-udp-ports and avoid-v6-udp-ports options, respectively.
The defaults of the query-source and query-source-v6 options are:
query-source address * port *; query-source-v6 address * port *;
If use-v4-udp-ports or use-v6-udp-ports is unspecified, named will check if the operating system provides a programming interface to retrieve the system's default range for ephemeral ports. If such an interface is available, named will use the corresponding system default range; otherwise, it will use its own defaults:
use-v4-udp-ports { range 1024 65535; };
use-v6-udp-ports { range 1024 65535; };
Note: make sure the ranges be sufficiently large for security. A desirable size depends on various parameters, but we generally recommend it contain at least 16384 ports (14 bits of entropy). Note also that the system's default range when used may be too small for this purpose, and that the range may even be changed while named is running; the new range will automatically be applied when named is reloaded. It is encouraged to configure use-v4-udp-ports and use-v6-udp-ports explicitly so that the ranges are sufficiently large and are reasonably independent from the ranges used by other applications.
Note: the operational configuration where named runs may prohibit the use of some ports. For example, UNIX systems will not allow named running without a root privilege to use ports less than 1024. If such ports are included in the specified (or detected) set of query ports, the corresponding query attempts will fail, resulting in resolution failures or delay. It is therefore important to configure the set of ports that can be safely used in the expected operational environment.
The defaults of the avoid-v4-udp-ports and avoid-v6-udp-ports options are:
avoid-v4-udp-ports {};
avoid-v6-udp-ports {};
Note: it is generally strongly discouraged to specify a particular port for the query-source or query-source-v6 options; it implicitly disables the use of randomized port numbers and can be insecure.
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.
Solaris 2.5.1 and earlier does not support setting the source address for TCP sockets.
See also transfer-source and notify-source.
BIND has mechanisms in place to facilitate zone transfers and set limits on the amount of load that transfers place on the system. The following options apply to zone transfers.
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. Optionally, a port may be specified with each also-notify address to send the notify messages to a port other than the default of 53. 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).
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).
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).
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).
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).
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.
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.
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 BIND 4.9.5 onwards. The many-answers format is also supported by recent Microsoft Windows nameservers. The default is many-answers. transfer-format may be overridden on a per-server basis by using the server statement.
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.
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.
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 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.
Solaris 2.5.1 and earlier does not support setting the source address for TCP sockets.
The same as transfer-source, except zone transfers are performed using IPv6.
An alternate transfer source if the one listed in transfer-source fails and use-alt-transfer-source is set.
An alternate transfer source if the one listed in transfer-source-v6 fails and use-alt-transfer-source is set.
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 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 or per-view basis by including a notify-source statement within the zone or view block in the configuration file.
Solaris 2.5.1 and earlier does not support setting the source address for TCP sockets.
Like notify-source, but applies to notify messages sent to IPv6 addresses.
use-v4-udp-ports, avoid-v4-udp-ports, use-v6-udp-ports, and avoid-v6-udp-ports specify a list of IPv4 and IPv6 UDP ports that will be used or not used as source ports for UDP messages. See the section called “Query Address” about how the available ports are determined. For example, with the following configuration
use-v6-udp-ports { range 32768 65535; };
avoid-v6-udp-ports { 40000; range 50000 60000; };
UDP ports of IPv6 messages sent from named will be in one of the following ranges: 32768 to 39999, 40001 to 49999, and 60001 to 65535.
avoid-v4-udp-ports and avoid-v6-udp-ports can be used to prevent named from choosing as its random source port a port that is blocked by your firewall or a port that is used by other applications; if a query went out with a source port blocked by a firewall, the answer would not get by the firewall and the name server would have to query again. Note: the desired range can also be represented only with use-v4-udp-ports and use-v6-udp-ports, and the avoid- options are redundant in that sense; they are provided for backward compatibility and to possibly simplify the port specification.
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.
The maximum size of a core dump. The default
is default.
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.
The maximum number of files the server
may have open concurrently. The default is unlimited.
The maximum amount of stack memory the server
may use. The default is default.
The following options set limits on the server's resource consumption that are enforced internally by the server rather than the operating system.
This option is obsolete; it is accepted and ignored for BIND 8 compatibility. The option max-journal-size performs a similar function in BIND 9.
Sets a maximum size for each journal file
(see 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.
This may also be set on a per-zone basis.
In BIND 8, specifies the maximum number of host statistics entries to be kept. Not implemented in BIND 9.
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.
The maximum number of simultaneous client TCP
connections that the server will accept.
The default is 100.
The number of file descriptors reserved for TCP, stdio,
etc. This needs to be big enough to cover the number of
interfaces named listens on, tcp-clients as well as
to provide room for outgoing TCP queries and incoming zone
transfers. The default is 512.
The minimum value is 128 and the
maximum value is 128 less than
maxsockets (-S). This option may be removed in the future.
This option has little effect on Windows.
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.
A value of 0 is special, meaning that
records are purged from the cache only when their
TTLs expire.
Another special keyword unlimited
means the maximum value of 32-bit unsigned integers
(0xffffffff), which may not have the same effect as
0 on machines that support more than 32 bits of
memory space.
Any positive values less than 2MB will be ignored reset
to 2MB.
In a server with multiple views, the limit applies
separately to the cache of each view.
The default is 0.
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.
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.
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.
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.
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.
Not yet implemented in BIND 9.
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; };
The topology option is not implemented in BIND 9.
The response to a DNS query may consist of multiple resource records (RRs) forming a resource records set (RRset). The name server will normally return the RRs within the RRset in an indeterminate order (but see the rrset-order statement in the section called “RRset Ordering”). The client resolver code should rearrange the RRs as appropriate, that is, using any addresses on the local net in preference to other addresses. However, not all resolvers can do this or are correctly configured. When a client is using a local server, the sorting can be performed in the server, based on the client's address. This only requires configuring the name servers, not all the clients.
The sortlist statement (see below) takes an address_match_list and interprets it even more specifically than the topology statement does (the section called “Topology”). Each top level statement in the sortlist must itself be an explicit address_match_list with one or two elements. The first element (which may be an IP address, an IP prefix, an ACL name or a nested address_match_list) of each top level list is checked against the source address of the query until a match is found.
Once the source address of the query has been matched, if the top level statement contains only one element, the actual primitive element that matched the source address is used to select the address in the response to move to the beginning of the response. If the statement is a list of two elements, then the second element is treated the same as the address_match_list in a topology statement. Each top level element is assigned a distance and the address in the response with the minimum distance is moved to the beginning of the response.
In the following example, any queries received from any of the addresses of the host itself will get responses preferring addresses on any of the locally connected networks. Next most preferred are addresses on the 192.168.1/24 network, and after that either the 192.168.2/24 or 192.168.3/24 network with no preference shown between these two networks. Queries received from a host on the 192.168.1/24 network will prefer other addresses on that network to the 192.168.2/24 and 192.168.3/24 networks. Queries received from a host on the 192.168.4/24 or the 192.168.5/24 network will only prefer other addresses on their directly connected networks.
sortlist {
{ localhost; // IF the local host
{ localnets; // THEN first fit on the
192.168.1/24; // following nets
{ 192.168.2/24; 192.168.3/24; }; }; };
{ 192.168.1/24; // IF on class C 192.168.1
{ 192.168.1/24; // THEN use .1, or .2 or .3
{ 192.168.2/24; 192.168.3/24; }; }; };
{ 192.168.2/24; // IF on class C 192.168.2
{ 192.168.2/24; // THEN use .2, or .1 or .3
{ 192.168.1/24; 192.168.3/24; }; }; };
{ 192.168.3/24; // IF on class C 192.168.3
{ 192.168.3/24; // THEN use .3, or .1 or .2
{ 192.168.1/24; 192.168.2/24; }; }; };
{ { 192.168.4/24; 192.168.5/24; }; // if .4 or .5, prefer that net
};
};
The following example will give reasonable behavior for the local host and hosts on directly connected networks. It is similar to the behavior of the address sort in BIND 4.9.x. Responses sent to queries from the local host will favor any of the directly connected networks. Responses sent to queries from any other hosts on a directly connected network will prefer addresses on that same network. Responses to other queries will not be sorted.
sortlist {
{ localhost; localnets; };
{ localnets; };
};
When multiple records are returned in an answer it may be useful to configure the order of the records placed into the response. The rrset-order statement permits configuration of the ordering of the records in a multiple record response. See also the sortlist statement, the section called “The sortlist Statement”.
An order_spec is defined as follows:
[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 "*" (asterisk).
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.
The rrset-order statement is not yet fully implemented in BIND 9. BIND 9 currently does not fully support "fixed" ordering.
Sets the number of seconds to cache a
lame server indication. 0 disables caching. (This is
NOT recommended.)
The default is 600 (10 minutes) and the
maximum value is
1800 (30 minutes).
Lame-ttl also controls the amount of time DNSSEC validation failures are cached. There is a minimum of 30 seconds applied to bad cache entries if the lame-ttl is set to less than 30 seconds.
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.
Sets the maximum time for which the server will cache ordinary (positive) answers. The default is one week (7 days). A value of zero may cause all queries to return SERVFAIL, because of lost caches of intermediate RRsets (such as NS and glue AAAA/A records) in the resolution process.
The minimum number of root servers that
is required for a request for the root servers to be
accepted. The default
is 2.
Not implemented in BIND 9.
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.
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.
Sets the advertised EDNS UDP buffer size in bytes to control the size of packets received. 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 is to get UDP answers to pass through broken firewalls that block fragmented packets and/or block UDP packets that are greater than 512 bytes.
Sets the maximum EDNS UDP message size named will send in bytes. Valid values are 512 to 4096 (values outside this range will be silently adjusted). The default value is 4096. The usual reason for setting max-udp-size to a non-default value is to get UDP answers to pass through broken firewalls that block fragmented packets and/or block UDP packets that are greater than 512 bytes. This is independent of the advertised receive buffer (edns-udp-size).
Specifies
the file format of zone files (see
the section called “Additional File Formats”).
The default value is text, which is the
standard textual representation. Files in other formats
than text are typically expected
to be generated by the named-compilezone tool.
Note that when a zone file in a different format than
text is loaded, named
may omit some of the checks which would be performed for a
file in the text format. In particular,
check-names checks do not apply
for the raw format. This means
a zone file in the raw format
must be generated with the same check level as that
specified in the named configuration
file. This statement sets the
masterfile-format for all zones,
but can be overridden on a per-zone or per-view basis
by including a masterfile-format
statement within the zone or
view block in the configuration
file.
These set the initial value (minimum) and maximum number of recursive simultaneous clients for any given query (<qname,qtype,qclass>) that the server will accept before dropping additional clients. named will attempt to self tune this value and changes will be logged. The default values are 10 and 100.
This value should reflect how many queries come in for a given name in the time it takes to resolve that name. If the number of queries exceed this value, named will assume that it is dealing with a non-responsive zone and will drop additional queries. If it gets a response after dropping queries, it will raise the estimate. The estimate will then be lowered in 20 minutes if it has remained unchanged.
If clients-per-query is set to zero, then there is no limit on the number of clients per query and no queries will be dropped.
If max-clients-per-query is set to zero, then there is no upper bound other than imposed by recursive-clients.
The delay, in seconds, between sending sets of notify messages for a zone. The default is zero.
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.
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.
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 the gethostname() function. 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.
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 the gethostname() function.
The default server-id is none.
Named has some built-in empty zones (SOA and NS records only). These are for zones that should normally be answered locally and which queries should not be sent to the Internet's root servers. The official servers which cover these namespaces return NXDOMAIN responses to these queries. In particular, these cover the reverse namespace for addresses from RFC 1918 and RFC 3330. They also include the reverse namespace for IPv6 local address (locally assigned), IPv6 link local addresses, the IPv6 loopback address and the IPv6 unknown addresss.
Named will attempt to determine if a built-in zone already exists or is active (covered by a forward-only forwarding declaration) and will not create an empty zone in that case.
The current list of empty zones is:
Empty zones are settable at the view level and only apply to views of class IN. Disabled empty zones are only inherited from options if there are no disabled empty zones specified at the view level. To override the options list of disabled zones, you can disable the root zone at the view level, for example:
disable-empty-zone ".";
If you are using the address ranges covered here, you should already have reverse zones covering the addresses you use. In practice this appears to not be the case with many queries being made to the infrastructure servers for names in these spaces. So many in fact that sacrificial servers were needed to be deployed to channel the query load away from the infrastructure servers.
Specify what server name will appear in the returned SOA record for empty zones. If none is specified, then the zone's name will be used.
Specify what contact name will appear in the returned SOA record for empty zones. If none is specified, then "." will be used.
Enable or disable all empty zones. By default, they are enabled.
Disable individual empty zones. By default, none are disabled. This option can be specified multiple times.
The statistics file generated by BIND 9 is similar, but not identical, to that generated by BIND 8.
The statistics dump begins with a line, like:
+++ Statistics Dump +++ (973798949)
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 where the number is identical to the number in the beginning line; for example:
--- Statistics Dump --- (973798949)
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. |
|
duplicate |
The number of queries which the server attempted to recurse but discover an existing query with the same IP address, port, query id, name, type and class already being processed. |
|
dropped |
The number of queries for which the server discovered an excessive number of existing recursive queries for the same name, type and class and were subsequently dropped. |
Each query received by the server will cause exactly one of success, referral, nxrrset, nxdomain, failure, duplicate, or dropped to be incremented, and may additionally cause the recursion counter to be incremented.
The additional section cache, also called acache, is an internal cache to improve the response performance of BIND 9. When additional section caching is enabled, BIND 9 will cache an internal short-cut to the additional section content for each answer RR. Note that acache is an internal caching mechanism of BIND 9, and is not related to the DNS caching server function.
Additional section caching does not change the response content (except the RRsets ordering of the additional section, see below), but can improve the response performance significantly. It is particularly effective when BIND 9 acts as an authoritative server for a zone that has many delegations with many glue RRs.
In order to obtain the maximum performance improvement from additional section caching, setting additional-from-cache to no is recommended, since the current implementation of acache does not short-cut of additional section information from the DNS cache data.
One obvious disadvantage of acache is that it requires much more memory for the internal cached data. Thus, if the response performance does not matter and memory consumption is much more critical, the acache mechanism can be disabled by setting acache-enable to no. It is also possible to specify the upper limit of memory consumption for acache by using max-acache-size.
Additional section caching also has a minor effect on the RRset ordering in the additional section. Without acache, cyclic order is effective for the additional section as well as the answer and authority sections. However, additional section caching fixes the ordering when it first caches an RRset for the additional section, and the same ordering will be kept in succeeding responses, regardless of the setting of rrset-order. The effect of this should be minor, however, since an RRset in the additional section typically only contains a small number of RRs (and in many cases it only contains a single RR), in which case the ordering does not matter much.
The following is a summary of options related to acache.
If yes, additional section caching is enabled. The default value is no.
The server will remove stale cache entries, based on an LRU based algorithm, every acache-cleaning-interval minutes. The default is 60 minutes. If set to 0, no periodic cleaning will occur.
The maximum amount of memory in bytes to use for the server's acache.
When the amount of data in the acache reaches this limit,
the server
will clean more aggressively so that the limit is not
exceeded.
In a server with multiple views, the limit applies
separately to the
acache of each view.
The default is unlimited,
meaning that
entries are purged from the acache only at the
periodic cleaning time.
serverip_addr[/prefixlen]{ [ bogusyes_or_no; ] [ provide-ixfryes_or_no; ] [ request-ixfryes_or_no; ] [ ednsyes_or_no; ] [ edns-udp-sizenumber; ] [ max-udp-sizenumber; ] [ transfersnumber; ] [ transfer-format( one-answer | many-answers ); ]] [ keys{ string ; [ string ; [...]] }; ] [ transfer-source (ip4_addr|*) [portip_port] ; ] [ transfer-source-v6 (ip6_addr|*) [portip_port] ; ] [ notify-source (ip4_addr|*) [portip_port] ; ] [ notify-source-v6 (ip6_addr|*) [portip_port] ; ] [ query-source [ address (ip_addr|*) ] [ port (ip_port|*) ]; ] [ query-source-v6 [ address (ip_addr|*) ] [ port (ip_port|*) ]; ] };
The server statement defines
characteristics
to be associated with a remote name server. If a prefix length is
specified, then a range of servers is covered. Only the most
specific
server clause applies regardless of the order in
named.conf.
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 edns-udp-size option sets the EDNS UDP size that is advertised by named when querying the remote server. Valid values are 512 to 4096 bytes (values outside this range will be silently adjusted). This option is useful when you wish to advertises a different value to this server than the value you advertise globally, for example, when there is a firewall at the remote site that is blocking large replies.
The max-udp-size option sets the maximum EDNS UDP message size named will send. Valid values are 512 to 4096 bytes (values outside this range will be silently adjusted). This option is useful when you know that there is a firewall that is blocking large replies from named.
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. For more details, see the description of transfer-source and transfer-source-v6 in the section called “Zone Transfers”.
The notify-source and notify-source-v6 clauses specify the IPv4 and IPv6 source address to be used for notify messages sent to remote servers, respectively. For an IPv4 remote server, only notify-source can be specified. Similarly, for an IPv6 remote server, only notify-source-v6 can be specified.
The query-source and query-source-v6 clauses specify the IPv4 and IPv6 source address to be used for queries sent to remote servers, respectively. For an IPv4 remote server, only query-source can be specified. Similarly, for an IPv6 remote server, only query-source-v6 can be specified.
trusted-keys {stringnumbernumbernumberstring; [stringnumbernumbernumberstring; [...]] };
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.
All keys (and corresponding zones) listed in trusted-keys are deemed to exist regardless of what parent zones say. Similarly for all keys listed in trusted-keys only those keys are used to validate the DNSKEY RRset. The parent's DS RRset will not be used.
The trusted-keys statement can contain multiple key entries, each consisting of the key's domain name, flags, protocol, algorithm, and the Base-64 representation of the key data.
viewview_name[class] { match-clients {address_match_list}; match-destinations {address_match_list}; match-recursive-onlyyes_or_no; [view_option; ...] [zone_statement; ...] };
The view statement is a powerful 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 only be accessible to clients that match the view. By defining a zone of the same name in multiple views, different zone data can be given to different clients, for example, "internal" and "external" clients in a split DNS setup.
Many of the options given in the options statement can also be used within a view statement, and then apply only when resolving queries with that view. When no view-specific value is given, the value in the options statement is used as a default. Also, zone options can have default values specified in the view statement; these view-specific defaults take precedence over those in the options statement.
Views are class specific. If no class is given, class IN is assumed. Note that all non-IN views must contain a hint zone, since only the IN class has compiled-in default hints.
If there are no view statements in the config file, a default view that matches any client is automatically created in class IN. Any zone statements specified on the top level of the configuration file are considered to be part of this default view, and the options statement will apply to the default view. If any explicit view statements are present, all zone statements must occur inside view statements.
Here is an example of a typical split DNS setup implemented using view statements:
view "internal" {
// This should match our internal networks.
match-clients { 10.0.0.0/8; };
// Provide recursive service to internal clients only.
recursion yes;
// Provide a complete view of the example.com zone
// including addresses of internal hosts.
zone "example.com" {
type master;
file "example-internal.db";
};
};
view "external" {
// Match all clients not matched by the previous view.
match-clients { any; };
// Refuse recursive service to external clients.
recursion no;
// Provide a restricted view of the example.com zone
// containing only publicly accessible hosts.
zone "example.com" {
type master;
file "example-external.db";
};
};
zonezone_name[class] { type master; [ allow-query {address_match_list}; ] [ allow-transfer {address_match_list}; ] [ allow-update {address_match_list}; ] [ update-policy {update_policy_rule[...] }; ] [ also-notify {ip_addr[portip_port] ; [ip_addr[portip_port] ; ... ] }; ] [ check-names (warn|fail|ignore) ; ] [ check-mx (warn|fail|ignore) ; ] [ check-wildcardyes_or_no; ] [ check-integrityyes_or_no; ] [ dialupdialup_option; ] [ filestring; ] [ masterfile-format (text|raw) ; ] [ journalstring; ] [ max-journal-sizesize_spec; ] [ forward (only|first) ; ] [ forwarders { [ip_addr[portip_port] ; ... ] }; ] [ ixfr-basestring; ] [ ixfr-from-differencesyes_or_no; ] [ ixfr-tmp-filestring; ] [ maintain-ixfr-baseyes_or_no; ] [ max-ixfr-log-sizenumber; ] [ max-transfer-idle-outnumber; ] [ max-transfer-time-outnumber; ] [ notifyyes_or_no|explicit|master-only; ] [ notify-delayseconds; ] [ pubkeynumbernumbernumberstring; ] [ notify-source (ip4_addr|*) [portip_port] ; ] [ notify-source-v6 (ip6_addr|*) [portip_port] ; ] [ zone-statisticsyes_or_no; ] [ sig-validity-intervalnumber; ] [ databasestring; ] [ min-refresh-timenumber; ] [ max-refresh-timenumber; ] [ min-retry-timenumber; ] [ max-retry-timenumber; ] [ key-directorypath_name; ] [ zero-no-soa-ttlyes_or_no; ] }; zonezone_name[class] { type slave; [ allow-notify {address_match_list}; ] [ allow-query {address_match_list}; ] [ allow-transfer {address_match_list}; ] [ allow-update-forwarding {address_match_list}; ] [ update-check-kskyes_or_no; ] [ also-notify {ip_addr[portip_port] ; [ip_addr[portip_port] ; ... ] }; ] [ check-names (warn|fail|ignore) ; ] [ dialupdialup_option; ] [ filestring; ] [ masterfile-format (text|raw) ; ] [ journalstring; ] [ max-journal-sizesize_spec; ] [ forward (only|first) ; ] [ forwarders { [ip_addr[portip_port] ; ... ] }; ] [ ixfr-basestring; ] [ ixfr-from-differencesyes_or_no; ] [ ixfr-tmp-filestring; ] [ maintain-ixfr-baseyes_or_no; ] [ masters [portip_port] { (masters_list|ip_addr[portip_port] [keykey] ) ; [...] }; ] [ max-ixfr-log-sizenumber; ] [ max-transfer-idle-innumber; ] [ max-transfer-idle-outnumber; ] [ max-transfer-time-innumber; ] [ max-transfer-time-outnumber; ] [ notifyyes_or_no|explicit|master-only; ] [ pubkeynumbernumbernumberstring; ] [ transfer-source (ip4_addr|*) [portip_port] ; ] [ transfer-source-v6 (ip6_addr|*) [portip_port] ; ] [ alt-transfer-source (ip4_addr|*) [portip_port] ; ] [ alt-transfer-source-v6 (ip6_addr|*) [portip_port] ; ] [ use-alt-transfer-sourceyes_or_no; ] [ notify-source (ip4_addr|*) [portip_port] ; ] [ notify-source-v6 (ip6_addr|*) [portip_port] ; ] [ zone-statisticsyes_or_no; ] [ databasestring; ] [ min-refresh-timenumber; ] [ max-refresh-timenumber; ] [ min-retry-timenumber; ] [ max-retry-timenumber; ] [ multi-masteryes_or_no; ] [ zero-no-soa-ttlyes_or_no; ] }; zonezone_name[class] { type hint; filestring; [ delegation-onlyyes_or_no; ] [ check-names (warn|fail|ignore) ; // Not Implemented. ] }; zonezone_name[class] { type stub; [ allow-query {address_match_list}; ] [ check-names (warn|fail|ignore) ; ] [ dialupdialup_option; ] [ delegation-onlyyes_or_no; ] [ filestring; ] [ masterfile-format (text|raw) ; ] [ forward (only|first) ; ] [ forwarders { [ip_addr[portip_port] ; ... ] }; ] [ masters [portip_port] { (masters_list|ip_addr[portip_port] [keykey] ) ; [...] }; ] [ max-transfer-idle-innumber; ] [ max-transfer-time-innumber; ] [ pubkeynumbernumbernumberstring; ] [ transfer-source (ip4_addr|*) [portip_port] ; ] [ transfer-source-v6 (ip6_addr|*) [portip_port] ; ] [ alt-transfer-source (ip4_addr|*) [portip_port] ; ] [ alt-transfer-source-v6 (ip6_addr|*) [portip_port] ; ] [ use-alt-transfer-sourceyes_or_no; ] [ zone-statisticsyes_or_no; ] [ databasestring; ] [ min-refresh-timenumber; ] [ max-refresh-timenumber; ] [ min-retry-timenumber; ] [ max-retry-timenumber; ] [ multi-masteryes_or_no; ] }; zonezone_name[class] { type forward; [ forward (only|first) ; ] [ forwarders { [ip_addr[portip_port] ; ... ] }; ] [ delegation-onlyyes_or_no; ] }; zonezone_name[class] { type delegation-only; };
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The server has a master copy of the data for the zone and will be able to provide authoritative answers for it. |
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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 startup 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 filenames. For
example,
a slave server for the zone |
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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
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
RFC1918 addressing may be configured with stub zones
for
|
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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. |
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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. |
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This is used to enforce the delegation-only status of infrastructure zones (e.g. COM, NET, ORG). Any answer that is received without an 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.
See caveats in root-delegation-only. |
The zone's name may optionally be followed by a class. If
a class is not specified, class IN (for Internet),
is assumed. This is correct for the vast majority of cases.
The hesiod class is
named for an information service from MIT's Project Athena. It
is
used to share information about various systems databases, such
as users, groups, printers and so on. The 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.
See the description of allow-notify in the section called “Access Control”.
See the description of allow-query in the section called “Access Control”.
See the description of allow-transfer in the section called “Access Control”.
See the description of allow-update in the section called “Access Control”.
Specifies a "Simple Secure Update" policy. See the section called “Dynamic Update Policies”.
See the description of allow-update-forwarding in the section called “Access Control”.
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.
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.
See the description of check-mx in the section called “Boolean Options”.
See the description of check-wildcard in the section called “Boolean Options”.
See the description of check-integrity in the section called “Boolean Options”.
See the description of check-sibling in the section called “Boolean Options”.
See the description of zero-no-soa-ttl in the section called “Boolean Options”.
See the description of update-check-ksk in the section called “Boolean Options”.
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.
See the description of dialup in the section called “Boolean Options”.
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.
See caveats in root-delegation-only.
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.
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 and the global options are not used.
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.
Was an undocumented option in BIND 8. Ignored in BIND 9.
Allow the default journal's filename to be overridden.
The default is the zone's filename with ".jnl" appended.
This is applicable to master and slave zones.
See the description of max-journal-size in the section called “Server Resource Limits”.
See the description of max-transfer-time-in in the section called “Zone Transfers”.
See the description of max-transfer-idle-in in the section called “Zone Transfers”.
See the description of max-transfer-time-out in the section called “Zone Transfers”.
See the description of max-transfer-idle-out in the section called “Zone Transfers”.
See the description of notify in the section called “Boolean Options”.
See the description of notify-delay in the section called “Tuning”.
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.
If yes, the server will keep
statistical
information for this zone, which can be dumped to the
statistics-file defined in
the server options.
See the description of sig-validity-interval in the section called “Tuning”.
See the description of transfer-source in the section called “Zone Transfers”.
See the description of transfer-source-v6 in the section called “Zone Transfers”.
See the description of alt-transfer-source in the section called “Zone Transfers”.
See the description of alt-transfer-source-v6 in the section called “Zone Transfers”.
See the description of use-alt-transfer-source in the section called “Zone Transfers”.
See the description of notify-source in the section called “Zone Transfers”.
See the description of notify-source-v6 in the section called “Zone Transfers”.
See the description in the section called “Tuning”.
See the description of
ixfr-from-differences in the section called “Boolean Options”.
(Note that the ixfr-from-differences
master and
slave choices are not
available at the zone level.)
See the description of key-directory in the section called “options Statement Definition and Usage”.
See the description of multi-master in the section called “Boolean Options”.
See the description of masterfile-format in the section called “Tuning”.
BIND 9 supports two alternative methods of granting clients the right to perform dynamic updates to a zone, configured by the allow-update and update-policy option, respectively.
The allow-update clause works the same way as in previous versions of BIND. It grants given clients the permission to update any record of any name in the zone.
The update-policy clause is new in BIND 9 and allows more fine-grained control over what updates are allowed. A set of rules is specified, where each rule either grants or denies permissions for one or more names to be updated by one or more identities. If the dynamic update request message is signed (that is, it includes either a TSIG or SIG(0) record), the identity of the signer can be determined.
Rules are specified in the update-policy zone option, and are only meaningful for master zones. When the update-policy statement is present, it is a configuration error for the allow-update statement to be present. The update-policy statement only examines the signer of a message; the source address is not relevant.
This is how a rule definition looks:
( grant | deny )identitynametypename[types]
Each rule grants or denies privileges. Once a message has successfully matched a rule, the operation is immediately granted or denied and no further rules are examined. A rule is matched when the signer matches the identity field, the name matches the name field in accordance with the nametype field, and the type matches the types specified in the type field.
The identity field specifies a name or a wildcard name.
Normally, this
is the name of the TSIG or SIG(0) key used to sign the update
request. When a
TKEY exchange has been used to create a shared secret, the
identity of the
shared secret is the same as the identity of the key used to
authenticate the
TKEY exchange. When the identity field specifies a
wildcard name, it is subject to DNS wildcard expansion, so the
rule will apply
to multiple identities. The identity field must
contain a fully-qualified domain name.
The nametype field has 6
values:
name, subdomain,
wildcard, self,
selfsub, and selfwild.
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Exact-match semantics. This rule matches
when the name being updated is identical
to the contents of the
|
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This rule matches when the name being updated
is a subdomain of, or identical to, the
contents of the |
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The |
|
|
This rule matches when the name being updated
matches the contents of the
|
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This rule is similar to |
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This rule is similar to |
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 RRSIG, NS, SOA, and NSEC. Types may be specified by name, including "ANY" (ANY matches all types except NSEC, which can never be updated). Note that when an attempt is made to delete all records associated with a name, the rules are checked for each existing record type.
This section, largely borrowed from RFC 1034, describes the concept of a Resource Record (RR) and explains when each is used. Since the publication of RFC 1034, several new RRs have been identified and implemented in the DNS. These are also included.
A domain name identifies a node. Each node has a set of resource information, which may be empty. The set of resource information associated with a particular name is composed of separate RRs. The order of RRs in a set is not significant and need not be preserved by name servers, resolvers, or other parts of the DNS. However, sorting of multiple RRs is permitted for optimization purposes, for example, to specify that a particular nearby server be tried first. See the section called “The sortlist Statement” and the section called “RRset Ordering”.
The components of a Resource Record are:
|
owner name |
The domain name where the RR is found. |
|
type |
An encoded 16-bit value that specifies 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. |
|
DNSKEY |
Stores a public key associated with a signed DNS zone. Described in RFC 4034. |
|
DS |
Stores the hash of a public key associated with a signed DNS zone. Described in RFC 4034. |
|
GPOS |
Specifies the global position. Superseded by LOC. |
|
HINFO |
Identifies the CPU and OS used by a host. Described in RFC 1035. |
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IPSECKEY |
Provides a method for storing IPsec keying material in DNS. Described in RFC 4025. |
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ISDN |
Representation of ISDN addresses. Experimental. Described in RFC 1183. |
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KEY |
Stores a public key associated with a DNS name. Used in original DNSSEC; replaced by DNSKEY in DNSSECbis, but still used with SIG(0). Described in RFCs 2535 and 2931. |
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KX |
Identifies a key exchanger for this DNS name. Described in RFC 2230. |
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LOC |
For storing GPS info. Described in RFC 1876. Experimental. |
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MX |
Identifies a mail exchange for the domain with a 16-bit preference value (lower is better) followed by the host name of the mail exchange. Described in RFC 974, RFC 1035. |
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NAPTR |
Name authority pointer. Described in RFC 2915. |
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NSAP |
A network service access point. Described in RFC 1706. |
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NS |
The authoritative name server for the domain. Described in RFC 1035. |
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NSEC |
Used in DNSSECbis 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 4034. |
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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. Used in original DNSSEC; replaced by NSEC in DNSSECbis. Described in RFC 2535. |
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PTR |
A pointer to another part of the domain name space. Described in RFC 1035. |
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PX |
Provides mappings between RFC 822 and X.400 addresses. Described in RFC 2163. |
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RP |
Information on persons responsible for the domain. Experimental. Described in RFC 1183. |
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RRSIG |
Contains DNSSECbis signature data. Described in RFC 4034. |
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RT |
Route-through binding for hosts that do not have their own direct wide area network addresses. Experimental. Described in RFC 1183. |
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SIG |
Contains DNSSEC signature data. Used in original DNSSEC; replaced by RRSIG in DNSSECbis, but still used for SIG(0). Described in RFCs 2535 and 2931. |
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SOA |
Identifies the start of a zone of authority. Described in RFC 1035. |
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SPF |
Contains the Sender Policy Framework information for a given email domain. Described in RFC 4408. |
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SRV |
Information about well known network services (replaces WKS). Described in RFC 2782. |
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SSHFP |
Provides a way to securly publish a secure shell key's fingerprint. Described in RFC 4255. |
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TXT |
Text records. Described in RFC 1035. |
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WKS |
Information about which well known network services, such as SMTP, that a domain supports. Historical. |
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X25 |
Representation of X.25 network addresses. Experimental. Described in RFC 1183. |
The following classes of resource records are currently valid in the DNS:
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IN |
The Internet. |
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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.,
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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.
RRs are represented in binary form in the packets of the DNS protocol, and are usually represented in highly encoded form when stored in a name server or resolver. In the examples provided in RFC 1034, a style similar to that used in master files was employed in order to show the contents of RRs. In this format, most RRs are shown on a single line, although continuation lines are possible using parentheses.
The start of the line gives the owner of the RR. If a line begins with a blank, then the owner is assumed to be the same as that of the previous RR. Blank lines are often included for readability.
Following the owner, we list the TTL, type, and class of the RR. Class and type use the mnemonics defined above, and TTL is an integer before the type field. In order to avoid ambiguity in parsing, type and class mnemonics are disjoint, TTLs are integers, and the type mnemonic is always last. The IN class and TTL values are often omitted from examples in the interests of clarity.
The resource data or RDATA section of the RR are given using knowledge of the typical representation for the data.
For example, we might show the RRs carried in a message as:
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The MX RRs have an RDATA section which consists of a 16-bit number followed by a domain name. The address RRs use a standard IP address format to contain a 32-bit internet address.
The above example shows six RRs, with two RRs at each of three domain names.
Similarly we might see:
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This example shows two addresses for
XX.LCS.MIT.EDU, each of a different class.
As described above, domain servers store information as a series of resource records, each of which contains a particular piece of information about a given domain name (which is usually, but not always, a host). The simplest way to think of a RR is as a typed pair of data, a domain name matched with a relevant datum, and stored with some additional type information to help systems determine when the RR is relevant.
MX records are used to control delivery of email. The data specified in the record is a priority and a domain name. The priority controls the order in which email delivery is attempted, with the lowest number first. If two priorities are the same, a server is chosen randomly. If no servers at a given priority are responding, the mail transport agent will fall back to the next largest priority. Priority numbers do not have any absolute meaning — they are relevant only respective to other MX records for that domain name. The domain name given is the machine to which the mail will be delivered. It must have an associated address record (A or AAAA) — 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. For example:
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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.
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.
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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). |
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$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. |
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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.
Reverse name resolution (that is, translation from IP address to name) is achieved by means of the in-addr.arpa domain and PTR records. Entries in the in-addr.arpa domain are made in least-to-most significant order, read left to right. This is the opposite order to the way IP addresses are usually written. Thus, a machine with an IP address of 10.1.2.3 would have a corresponding in-addr.arpa name of 3.2.1.10.in-addr.arpa. This name should have a PTR resource record whose data field is the name of the machine or, optionally, multiple PTR records if the machine has more than one name. For example, in the [example.com] domain:
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The $ORIGIN lines in the examples are for providing context to the examples only — they do not necessarily appear in the actual usage. They are only used here to indicate that the example is relative to the listed origin.
The Master File Format was initially defined in RFC 1035 and has subsequently been extended. While the Master File Format itself is class independent all records in a Master File must be of the same class.
Master File Directives include $ORIGIN, $INCLUDE, and $TTL.
Syntax: $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.
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.
RFC 1035 specifies that the current origin should be restored after an $INCLUDE, but it is silent on whether the current domain name should also be restored. BIND 9 restores both of them. This could be construed as a deviation from RFC 1035, a feature, or both.
Syntax: $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.
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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. |
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lhs |
This describes the owner name of the resource records to be created. Any single $ (dollar sign) symbols within the lhs string 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 { (left brace) immediately following the $ as ${offset[,width[,base]]}. For example, ${-20,3,d} subtracts 20 from the current value, prints the result as a decimal in a zero-padded field of width 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 as indicating a literal $ in the output. |
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ttl |
Specifies the time-to-live 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. |
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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. |
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type |
At present the only supported types are PTR, CNAME, DNAME, A, AAAA and NS. |
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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.
In addition to the standard textual format, BIND 9
supports the ability to read or dump to zone files in
other formats. The raw format is
currently available as an additional format. It is a
binary format representing BIND 9's internal data
structure directly, thereby remarkably improving the
loading time.
For a primary server, a zone file in the
raw format is expected to be
generated from a textual zone file by the
named-compilezone command. For a
secondary server or for a dynamic zone, it is automatically
generated (if this format is specified by the
masterfile-format option) when
named dumps the zone contents after
zone transfer or when applying prior updates.
If a zone file in a binary format needs manual modification, it first must be converted to a textual form by the named-compilezone command. All necessary modification should go to the text file, which should then be converted to the binary form by the named-compilezone command again.
Although the raw format uses the
network byte order and avoids architecture-dependent
data alignment so that it is as much portable as
possible, it is primarily expected to be used inside
the same single system. In order to export a zone
file in the raw format or make a
portable backup of the file, it is recommended to
convert the file to the standard textual representation.