4. BIND 9 Configuration Reference¶
4.1. Configuration File Elements¶
Following is a list of elements used throughout the BIND configuration file documentation:
acl_name¶The name of an
address_match_listas defined by theaclstatement.address_match_list¶A list of one or more
ip_addr,ip_prefix,key_id, oracl_nameelements; see Address Match Lists.primaries_list¶A named list of one or more
ip_addrwith optionaltls_id,key_idand/orip_port. Aprimaries_listmay include otherprimaries_list.domain_name¶A quoted string which is used as a DNS name; for example.
my.test.domain.namelist¶A list of one or more
domain_nameelements.dotted_decimal¶One to four integers valued 0 through 255 separated by dots (
.), such as123.45.67or89.123.45.67.ip4_addr¶An IPv4 address with exactly four elements in
dotted_decimalnotation.ip6_addr¶An IPv6 address, such as
2001:db8::1234. IPv6-scoped addresses that have ambiguity on their scope zones must be disambiguated by an appropriate zone ID with the percent character (%) as a delimiter. It is strongly recommended to use string zone names rather than numeric identifiers, to be robust against system configuration changes. However, since there is no standard mapping for such names and identifier values, only interface names as link identifiers are supported, assuming one-to-one mapping between interfaces and links. For example, a link-local addressfe80::1on the link attached to the interfacene0can be specified asfe80::1%ne0. Note that on most systems link-local addresses always have ambiguity and need to be disambiguated.ip_addr¶An
ip4_addrorip6_addr.ip_dscp¶A
numberbetween 0 and 63, used to select a differentiated services code point (DSCP) value for use with outgoing traffic on operating systems that support DSCP.ip_port¶An IP port
number. Thenumberis limited to 0 through 65535, with values below 1024 typically restricted to use by processes running as root. In some cases, an asterisk (*) character can be used as a placeholder to select a random high-numbered port.ip_prefix¶An IP network specified as an
ip_addr, followed by a slash (/) and then the number of bits in the netmask. Trailing zeros in an``ip_addr`` may be omitted. For example,127/8is the network127.0.0.0``with netmask ``255.0.0.0and1.2.3.0/28is network1.2.3.0with netmask255.255.255.240. When specifying a prefix involving a IPv6-scoped address, the scope may be omitted. In that case, the prefix matches packets from any scope.key_id¶A
domain_namerepresenting the name of a shared key, to be used for transaction security.key_list¶A list of one or more
key_id, separated by semicolons and ending with a semicolon.tls_id¶A string representing a TLS configuration object, including a key and certificate.
number¶A non-negative 32-bit integer (i.e., a number between 0 and 4294967295, inclusive). Its acceptable value might be further limited by the context in which it is used.
fixedpoint¶A non-negative real number that can be specified to the nearest one-hundredth. Up to five digits can be specified before a decimal point, and up to two digits after, so the maximum value is 99999.99. Acceptable values might be further limited by the contexts in which they are used.
path_name¶A quoted string which is used as a pathname, such as
zones/master/my.test.domain.port_list¶A list of an
ip_portor a port range. A port range is specified in the form ofrangefollowed by twoip_port``s, ``port_lowandport_high, which represents port numbers fromport_lowthroughport_high, inclusive.port_lowmust not be larger thanport_high. For example,range 1024 65535represents ports from 1024 through 65535. In either case an asterisk (*) character is not allowed as a validip_port.size_spec¶A 64-bit unsigned integer, or the keywords
unlimitedordefault. Integers may take values 0 <= value <= 18446744073709551615, though certain parameters (such asmax-journal-size) may use a more limited range within these extremes. In most cases, setting a value to 0 does not literally mean zero; it means “undefined” or “as big as possible,” depending on the context. See the explanations of particular parameters that usesize_specfor details on how they interpret its use. Numeric values can optionally be followed by a scaling factor:Korkfor kilobytes,Mormfor megabytes, andGorgfor gigabytes, which scale by 1024, 1024*1024, and 1024*1024*1024 respectively.unlimitedgenerally means “as big as possible,” and is usually the best way to safely set a very large number.defaultuses the limit that was in force when the server was started.size_or_percent¶A
size_specor integer value followed by%to represent percent. The behavior is exactly the same assize_spec, butsize_or_percentalso allows specifying a positive integer value followed by the%sign to represent percent.yes_or_no¶Either
yesorno. The wordstrueandfalseare also accepted, as are the numbers1and0.dialup_option¶One of
yes,no,notify,notify-passive,refresh, orpassive. When used in a zone,notify-passive,refresh, andpassiveare restricted to secondary and stub zones.
4.1.1. Address Match Lists¶
4.1.1.1. Syntax¶
address_match_list = address_match_list_element ; ...
address_match_list_element = [ ! ] ( ip_address | ip_prefix |
key key_id | acl_name | { address_match_list } )
4.1.1.2. Definition and Usage¶
Address match lists are primarily used to determine access control for
various server operations. They are also used in the listen-on and
sortlist statements. The elements which constitute an address match
list can be any of the following:
an IP address (IPv4 or IPv6)
an IP prefix (in
/notation)a key ID, as defined by the
keystatementthe name of an address match list defined with the
aclstatementa nested address match list enclosed in braces
Elements can be negated with a leading exclamation mark (!), and the
match list names “any”, “none”, “localhost”, and “localnets” are
predefined. More information on those names can be found in the
description of the acl statement.
The addition of the key clause made the name of this syntactic element something of a misnomer, since security keys can be used to validate access without regard to a host or network address. Nonetheless, the term “address match list” is still used throughout the documentation.
When a given IP address or prefix is compared to an address match list, the comparison takes place in approximately O(1) time. However, key comparisons require that the list of keys be traversed until a matching key is found, and therefore may be somewhat slower.
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-recursion,
allow-recursion-on, allow-query, allow-query-on,
allow-query-cache, allow-query-cache-on, allow-transfer,
allow-update, allow-update-forwarding, blackhole, and
keep-response-order all use address match lists. Similarly, the
listen-on option causes the server to refuse queries on any of
the machine’s addresses which do not match the list.
Order of insertion is significant. If more than one element in an ACL is
found to match a given IP address or prefix, preference is given to
the one that came first in the ACL definition. Because of this
first-match behavior, 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
matches 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 blocking 1.2.3.13
via the negation, but all other 1.2.3.* hosts pass through.
4.1.2. Comment Syntax¶
The BIND 9 comment syntax allows 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.
4.1.2.1. Syntax¶
/* This is a BIND comment as in C */
// This is a BIND comment as in C++
# This is a BIND comment as in common Unix shells
# and perl
4.1.2.2. Definition and Usage¶
Comments may appear anywhere that whitespace may appear in a BIND configuration file.
C-style comments start with the two characters /* (slash, star) and end with */ (star, slash). Because they are completely delimited with these characters, they can be used to comment only a portion of a line or to span multiple lines.
C-style comments cannot be nested. For example, the following is not valid because the entire comment ends with the first */:
/* This is the start of a comment.
This is still part of the comment.
/* This is an incorrect attempt at nesting a comment. */
This is no longer in any comment. */
C++-style comments start with the two characters // (slash, slash) and continue to the end of the physical line. They cannot be continued across multiple physical lines; to have one logical comment span multiple lines, each line must use the // pair. For example:
// This is the start of a comment. The next line
// is a new comment, even though it is logically
// part of the previous comment.
Shell-style (or perl-style) comments start with the
character # (number sign) and continue to the end of the physical
line, as in C++ comments. For example:
# This is the start of a comment. The next line
# is a new comment, even though it is logically
# part of the previous comment.
Warning
The semicolon (;) character cannot start a comment, unlike
in a zone file. The semicolon indicates the end of a
configuration statement.
4.2. Configuration File Grammar¶
A BIND 9 configuration consists of statements and comments. Statements end with a semicolon; statements and comments are the only elements that can appear without enclosing braces. Many statements contain a block of sub-statements, which are also terminated with a semicolon.
The following statements are supported:
aclDefines a named IP address matching list, for access control and other uses.
controlsDeclares control channels to be used by the
rndcutility.dnssec-policyDescribes a DNSSEC key and signing policy for zones. See dnssec-policy Grammar for details.
includeIncludes a file.
keySpecifies key information for use in authentication and authorization using TSIG.
loggingSpecifies what information the server logs and where the log messages are sent.
mastersSynonym for
primaries.optionsControls global server configuration options and sets defaults for other statements.
primariesDefines a named list of servers for inclusion in stub and secondary zones’
primariesoralso-notifylists. (Note: this is a synonym for the original keywordmasters, which can still be used, but is no longer the preferred terminology.)serverSets certain configuration options on a per-server basis.
statistics-channelsDeclares communication channels to get access to
namedstatistics.tlsSpecifies configuration information for a TLS connection, including a
key-file,cert-file,ca-fileandhostname.trust-anchorsDefines DNSSEC trust anchors: if used with the
initial-keyorinitial-dskeyword, trust anchors are kept up-to-date using RFC 5011 trust anchor maintenance; if used withstatic-keyorstatic-ds, keys are permanent.managed-keysIs identical to
trust-anchors; this option is deprecated in favor oftrust-anchorswith theinitial-keykeyword, and may be removed in a future release.trusted-keysDefines permanent trusted DNSSEC keys; this option is deprecated in favor of
trust-anchorswith thestatic-keykeyword, and may be removed in a future release.viewDefines a view.
zoneDefines a zone.
The logging and options statements may only occur once per
configuration.
4.2.1. acl Statement Grammar¶
acl <string> { <address_match_element>; ... };
4.2.2. acl Statement Definition and Usage¶
The acl statement assigns a symbolic name to an address match list.
It gets its name from one of the primary uses of address match lists: Access
Control Lists (ACLs).
The following ACLs are built-in:
anyMatches all hosts.
noneMatches no hosts.
localhostMatches the IPv4 and IPv6 addresses of all network interfaces on the system. When addresses are added or removed, the
localhostACL element is updated to reflect the changes.localnetsMatches any host on an IPv4 or IPv6 network for which the system has an interface. When addresses are added or removed, the
localnetsACL element is updated to reflect the changes. Some systems do not provide a way to determine the prefix lengths of local IPv6 addresses; in such cases,localnetsonly matches the local IPv6 addresses, just likelocalhost.
4.2.3. controls Statement Grammar¶
controls {
inet ( <ipv4_address> | <ipv6_address> |
* ) [ port ( <integer> | * ) ] allow
{ <address_match_element>; ... } [
keys { <string>; ... } ] [ read-only
<boolean> ];
unix <quoted_string> perm <integer>
owner <integer> group <integer> [
keys { <string>; ... } ] [ read-only
<boolean> ];
};
4.2.4. controls Statement Definition and Usage¶
The controls statement declares control channels to be used by
system administrators to manage 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 are accepted on any of the system’s
IPv4 addresses. To listen on the IPv6 wildcard address, use an
ip_addr of ::. If rndc is only used 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 that 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_id``s. Each ``key_id in
the key_list is authorized to execute commands over the control
channel. See Administrative Tools for information about
configuring keys in rndc.
If the read-only clause is enabled, the control channel is limited
to the following set of read-only commands: nta -dump, null,
status, showzone, testgen, and zonestatus. By default,
read-only is not enabled and the control channel allows read-write
access.
If no controls statement is present, named sets 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 attempts
to load the command channel key from the file rndc.key in /etc
(or whatever sysconfdir was specified when BIND was built). To
create an rndc.key file, run rndc-confgen -a.
To disable the command channel, use an empty controls statement:
controls { };.
4.2.5. include Statement Grammar¶
include filename;
4.2.6. include Statement Definition and Usage¶
The include statement inserts the specified file (or files if a valid glob
expression is detected) 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.
4.2.7. key Statement Grammar¶
key <string> {
algorithm <string>;
secret <string>;
};
4.2.8. key Statement Definition and Usage¶
The key statement defines a shared secret key for use with TSIG (see
TSIG) or the command channel (see 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 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 that uniquely
identifies the key. It can be used in a server statement to cause
requests sent to that server to be signed with this key, or in address
match lists to verify that incoming requests have been signed with a key
matching this name, algorithm, and secret.
The algorithm_id is a string that specifies a security/authentication
algorithm. The named server 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 Base64-encoded string.
4.2.9. logging Statement Grammar¶
logging {
category <string> { <string>; ... };
channel <string> {
buffered <boolean>;
file <quoted_string> [ versions ( unlimited | <integer> ) ]
[ size <size> ] [ suffix ( increment | timestamp ) ];
null;
print-category <boolean>;
print-severity <boolean>;
print-time ( iso8601 | iso8601-utc | local | <boolean> );
severity <log_severity>;
stderr;
syslog [ <syslog_facility> ];
};
};
4.2.10. logging Statement Definition and Usage¶
The logging statement configures a wide variety of logging options
for the name server. Its channel phrase associates output methods,
format options, and severity levels with a name that can then be used
with the category phrase to select how various classes of messages
are logged.
Only one logging statement is used to define as many channels and
categories as desired. If there is no logging statement, the
logging configuration is:
logging {
category default { default_syslog; default_debug; };
category unmatched { null; };
};
If named is started with the -L option, it logs to the specified
file at startup, instead of using syslog. In this case the logging
configuration is:
logging {
category default { default_logfile; default_debug; };
category unmatched { null; };
};
The logging configuration is only established when the entire
configuration file has been parsed. When the server starts 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.
4.2.10.1. The channel Phrase¶
All log output goes to one or more channels; there is no limit to
the number of channels that can be created.
Every channel definition must include a destination clause that says
whether messages selected for the channel go to a file, go to a particular
syslog facility, go to the standard error stream, or are discarded. The definition can
optionally also limit the message severity level that is accepted
by the channel (the default is info), and whether to include a
named-generated time stamp, the category name, and/or the 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 additional arguments to specify how large the file is
allowed to become before it is rolled to a backup file (size), how
many backup versions of the file are saved each time this happens
(versions), and the format to use for naming backup versions
(suffix).
The size option is used to limit log file growth. If the file ever
exceeds the specified size, then named stops writing to the file
unless it has a versions option associated with it. If backup
versions are kept, the files are rolled as described below. If there is
no versions option, no more data is 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.
File rolling only occurs when the file exceeds the size specified with
the size option. No backup versions are kept by default; any
existing log file is simply appended. The versions option specifies
how many backup versions of the file should be kept. If set to
unlimited, there is no limit.
The suffix option can be set to either increment or
timestamp. If set to timestamp, then when a log file is rolled,
it is saved with the current timestamp as a file suffix. If set to
increment, then backup files are saved with incrementing numbers as
suffixes; older files are renamed when rolling. For example, if
versions is set to 3 and suffix to increment, then when
filename.log reaches the size specified by size,
filename.log.1 is renamed to filename.log.2, filename.log.0
is renamed to filename.log.1, and filename.log is renamed to
filename.log.0, whereupon a new filename.log is opened.
Here is an example using the size, versions, and suffix options:
channel an_example_channel {
file "example.log" versions 3 size 20m suffix increment;
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
handles messages sent to this facility is described in the
syslog.conf man page. On a system which uses a very old
version of syslog, which only uses two arguments to the openlog()
function, this clause is silently ignored.
On Windows machines, syslog messages are directed to the EventViewer.
The severity clause works like syslog’s “priorities,” except
that they can also be used when writing straight to a file rather
than using syslog. Messages which are not at least of the severity
level given are not selected for the channel; messages of higher
severity levels are accepted.
When using syslog, the syslog.conf priorities
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, causes 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, as when debugging a
configuration, for example.
The server can supply extensive debugging information when it is in
debugging mode. If the server’s global debug level is greater than zero,
debugging mode is 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;
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;
};
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.
print-time can be set to yes, no, or a time format
specifier, which may be one of local, iso8601, or
iso8601-utc. If set to no, the date and time are not
logged. If set to yes or local, the date and time are logged in
a human-readable format, using the local time zone. If set to
iso8601, the local time is logged in ISO 8601 format. If set to
iso8601-utc, the date and time are logged in ISO 8601 format,
with time zone set to UTC. The default is no.
print-time may be specified for a syslog channel, but it is
usually pointless since syslog also logs the date and time.
If print-category is requested, then the category of the message
is logged as well. Finally, if print-severity is on, then the
severity level of the message is logged. The print- options may
be used in any combination, and are always 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
If buffered has been turned on, the output to files is not
flushed after each log entry. By default all log messages are flushed.
There are four predefined channels that are used for named’s default
logging, as follows. If named is started with the -L option, then a fifth
channel, default_logfile, is added. How they are used is described in
The category Phrase.
channel default_syslog {
// send to syslog's daemon facility
syslog daemon;
// only send priority info and higher
severity info;
};
channel default_debug {
// write to named.run in the working directory
// Note: stderr is used instead of "named.run" if
// the server is started with the '-g' option.
file "named.run";
// log at the server's current debug level
severity dynamic;
};
channel default_stderr {
// writes to stderr
stderr;
// only send priority info and higher
severity info;
};
channel null {
// toss anything sent to this channel
null;
};
channel default_logfile {
// this channel is only present if named is
// started with the -L option, whose argument
// provides the file name
file "...";
// log at the server's current debug level
severity dynamic;
};
The default_debug channel has the special property that it only
produces output when the server’s debug level is non-zero. 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 -
and still running as root - is discarded. To capture this
output, run the server with the -L option to specify a
default logfile, or the -g option to log to standard error which can
be redirected to a file.
Once a channel is defined, it cannot be redefined. The built-in channels cannot be altered directly, but the default logging can be modified by pointing categories at defined channels.
4.2.10.2. The category Phrase¶
There are many categories, so desired logs can be sent anywhere
while unwanted logs are ignored. If
a list of channels is not specified for a category, log messages in that
category are sent to the default category instead. If no
default category is specified, the following “default default” is used:
category default { default_syslog; default_debug; };
If named is started with the -L option, the default category
is:
category default { default_logfile; default_debug; };
As an example, let’s say a user wants to log security events to a file, but also wants to keep the default logging behavior. They would 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; };
The 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.
clientProcessing of client requests.
cnameName servers that are skipped for being a CNAME rather than A/AAAA records.
configConfiguration file parsing and processing.
databaseMessages relating to the databases used internally by the name server to store zone and cache data.
defaultLogging options for those categories where no specific configuration has been defined.
delegation-onlyQueries that have been forced to NXDOMAIN as the result of a delegation-only zone or a
delegation-onlyin a forward, hint, or stub zone declaration.dispatchDispatching of incoming packets to the server modules where they are to be processed.
dnssecDNSSEC and TSIG protocol processing.
dnstapThe “dnstap” DNS traffic capture system.
edns-disabledLog queries that have been forced to use plain DNS due to timeouts. This is often due to the remote servers not being RFC 1034-compliant (not always returning FORMERR or similar to EDNS queries and other extensions to the DNS when they are not understood). In other words, this is targeted at servers that fail to respond to DNS queries that they don’t understand.
Note: the log message can also be due to packet loss. Before reporting servers for non-RFC 1034 compliance they should be re-tested to determine the nature of the non-compliance. This testing should prevent or reduce the number of false-positive reports.
Note: eventually
namedwill have to stop treating such timeouts as due to RFC 1034 non-compliance and start treating it as plain packet loss. Falsely classifying packet loss as due to RFC 1034 non-compliance impacts DNSSEC validation, which requires EDNS for the DNSSEC records to be returned.generalCatch-all for many things that still are not classified into categories.
lame-serversMisconfigurations in remote servers, discovered by BIND 9 when trying to query those servers during resolution.
networkNetwork operations.
notifyThe NOTIFY protocol.
nsidNSID options received from upstream servers.
queriesLocation where queries should be logged.
At startup, specifying the category
queriesalso enables query logging unless thequerylogoption has been specified.The query log entry first reports a client object identifier in @0x<hexadecimal-number> format. Next, it reports the client’s IP address and port number, and the query name, class, and type. Next, it reports whether the Recursion Desired flag was set (+ if set, - if not set), whether the query was signed (S), whether EDNS was in use along with the EDNS version number (E(#)), whether TCP was used (T), whether DO (DNSSEC Ok) was set (D), whether CD (Checking Disabled) was set (C), whether a valid DNS Server COOKIE was received (V), and whether a DNS COOKIE option without a valid Server COOKIE was present (K). After this, the destination address the query was sent to is reported. Finally, if any CLIENT-SUBNET option was present in the client query, it is included in square brackets in the format [ECS address/source/scope].
client 127.0.0.1#62536 (www.example.com):query: www.example.com IN AAAA +SEclient ::1#62537 (www.example.net):query: www.example.net IN AAAA -SEThe first part of this log message, showing the client address/port number and query name, is repeated in all subsequent log messages related to the same query.
query-errorsInformation about queries that resulted in some failure.
rate-limitStart, periodic, and final notices of the rate limiting of a stream of responses that are logged at
infoseverity in this category. These messages include a hash value of the domain name of the response and the name itself, except when there is insufficient memory to record the name for the final notice. The final notice is normally delayed until about one minute after rate limiting stops. A lack of memory can hurry the final notice, which is indicated by an initial asterisk (*). Various internal events are logged at debug level 1 and higher.Rate limiting of individual requests is logged in the
query-errorscategory.resolverDNS resolution, such as the recursive lookups performed on behalf of clients by a caching name server.
rpzInformation about errors in response policy zone files, rewritten responses, and, at the highest
debuglevels, mere rewriting attempts.rpz-passthruInformation about RPZ PASSTHRU policy activity. This category allows pre-approved policy activity to be logged into a dedicated channel.
securityApproval and denial of requests.
serve-staleIndication of whether a stale answer is used following a resolver failure.
spillQueries that have been terminated, either by dropping or responding with SERVFAIL, as a result of a fetchlimit quota being exceeded.
trust-anchor-telemetryTrust-anchor-telemetry requests received by
named.unmatchedMessages that
namedwas unable to determine the class of, or for which there was no matchingview. A one-line summary is also logged to theclientcategory. This category is best sent to a file or stderr; by default it is sent to thenullchannel.updateDynamic updates.
update-securityApproval and denial of update requests.
xfer-inZone transfers the server is receiving.
xfer-outZone transfers the server is sending.
zoneloadLoading of zones and creation of automatic empty zones.
4.2.10.3. The query-errors Category¶
The query-errors category is used to indicate why and how specific queries
resulted in responses which indicate an error. Normally, these messages are
logged at debug logging levels; note, however, that if query logging is
active, some are logged at info. The logging levels are described below:
At debug level 1 or higher - or at info when query logging is
active - 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 are particularly helpful in identifying
the cause of SERVFAIL for an authoritative server.
At debug level 2 or higher, detailed context information about recursive
resolutions that resulted in SERVFAIL is logged. The log message looks
like this:
fetch completed at resolver.c:2970 for www.example.com/A
in 10.000183: timed out/success [domain:example.com,
referral:2,restart:7,qrysent:8,timeout:5,lame:0,quota: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 10.000183 seconds, and the
final result that led to the SERVFAIL was determined at line 2970 of
source file resolver.c.
The next part shows the detected final result and the latest result of DNSSEC validation. The latter is always “success” when no validation attempt was made. In this example, this query probably resulted in SERVFAIL because all name servers are down or unreachable, leading to a timeout in 10 seconds. DNSSEC validation was probably not attempted.
The last part, enclosed in square brackets, shows statistics 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 list.
referralThe number of referrals the resolver received throughout the resolution process. In the above
example.comthere are two.restartThe number of cycles that the resolver tried remote servers at the
domainzone. In each cycle, the resolver sends one query (possibly resending it, depending on the response) to each known name server of thedomainzone.qrysentThe number of queries the resolver sent at the
domainzone.timeoutThe number of timeouts the resolver received since the last response.
lameThe number of lame servers the resolver detected at the
domainzone. A server is detected to be lame either by an invalid response or as a result of lookup in BIND 9’s address database (ADB), where lame servers are cached.quotaThe number of times the resolver was unable to send a query because it had exceeded the permissible fetch quota for a server.
neterrThe number of erroneous results that the resolver encountered in sending queries at the
domainzone. One common case is when the remote server is unreachable and the resolver receives an “ICMP unreachable” error message.badrespThe number of unexpected responses (other than
lame) to queries sent by the resolver at thedomainzone.adberrFailures in finding remote server addresses of the``domain`` zone in the ADB. One common case of this is that the remote server’s name does not have any address records.
findfailFailures to resolve remote server addresses. This is a total number of failures throughout the resolution process.
valfailFailures of DNSSEC validation. Validation failures are counted throughout the resolution process (not limited to the
domainzone), but should only happen indomain.
At debug level 3 or higher, the same messages as those at
debug level 1 are logged for errors other than
SERVFAIL. Note that negative responses such as NXDOMAIN are not errors, and are
not logged at this debug level.
At debug level 4 or higher, the detailed context information logged at
debug level 2 is logged for errors other than SERVFAIL and for negative
responses such as NXDOMAIN.
4.2.11. primaries Statement Grammar¶
primaries <string> [ port <integer> ] [ dscp
<integer> ] { ( <primaries> | <ipv4_address>
[ port <integer> ] | <ipv6_address> [ port
<integer> ] ) [ key <string> ] [ tls
<string> ]; ... };
4.2.12. primaries Statement Definition and Usage¶
primaries lists allow for a common set of primary servers to be easily
used by multiple stub and secondary zones in their primaries or
also-notify lists. (Note: primaries is a synonym for the original
keyword masters, which can still be used, but is no longer the
preferred terminology.)
4.2.13. options Statement Grammar¶
This is the grammar of the options statement in the named.conf
file:
options {
allow-new-zones <boolean>;
allow-notify { <address_match_element>; ... };
allow-query { <address_match_element>; ... };
allow-query-cache { <address_match_element>; ... };
allow-query-cache-on { <address_match_element>; ... };
allow-query-on { <address_match_element>; ... };
allow-recursion { <address_match_element>; ... };
allow-recursion-on { <address_match_element>; ... };
allow-transfer { <address_match_element>; ... };
allow-update { <address_match_element>; ... };
allow-update-forwarding { <address_match_element>; ... };
also-notify [ port <integer> ] [ dscp <integer> ] { ( <primaries> |
<ipv4_address> [ port <integer> ] | <ipv6_address> [ port
<integer> ] ) [ key <string> ] [ tls <string> ]; ... };
alt-transfer-source ( <ipv4_address> | * ) [ port ( <integer> | * )
] [ dscp <integer> ];
alt-transfer-source-v6 ( <ipv6_address> | * ) [ port ( <integer> |
* ) ] [ dscp <integer> ];
answer-cookie <boolean>;
attach-cache <string>;
auth-nxdomain <boolean>;
auto-dnssec ( allow | maintain | off );
automatic-interface-scan <boolean>;
avoid-v4-udp-ports { <portrange>; ... };
avoid-v6-udp-ports { <portrange>; ... };
bindkeys-file <quoted_string>;
blackhole { <address_match_element>; ... };
cache-file <quoted_string>;
catalog-zones { zone <string> [ default-masters [ port <integer> ]
[ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port
<integer> ] | <ipv6_address> [ port <integer> ] ) [ key
<string> ] [ tls <string> ]; ... } ] [ zone-directory
<quoted_string> ] [ in-memory <boolean> ] [ min-update-interval
<duration> ]; ... };
check-dup-records ( fail | warn | ignore );
check-integrity <boolean>;
check-mx ( fail | warn | ignore );
check-mx-cname ( fail | warn | ignore );
check-names ( primary | master |
secondary | slave | response ) (
fail | warn | ignore );
check-sibling <boolean>;
check-spf ( warn | ignore );
check-srv-cname ( fail | warn | ignore );
check-wildcard <boolean>;
clients-per-query <integer>;
cookie-algorithm ( aes | siphash24 );
cookie-secret <string>;
coresize ( default | unlimited | <sizeval> );
datasize ( default | unlimited | <sizeval> );
deny-answer-addresses { <address_match_element>; ... } [
except-from { <string>; ... } ];
deny-answer-aliases { <string>; ... } [ except-from { <string>; ...
} ];
dialup ( notify | notify-passive | passive | refresh | <boolean> );
directory <quoted_string>;
disable-algorithms <string> { <string>;
... };
disable-ds-digests <string> { <string>;
... };
disable-empty-zone <string>;
dns64 <netprefix> {
break-dnssec <boolean>;
clients { <address_match_element>; ... };
exclude { <address_match_element>; ... };
mapped { <address_match_element>; ... };
recursive-only <boolean>;
suffix <ipv6_address>;
};
dns64-contact <string>;
dns64-server <string>;
dnskey-sig-validity <integer>;
dnsrps-enable <boolean>;
dnsrps-options { <unspecified-text> };
dnssec-accept-expired <boolean>;
dnssec-dnskey-kskonly <boolean>;
dnssec-loadkeys-interval <integer>;
dnssec-must-be-secure <string> <boolean>;
dnssec-policy <string>;
dnssec-secure-to-insecure <boolean>;
dnssec-update-mode ( maintain | no-resign );
dnssec-validation ( yes | no | auto );
dnstap { ( all | auth | client | forwarder | resolver | update ) [
( query | response ) ]; ... };
dnstap-identity ( <quoted_string> | none | hostname );
dnstap-output ( file | unix ) <quoted_string> [ size ( unlimited |
<size> ) ] [ versions ( unlimited | <integer> ) ] [ suffix (
increment | timestamp ) ];
dnstap-version ( <quoted_string> | none );
dscp <integer>;
dual-stack-servers [ port <integer> ] { ( <quoted_string> [ port
<integer> ] [ dscp <integer> ] | <ipv4_address> [ port
<integer> ] [ dscp <integer> ] | <ipv6_address> [ port
<integer> ] [ dscp <integer> ] ); ... };
dump-file <quoted_string>;
edns-udp-size <integer>;
empty-contact <string>;
empty-server <string>;
empty-zones-enable <boolean>;
fetch-quota-params <integer> <fixedpoint> <fixedpoint> <fixedpoint>;
fetches-per-server <integer> [ ( drop | fail ) ];
fetches-per-zone <integer> [ ( drop | fail ) ];
files ( default | unlimited | <sizeval> );
flush-zones-on-shutdown <boolean>;
forward ( first | only );
forwarders [ port <integer> ] [ dscp <integer> ] { ( <ipv4_address>
| <ipv6_address> ) [ port <integer> ] [ dscp <integer> ]; ... };
fstrm-set-buffer-hint <integer>;
fstrm-set-flush-timeout <integer>;
fstrm-set-input-queue-size <integer>;
fstrm-set-output-notify-threshold <integer>;
fstrm-set-output-queue-model ( mpsc | spsc );
fstrm-set-output-queue-size <integer>;
fstrm-set-reopen-interval <duration>;
geoip-directory ( <quoted_string> | none );
glue-cache <boolean>; // deprecated
heartbeat-interval <integer>;
hostname ( <quoted_string> | none );
http-port <integer>;
https-port <integer>;
inline-signing <boolean>;
interface-interval <duration>;
ipv4only-contact <string>;
ipv4only-enable <boolean>;
ipv4only-server <string>;
ixfr-from-differences ( primary | master | secondary | slave |
<boolean> );
keep-response-order { <address_match_element>; ... };
key-directory <quoted_string>;
lame-ttl <duration>;
listen-on [ port <integer> ] [ dscp
<integer> ] [ tls <string> ] [ http
<string> ] {
<address_match_element>; ... };
listen-on-v6 [ port <integer> ] [ dscp
<integer> ] [ tls <string> ] [ http
<string> ] {
<address_match_element>; ... };
lmdb-mapsize <sizeval>;
lock-file ( <quoted_string> | none );
managed-keys-directory <quoted_string>;
masterfile-format ( map | raw | text );
masterfile-style ( full | relative );
match-mapped-addresses <boolean>;
max-cache-size ( default | unlimited | <sizeval> | <percentage> );
max-cache-ttl <duration>;
max-clients-per-query <integer>;
max-ixfr-ratio ( unlimited | <percentage> );
max-journal-size ( default | unlimited | <sizeval> );
max-ncache-ttl <duration>;
max-records <integer>;
max-recursion-depth <integer>;
max-recursion-queries <integer>;
max-refresh-time <integer>;
max-retry-time <integer>;
max-rsa-exponent-size <integer>;
max-stale-ttl <duration>;
max-transfer-idle-in <integer>;
max-transfer-idle-out <integer>;
max-transfer-time-in <integer>;
max-transfer-time-out <integer>;
max-udp-size <integer>;
max-zone-ttl ( unlimited | <duration> );
memstatistics <boolean>;
memstatistics-file <quoted_string>;
message-compression <boolean>;
min-cache-ttl <duration>;
min-ncache-ttl <duration>;
min-refresh-time <integer>;
min-retry-time <integer>;
minimal-any <boolean>;
minimal-responses ( no-auth | no-auth-recursive | <boolean> );
multi-master <boolean>;
new-zones-directory <quoted_string>;
no-case-compress { <address_match_element>; ... };
nocookie-udp-size <integer>;
notify ( explicit | master-only | primary-only | <boolean> );
notify-delay <integer>;
notify-rate <integer>;
notify-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [
dscp <integer> ];
notify-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * ) ]
[ dscp <integer> ];
notify-to-soa <boolean>;
nta-lifetime <duration>;
nta-recheck <duration>;
nxdomain-redirect <string>;
pid-file ( <quoted_string> | none );
port <integer>;
preferred-glue <string>;
prefetch <integer> [ <integer> ];
provide-ixfr <boolean>;
qname-minimization ( strict | relaxed | disabled | off );
query-source ( ( [ address ] ( <ipv4_address> | * ) [ port (
<integer> | * ) ] ) | ( [ [ address ] ( <ipv4_address> | * ) ]
port ( <integer> | * ) ) ) [ dscp <integer> ];
query-source-v6 ( ( [ address ] ( <ipv6_address> | * ) [ port (
<integer> | * ) ] ) | ( [ [ address ] ( <ipv6_address> | * ) ]
port ( <integer> | * ) ) ) [ dscp <integer> ];
querylog <boolean>;
random-device ( <quoted_string> | none );
rate-limit {
all-per-second <integer>;
errors-per-second <integer>;
exempt-clients { <address_match_element>; ... };
ipv4-prefix-length <integer>;
ipv6-prefix-length <integer>;
log-only <boolean>;
max-table-size <integer>;
min-table-size <integer>;
nodata-per-second <integer>;
nxdomains-per-second <integer>;
qps-scale <integer>;
referrals-per-second <integer>;
responses-per-second <integer>;
slip <integer>;
window <integer>;
};
recursing-file <quoted_string>;
recursion <boolean>;
recursive-clients <integer>;
request-expire <boolean>;
request-ixfr <boolean>;
request-nsid <boolean>;
require-server-cookie <boolean>;
reserved-sockets <integer>;
resolver-nonbackoff-tries <integer>;
resolver-query-timeout <integer>;
resolver-retry-interval <integer>;
response-padding { <address_match_element>; ... } block-size
<integer>;
response-policy { zone <string> [ add-soa <boolean> ] [ log
<boolean> ] [ max-policy-ttl <duration> ] [ min-update-interval
<duration> ] [ policy ( cname | disabled | drop | given | no-op
| nodata | nxdomain | passthru | tcp-only <quoted_string> ) ] [
recursive-only <boolean> ] [ nsip-enable <boolean> ] [
nsdname-enable <boolean> ]; ... } [ add-soa <boolean> ] [
break-dnssec <boolean> ] [ max-policy-ttl <duration> ] [
min-update-interval <duration> ] [ min-ns-dots <integer> ] [
nsip-wait-recurse <boolean> ] [ nsdname-wait-recurse <boolean>
] [ qname-wait-recurse <boolean> ] [ recursive-only <boolean> ]
[ nsip-enable <boolean> ] [ nsdname-enable <boolean> ] [
dnsrps-enable <boolean> ] [ dnsrps-options { <unspecified-text>
} ];
root-delegation-only [ exclude { <string>; ... } ];
root-key-sentinel <boolean>;
rrset-order { [ class <string> ] [ type <string> ] [ name
<quoted_string> ] <string> <string>; ... };
secroots-file <quoted_string>;
send-cookie <boolean>;
serial-query-rate <integer>;
serial-update-method ( date | increment | unixtime );
server-id ( <quoted_string> | none | hostname );
servfail-ttl <duration>;
session-keyalg <string>;
session-keyfile ( <quoted_string> | none );
session-keyname <string>;
sig-signing-nodes <integer>;
sig-signing-signatures <integer>;
sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ];
sortlist { <address_match_element>; ... };
stacksize ( default | unlimited | <sizeval> );
stale-answer-client-timeout ( disabled | off | <integer> );
stale-answer-enable <boolean>;
stale-answer-ttl <duration>;
stale-cache-enable <boolean>;
stale-refresh-time <duration>;
startup-notify-rate <integer>;
statistics-file <quoted_string>;
synth-from-dnssec <boolean>;
tcp-advertised-timeout <integer>;
tcp-clients <integer>;
tcp-idle-timeout <integer>;
tcp-initial-timeout <integer>;
tcp-keepalive-timeout <integer>;
tcp-listen-queue <integer>;
tkey-dhkey <quoted_string> <integer>;
tkey-domain <quoted_string>;
tkey-gssapi-credential <quoted_string>;
tkey-gssapi-keytab <quoted_string>;
tls-port <integer>;
transfer-format ( many-answers | one-answer );
transfer-message-size <integer>;
transfer-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [
dscp <integer> ];
transfer-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * )
] [ dscp <integer> ];
transfers-in <integer>;
transfers-out <integer>;
transfers-per-ns <integer>;
trust-anchor-telemetry <boolean>; // experimental
try-tcp-refresh <boolean>;
update-check-ksk <boolean>;
use-alt-transfer-source <boolean>;
use-v4-udp-ports { <portrange>; ... };
use-v6-udp-ports { <portrange>; ... };
v6-bias <integer>;
validate-except { <string>; ... };
version ( <quoted_string> | none );
zero-no-soa-ttl <boolean>;
zero-no-soa-ttl-cache <boolean>;
zone-statistics ( full | terse | none | <boolean> );
};
4.2.14. options Statement Definition and Usage¶
The options statement sets up global options to be used by BIND.
This statement may appear only once in a configuration file. If there is
no options statement, an options block with each option set to its
default is used.
attach-cacheThis option allows multiple views to share a single cache database. Each view has its own cache database by default, but if multiple views have the same operational policy for name resolution and caching, those views can share a single cache to save memory, and possibly improve resolution efficiency, by using this option.
The
attach-cacheoption may also be specified inviewstatements, in which case it overrides the globalattach-cacheoption.The
cache_namespecifies the cache to be shared. When thenamedserver configures views which are supposed to share a cache, it creates a cache with the specified name for the first view of these sharing views. The rest of the views simply refer to the already-created cache.One common configuration to share a cache is to allow all views to share a single cache. This can be done by specifying
attach-cacheas a global option with an arbitrary name.Another possible operation is to allow a subset of all views to share a cache while the others retain their own caches. For example, if there are three views A, B, and C, and only A and B should share a cache, specify the
attach-cacheoption as a view of A (or B)’s option, referring to the other view name:view "A" { // this view has its own cache ... }; view "B" { // this view refers to A's cache attach-cache "A"; }; view "C" { // this view has its own cache ... };
Views that share a cache must have the same policy on configurable parameters that may affect caching. The current implementation requires the following configurable options be consistent among these views:
check-names,dnssec-accept-expired,dnssec-validation,max-cache-ttl,max-ncache-ttl,max-stale-ttl,max-cache-size,min-cache-ttl,min-ncache-ttl, andzero-no-soa-ttl.Note that there may be other parameters that may cause confusion if they are inconsistent for different views that share a single cache. For example, if these views define different sets of forwarders that can return different answers for the same question, sharing the answer does not make sense or could even be harmful. It is the administrator’s responsibility to ensure that configuration differences in different views do not cause disruption with a shared cache.
directoryThis sets the working directory of the server. Any non-absolute pathnames in the configuration file are 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, and must be writable by the effective user ID of thenamedprocess.dnstapdnstapis a fast, flexible method for capturing and logging DNS traffic. Developed by Robert Edmonds at Farsight Security, Inc., and supported by multiple DNS implementations,dnstapuseslibfstrm(a lightweight high-speed framing library; see https://github.com/farsightsec/fstrm) to send event payloads which are encoded using Protocol Buffers (libprotobuf-c, a mechanism for serializing structured data developed by Google, Inc.; see https://developers.google.com/protocol-buffers/).To enable
dnstapat compile time, thefstrmandprotobuf-clibraries must be available, and BIND must be configured with--enable-dnstap.The
dnstapoption is a bracketed list of message types to be logged. These may be set differently for each view. Supported types areclient,auth,resolver,forwarder, andupdate. Specifying typeallcauses alldnstapmessages to be logged, regardless of type.Each type may take an additional argument to indicate whether to log
querymessages orresponsemessages; if not specified, both queries and responses are logged.Example: To log all authoritative queries and responses, recursive client responses, and upstream queries sent by the resolver, use:
dnstap { auth; client response; resolver query; };
Logged
dnstapmessages can be parsed using thednstap-readutility (see dnstap-read - print dnstap data in human-readable form for details).For more information on
dnstap, see http://dnstap.info.The fstrm library has a number of tunables that are exposed in
named.conf, and can be modified if necessary to improve performance or prevent loss of data. These are:fstrm-set-buffer-hint: The threshold number of bytes to accumulate in the output buffer before forcing a buffer flush. The minimum is 1024, the maximum is 65536, and the default is 8192.fstrm-set-flush-timeout: The number of seconds to allow unflushed data to remain in the output buffer. The minimum is 1 second, the maximum is 600 seconds (10 minutes), and the default is 1 second.fstrm-set-output-notify-threshold: The number of outstanding queue entries to allow on an input queue before waking the I/O thread. The minimum is 1 and the default is 32.fstrm-set-output-queue-model: The queuing semantics to use for queue objects. The default ismpsc(multiple producer, single consumer); the other option isspsc(single producer, single consumer).fstrm-set-input-queue-size: The number of queue entries to allocate for each input queue. This value must be a power of 2. The minimum is 2, the maximum is 16384, and the default is 512.fstrm-set-output-queue-size: The number of queue entries to allocate for each output queue. The minimum is 2, the maximum is system-dependent and based onIOV_MAX, and the default is 64.fstrm-set-reopen-interval: The number of seconds to wait between attempts to reopen a closed output stream. The minimum is 1 second, the maximum is 600 seconds (10 minutes), and the default is 5 seconds. For convenience, TTL-style time-unit suffixes may be used to specify the value.
Note that all of the above minimum, maximum, and default values are set by the
libfstrmlibrary, and may be subject to change in future versions of the library. See thelibfstrmdocumentation for more information.dnstap-outputThis configures the path to which the
dnstapframe stream is sent ifdnstapis enabled at compile time and active.The first argument is either
fileorunix, indicating whether the destination is a file or a Unix domain socket. The second argument is the path of the file or socket. (Note: when using a socket,dnstapmessages are only sent if another process such asfstrm_capture(provided withlibfstrm) is listening on the socket.)If the first argument is
file, then up to three additional options can be added:sizeindicates the size to which adnstaplog file can grow before being rolled to a new file;versionsspecifies the number of rolled log files to retain; andsuffixindicates whether to retain rolled log files with an incrementing counter as the suffix (increment) or with the current timestamp (timestamp). These are similar to thesize,versions, andsuffixoptions in aloggingchannel. The default is to allowdnstaplog files to grow to any size without rolling.dnstap-outputcan only be set globally inoptions. Currently, it can only be set once whilenamedis running; once set, it cannot be changed byrndc reloadorrndc reconfig.dnstap-identityThis specifies an
identitystring to send indnstapmessages. If set tohostname, which is the default, the server’s hostname is sent. If set tonone, no identity string is sent.dnstap-versionThis specifies a
versionstring to send indnstapmessages. The default is the version number of the BIND release. If set tonone, no version string is sent.geoip-directoryWhen
namedis compiled using the MaxMind GeoIP2 geolocation API, this specifies the directory containing GeoIP database files. By default, the option is set based on the prefix used to build thelibmaxminddbmodule; for example, if the library is installed in/usr/local/lib, then the defaultgeoip-directoryis/usr/local/share/GeoIP. On Windows, the default is thenamedworking directory. See acl Statement Definition and Usage for details aboutgeoipACLs.key-directoryThis is the directory where the public and private DNSSEC key files should be found when performing a dynamic update of secure zones, if different than the current working directory. (Note that this option has no effect on the paths for files containing non-DNSSEC keys such as
bind.keys,rndc.key, orsession.key.)lmdb-mapsizeWhen
namedis built with liblmdb, this option sets a maximum size for the memory map of the new-zone database (NZD) in LMDB database format. This database is used to store configuration information for zones added usingrndc addzone. Note that this is not the NZD database file size, but the largest size that the database may grow to.Because the database file is memory-mapped, its size is limited by the address space of the
namedprocess. The default of 32 megabytes was chosen to be usable with 32-bitnamedbuilds. The largest permitted value is 1 terabyte. Given typical zone configurations without elaborate ACLs, a 32 MB NZD file ought to be able to hold configurations of about 100,000 zones.managed-keys-directoryThis specifies the directory in which to store the files that track managed DNSSEC keys (i.e., those configured using the
initial-keyorinitial-dskeywords in atrust-anchorsstatement). By default, this is the working directory. The directory must be writable by the effective user ID of thenamedprocess.If
namedis not configured to use views, managed keys for the server are tracked in a single file calledmanaged-keys.bind. Otherwise, managed keys are tracked in separate files, one file per view; each file name is the view name (or, if it contains characters that are incompatible with use as a file name, the SHA256 hash of the view name), followed by the extension.mkeys.(Note: in earlier releases, file names for views always used the SHA256 hash of the view name. To ensure compatibility after upgrading, if a file using the old name format is found to exist, it is used instead of the new format.)
max-ixfr-ratioThis sets the size threshold (expressed as a percentage of the size of the full zone) beyond which
namedchooses to use an AXFR response rather than IXFR when answering zone transfer requests. See Incremental Zone Transfers (IXFR).The minimum value is
1%. The keywordunlimiteddisables ratio checking and allows IXFRs of any size. The default is100%.new-zones-directoryThis specifies the directory in which to store the configuration parameters for zones added via
rndc addzone. By default, this is the working directory. If set to a relative path, it is relative to the working directory. The directory must be writable by the effective user ID of thenamedprocess.qname-minimizationThis option controls QNAME minimization behavior in the BIND resolver. When set to
strict, BIND follows the QNAME minimization algorithm to the letter, as specified in RFC 7816. Setting this option torelaxedcauses BIND to fall back to normal (non-minimized) query mode when it receives either NXDOMAIN or other unexpected responses (e.g., SERVFAIL, improper zone cut, REFUSED) to a minimized query.disableddisables QNAME minimization completely. The current default isrelaxed, but it may be changed tostrictin a future release.tkey-gssapi-keytabThis is the KRB5 keytab file to use for GSS-TSIG updates. If this option is set and tkey-gssapi-credential is not set, updates are allowed with any key matching a principal in the specified keytab.
tkey-gssapi-credentialThis is the security credential with which the server should authenticate keys requested by the GSS-TSIG protocol. Currently only Kerberos 5 authentication is available; the credential is a Kerberos principal which the server can acquire through the default system key file, normally
/etc/krb5.keytab. The location of the keytab file can be overridden using thetkey-gssapi-keytaboption. Normally this principal is of the formDNS/server.domain. To use GSS-TSIG,tkey-domainmust also be set if a specific keytab is not set withtkey-gssapi-keytab.tkey-domainThis domain is appended to the names of all shared keys generated with
TKEY. When a client requests aTKEYexchange, it may or may not specify the desired name for the key. If present, the name of the shared key isclient-specified part+tkey-domain. Otherwise, the name of the shared key israndom hex digits+tkey-domain. In most cases, thedomainnameshould be the server’s domain name, or an otherwise nonexistent subdomain like_tkey.domainname. If using GSS-TSIG, this variable must be defined, unless a specific keytab is specified usingtkey-gssapi-keytab.tkey-dhkeyThis is 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, thekey_nameshould be the server’s host name.cache-fileThis is for testing only. Do not use.
dump-fileThis is the pathname of the file the server dumps the database to, when instructed to do so with
rndc dumpdb. If not specified, the default isnamed_dump.db.memstatistics-fileThis is the pathname of the file the server writes memory usage statistics to on exit. If not specified, the default is
named.memstats.lock-fileThis is the pathname of a file on which
namedattempts to acquire a file lock when starting for the first time; if unsuccessful, the server terminates, under the assumption that another server is already running. If not specified, the default isnone.Specifying
lock-file nonedisables the use of a lock file.lock-fileis ignored ifnamedwas run using the-Xoption, which overrides it. Changes tolock-fileare ignored ifnamedis being reloaded or reconfigured; it is only effective when the server is first started.pid-fileThis is the pathname of the file the server writes its process ID in. If not specified, the default is
/var/run/named/named.pid. The PID file is used by programs that send signals to the running name server. Specifyingpid-file nonedisables the use of a PID file; no file is written and any existing one is removed. Note thatnoneis a keyword, not a filename, and therefore is not enclosed in double quotes.recursing-fileThis is the pathname of the file where the server dumps the queries that are currently recursing, when instructed to do so with
rndc recursing. If not specified, the default isnamed.recursing.statistics-fileThis is the pathname of the file the server appends statistics to, when instructed to do so using
rndc stats. If not specified, the default isnamed.statsin the server’s current directory. The format of the file is described in The Statistics File.bindkeys-fileThis is the pathname of a file to override the built-in trusted keys provided by
named. See the discussion ofdnssec-validationfor details. If not specified, the default is/etc/bind.keys.secroots-fileThis is the pathname of the file the server dumps security roots to, when instructed to do so with
rndc secroots. If not specified, the default isnamed.secroots.session-keyfileThis is the pathname of the file into which to write a TSIG session key generated by
namedfor use bynsupdate -l. If not specified, the default is/var/run/named/session.key. (See Dynamic Update Policies, and in particular the discussion of theupdate-policystatement’slocaloption, for more information about this feature.)session-keynameThis is the key name to use for the TSIG session key. If not specified, the default is
local-ddns.session-keyalgThis is the algorithm to use for the TSIG session key. Valid values are hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384, hmac-sha512, and hmac-md5. If not specified, the default is hmac-sha256.
portThis is the UDP/TCP port number the server uses to receive and send DNS protocol traffic. The default is 53. This option is mainly intended for server testing; a server using a port other than 53 is not able to communicate with the global DNS.
tls-portThis is the TCP port number the server uses to receive and send DNS-over-TLS protocol traffic. The default is 853.
https-portThis is the TCP port number the server uses to receive and send DNS-over-HTTPS protocol traffic. The default is 443.
http-portThis is the TCP port number the server uses to receive and send unencrypted DNS traffic via HTTP (a configuration that may be useful when encryption is handled by third-party software or by a reverse proxy).
dscpThis is the global Differentiated Services Code Point (DSCP) value to classify outgoing DNS traffic, on operating systems that support DSCP. Valid values are 0 through 63. It is not configured by default.
random-deviceThis specifies a source of entropy to be used by the server; it is a device or file from which to read entropy. If it is a file, operations requiring entropy will fail when the file has been exhausted.
Entropy is needed for cryptographic operations such as TKEY transactions, dynamic update of signed zones, and generation of TSIG session keys. It is also used for seeding and stirring the pseudo-random number generator which is used for less critical functions requiring randomness, such as generation of DNS message transaction IDs.
If
random-deviceis not specified, or if it is set tonone, entropy is read from the random number generation function supplied by the cryptographic library with which BIND was linked (i.e. OpenSSL or a PKCS#11 provider).The
random-deviceoption takes effect during the initial configuration load at server startup time and is ignored on subsequent reloads.preferred-glueIf specified, the listed type (A or AAAA) is emitted before other glue in the additional section of a query response. The default is to prefer A records when responding to queries that arrived via IPv4 and AAAA when responding to queries that arrived via IPv6.
root-delegation-onlyThis turns 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 an 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 an 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 whether they are signed by a child zone, and the authority section is 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 that 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-algorithmsThis disables the specified DNSSEC algorithms at and below the specified name. Multiple
disable-algorithmsstatements are allowed. Only the best-matchdisable-algorithmsclause is used to determine the algorithms.If all supported algorithms are disabled, the zones covered by the
disable-algorithmssetting are treated as insecure.Configured trust anchors in
trust-anchors(ormanaged-keysortrusted-keys) that match a disabled algorithm are ignored and treated as if they were not configured.disable-ds-digestsThis disables the specified DS digest types at and below the specified name. Multiple
disable-ds-digestsstatements are allowed. Only the best-matchdisable-ds-digestsclause is used to determine the digest types.If all supported digest types are disabled, the zones covered by
disable-ds-digestsare treated as insecure.dnssec-must-be-secureThis specifies hierarchies which must be or may not be secure (signed and validated). If
yes, thennamedonly accepts answers if they are secure. Ifno, then normal DNSSEC validation applies, allowing insecure answers to be accepted. The specified domain must be defined as a trust anchor, for instance in atrust-anchorsstatement, ordnssec-validation automust be active.dns64This directive instructs
namedto return mapped IPv4 addresses to AAAA queries when there are no AAAA records. It is intended to be used in conjunction with a NAT64. Eachdns64defines one DNS64 prefix. Multiple DNS64 prefixes can be defined.Compatible IPv6 prefixes have lengths of 32, 40, 48, 56, 64, and 96, per RFC 6052. Bits 64..71 inclusive must be zero, with the most significant bit of the prefix in position 0.
In addition, a reverse IP6.ARPA zone is created for the prefix to provide a mapping from the IP6.ARPA names to the corresponding IN-ADDR.ARPA names using synthesized CNAMEs.
dns64-serveranddns64-contactcan be used to specify the name of the server and contact for the zones. These can be set at the view/options level but not on a per-prefix basis.dns64will also cause IPV4ONLY.ARPA to be created if not explicitly disabled usingipv4only-enable.Each
dns64supports an optionalclientsACL that determines which clients are affected by this directive. If not defined, it defaults toany;.Each
dns64supports an optionalmappedACL that selects which IPv4 addresses are to be mapped in the corresponding A RRset. If not defined, it defaults toany;.Normally, DNS64 does not apply to a domain name that owns one or more AAAA records; these records are simply returned. The optional
excludeACL allows specification of a list of IPv6 addresses that are ignored if they appear in a domain name’s AAAA records; DNS64 is applied to any A records the domain name owns. If not defined,excludedefaults to ::ffff:0.0.0.0/96.An optional
suffixcan also be defined to set the bits trailing the mapped IPv4 address bits. By default these bits are set to::. The bits matching the prefix and mapped IPv4 address must be zero.If
recursive-onlyis set toyes, the DNS64 synthesis only happens for recursive queries. The default isno.If
break-dnssecis set toyes, the DNS64 synthesis happens even if the result, if validated, would cause a DNSSEC validation failure. If this option is set tono(the default), the DO is set on the incoming query, and there are RRSIGs on the applicable records, then synthesis does not happen.acl rfc1918 { 10/8; 192.168/16; 172.16/12; }; dns64 64:FF9B::/96 { clients { any; }; mapped { !rfc1918; any; }; exclude { 64:FF9B::/96; ::ffff:0000:0000/96; }; suffix ::; };dnssec-loadkeys-intervalWhen a zone is configured with
auto-dnssec maintain;, its key repository must be checked periodically to see if any new keys have been added or any existing keys’ timing metadata has been updated (see dnssec-keygen: DNSSEC key generation tool and dnssec-settime: set the key timing metadata for a DNSSEC key). Thednssec-loadkeys-intervaloption sets the frequency of automatic repository checks, in minutes. The default is60(1 hour), the minimum is1(1 minute), and the maximum is1440(24 hours); any higher value is silently reduced.dnssec-policyThis specifies which key and signing policy (KASP) should be used for this zone. This is a string referring to a
dnssec-policystatement. There are two built-in policies:default, which uses the default policy, andnone, which means no DNSSEC policy and keeps the zone unsigned. The default isnone. See dnssec-policy Grammar for more details.dnssec-update-modeIf this option is set to its default value of
maintainin a zone of typeprimarywhich is DNSSEC-signed and configured to allow dynamic updates (see Dynamic Update Policies), and ifnamedhas access to the private signing key(s) for the zone, thennamedautomatically signs all new or changed records and maintains signatures for the zone by regenerating RRSIG records whenever they approach their expiration date.If the option is changed to
no-resign, thennamedsigns all new or changed records, but scheduled maintenance of signatures is disabled.With either of these settings,
namedrejects updates to a DNSSEC-signed zone when the signing keys are inactive or unavailable tonamed. (A planned third option,external, will disable all automatic signing and allow DNSSEC data to be submitted into a zone via dynamic update; this is not yet implemented.)nta-lifetimeThis specifies the default lifetime, in seconds, for negative trust anchors added via
rndc nta.A negative trust anchor selectively disables DNSSEC validation for zones that are known to be failing because of misconfiguration, rather than an attack. When data to be validated is at or below an active NTA (and above any other configured trust anchors),
namedaborts the DNSSEC validation process and treats the data as insecure rather than bogus. This continues until the NTA’s lifetime has elapsed. NTAs persist acrossnamedrestarts.For convenience, TTL-style time-unit suffixes can be used to specify the NTA lifetime in seconds, minutes, or hours. It also accepts ISO 8601 duration formats.
nta-lifetimedefaults to one hour; it cannot exceed one week.nta-recheckThis specifies how often to check whether negative trust anchors added via
rndc ntaare still necessary.A negative trust anchor is normally used when a domain has stopped validating due to operator error; it temporarily disables DNSSEC validation for that domain. In the interest of ensuring that DNSSEC validation is turned back on as soon as possible,
namedperiodically sends a query to the domain, ignoring negative trust anchors, to find out whether it can now be validated. If so, the negative trust anchor is allowed to expire early.Validity checks can be disabled for an individual NTA by using
rndc nta -f, or for all NTAs by settingnta-recheckto zero.For convenience, TTL-style time-unit suffixes can be used to specify the NTA recheck interval in seconds, minutes, or hours. It also accepts ISO 8601 duration formats.
The default is five minutes. It cannot be longer than
nta-lifetime, which cannot be longer than a week.max-zone-ttlThis specifies a maximum permissible TTL value in seconds. For convenience, TTL-style time-unit suffixes may be used to specify the maximum value. When loading a zone file using a
masterfile-formatoftextorraw, any record encountered with a TTL higher thanmax-zone-ttlcauses the zone to be rejected.This is useful in DNSSEC-signed zones because when rolling to a new DNSKEY, the old key needs to remain available until RRSIG records have expired from caches. The
max-zone-ttloption guarantees that the largest TTL in the zone is no higher than the set value.(Note: because
map-format files load directly into memory, this option cannot be used with them.)The default value is
unlimited. Amax-zone-ttlof zero is treated asunlimited.stale-answer-ttlThis specifies the TTL to be returned on stale answers. The default is 30 seconds. The minimum allowed is 1 second; a value of 0 is updated silently to 1 second.
For stale answers to be returned, they must be enabled, either in the configuration file using
stale-answer-enableor viarndc serve-stale on.serial-update-methodZones configured for dynamic DNS may use this option to set the update method to be used for the zone serial number in the SOA record.
With the default setting of
serial-update-method increment;, the SOA serial number is incremented by one each time the zone is updated.When set to
serial-update-method unixtime;, the SOA serial number is set to the number of seconds since the Unix epoch, unless the serial number is already greater than or equal to that value, in which case it is simply incremented by one.When set to
serial-update-method date;, the new SOA serial number is the current date in the form “YYYYMMDD”, followed by two zeroes, unless the existing serial number is already greater than or equal to that value, in which case it is incremented by one.zone-statisticsIf
full, the server collects statistical data on all zones, unless specifically turned off on a per-zone basis by specifyingzone-statistics terseorzone-statistics nonein thezonestatement. The statistical data includes, for example, DNSSEC signing operations and the number of authoritative answers per query type. The default isterse, providing minimal statistics on zones (including name and current serial number, but not query type counters).These statistics may be accessed via the
statistics-channelor usingrndc stats, which dumps them to the file listed in thestatistics-file. See also The Statistics File.For backward compatibility with earlier versions of BIND 9, the
zone-statisticsoption can also acceptyesorno;yeshas the same meaning asfull. As of BIND 9.10,nohas the same meaning asnone; previously, it was the same asterse.
4.2.14.1. Boolean Options¶
automatic-interface-scanIf
yesand supported by the operating system, this automatically rescans network interfaces when the interface addresses are added or removed. The default isyes. This configuration option does not affect the time-basedinterface-intervaloption; it is recommended to set the time-basedinterface-intervalto 0 when the operator confirms that automatic interface scanning is supported by the operating system.The
automatic-interface-scanimplementation uses routing sockets for the network interface discovery; therefore, the operating system must support the routing sockets for this feature to work.allow-new-zonesIf
yes, then zones can be added at runtime viarndc addzone. The default isno.Newly added zones’ configuration parameters are stored so that they can persist after the server is restarted. The configuration information is saved in a file called
viewname.nzf(or, ifnamedis compiled with liblmdb, in an LMDB database file calledviewname.nzd). “viewname” is the name of the view, unless the view name contains characters that are incompatible with use as a file name, in which case a cryptographic hash of the view name is used instead.Configurations for zones added at runtime are stored either in a new-zone file (NZF) or a new-zone database (NZD), depending on whether
namedwas linked with liblmdb at compile time. See rndc - name server control utility for further details aboutrndc addzone.auth-nxdomainIf
yes, then theAAbit is always set on NXDOMAIN responses, even if the server is not actually authoritative. The default isno.deallocate-on-exitThis option was used in BIND 8 to enable checking for memory leaks on exit. BIND 9 ignores the option and always performs the checks.
memstatisticsThis writes memory statistics to the file specified by
memstatistics-fileat exit. The default isnounless-m recordis specified on the command line, in which case it isyes.dialupIf
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. Although this setting has different effects according to zone type, it concentrates the zone maintenance so that everything happens quickly, once everyheartbeat-interval, ideally during a single call. It also suppresses some normal zone maintenance traffic. The default isno.If specified in the
viewandzonestatements, thedialupoption overrides the globaldialupoption.If the zone is a primary zone, the server sends out a NOTIFY request to all the secondaries (default). This should trigger the zone serial number check in the secondary (providing it supports NOTIFY), allowing the secondary to verify the zone while the connection is active. The set of servers to which NOTIFY is sent can be controlled by
notifyandalso-notify.If the zone is a secondary or stub zone, the server suppresses the regular “zone up to date” (refresh) queries and only performs them when the
heartbeat-intervalexpires, 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 theheartbeat-intervalexpires; andpassive, which disables normal refresh processing.dialup mode
normal refresh
heart-beat refresh
heart-beat notify
no(default)yes
no
no
yesno
yes
yes
notifyyes
no
yes
refreshno
yes
no
passiveno
no
no
notify-passiveno
no
yes
Note that normal NOTIFY processing is not affected by
dialup.flush-zones-on-shutdownWhen the name server exits upon receiving SIGTERM, flush or do not flush any pending zone writes. The default is
flush-zones-on-shutdown no.root-key-sentinelIf
yes, respond to root key sentinel probes as described in draft-ietf-dnsop-kskroll-sentinel-08. The default isyes.message-compressionIf
yes, DNS name compression is used in responses to regular queries (not including AXFR or IXFR, which always use compression). Setting this option tonoreduces CPU usage on servers and may improve throughput. However, it increases response size, which may cause more queries to be processed using TCP; a server with compression disabled is out of compliance with RFC 1123 Section 6.1.3.2. The default isyes.minimal-responsesThis option controls the addition of records to the authority and additional sections of responses. Such records may be included in responses to be helpful to clients; for example, NS or MX records may have associated address records included in the additional section, obviating the need for a separate address lookup. However, adding these records to responses is not mandatory and requires additional database lookups, causing extra latency when marshalling responses.
minimal-responsestakes one of four values:no: the server is as complete as possible when generating responses.yes: the server only adds records to the authority and additional sections when such records are required by the DNS protocol (for example, when returning delegations or negative responses). This provides the best server performance but may result in more client queries.no-auth: the server omits records from the authority section except when they are required, but it may still add records to the additional section.no-auth-recursive: the same asno-authwhen recursion is requested in the query (RD=1), or the same asnoif recursion is not requested.
no-authandno-auth-recursiveare useful when answering stub clients, which usually ignore the authority section.no-auth-recursiveis meant for use in mixed-mode servers that handle both authoritative and recursive queries.The default is
no-auth-recursive.glue-cacheWhen set to
yes, a cache is used to improve query performance when adding address-type (A and AAAA) glue records to the additional section of DNS response messages that delegate to a child zone.The glue cache uses memory proportional to the number of delegations in the zone. The default setting is
yes, which improves performance at the cost of increased memory usage for the zone. To avoid this, set it tono.Note
This option is deprecated and its use is discouraged. The glue cache will be permanently enabled in a future release.
minimal-anyIf set to
yes, the server replies with only one of the RRsets for the query name, and its covering RRSIGs if any, when generating a positive response to a query of type ANY over UDP, instead of replying with all known RRsets for the name. Similarly, a query for type RRSIG is answered with the RRSIG records covering only one type. This can reduce the impact of some kinds of attack traffic, without harming legitimate clients. (Note, however, that the RRset returned is the first one found in the database; it is not necessarily the smallest available RRset.) Additionally,minimal-responsesis turned on for these queries, so no unnecessary records are added to the authority or additional sections. The default isno.notifyIf set to
yes(the default), DNS NOTIFY messages are sent when a zone the server is authoritative for changes; see Notify. The messages are sent to the servers listed in the zone’s NS records (except the primary server identified in the SOA MNAME field), and to any servers listed in thealso-notifyoption.If set to
primary-only(or the older keywordmaster-only), notifies are only sent for primary zones. If set toexplicit, notifies are sent only to servers explicitly listed usingalso-notify. If set tono, no notifies are sent.The
notifyoption may also be specified in thezonestatement, in which case it overrides theoptions notifystatement. It would only be necessary to turn off this option if it caused secondary zones to crash.notify-to-soaIf
yes, do not check the name servers in the NS RRset against the SOA MNAME. Normally a NOTIFY message is not sent to the SOA MNAME (SOA ORIGIN), as it is supposed to contain the name of the ultimate primary server. Sometimes, however, a secondary server is listed as the SOA MNAME in hidden primary configurations; in that case, the ultimate primary should be set to still send NOTIFY messages to all the name servers listed in the NS RRset.recursionIf
yes, and a DNS query requests recursion, then the server attempts to do all the work required to answer the query. If recursion is off and the server does not already know the answer, it returns a referral response. The default isyes. Note that settingrecursion nodoes 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 of the server’s internal operation, such as NOTIFY address lookups.request-nsidIf
yes, then an empty EDNS(0) NSID (Name Server Identifier) option is sent with all queries to authoritative name servers during iterative resolution. If the authoritative server returns an NSID option in its response, then its contents are logged in thensidcategory at levelinfo. The default isno.require-server-cookieIf
yes, require a valid server cookie before sending a full response to a UDP request from a cookie-aware client. BADCOOKIE is sent if there is a bad or nonexistent server cookie.The default is
no.Users wishing to test that DNS COOKIE clients correctly handle BADCOOKIE, or who are getting a lot of forged DNS requests with DNS COOKIES present, should set this to
yes. Setting this toyesresults in a reduced amplification effect in a reflection attack, as the BADCOOKIE response is smaller than a full response, while also requiring a legitimate client to follow up with a second query with the new, valid, cookie.answer-cookieWhen set to the default value of
yes, COOKIE EDNS options are sent when applicable in replies to client queries. If set tono, COOKIE EDNS options are not sent in replies. This can only be set at the global options level, not per-view.answer-cookie nois intended as a temporary measure, for use whennamedshares an IP address with other servers that do not yet support DNS COOKIE. A mismatch between servers on the same address is not expected to cause operational problems, but the option to disable COOKIE responses so that all servers have the same behavior is provided out of an abundance of caution. DNS COOKIE is an important security mechanism, and should not be disabled unless absolutely necessary.send-cookieIf
yes, then a COOKIE EDNS option is sent along with the query. If the resolver has previously communicated with the server, the COOKIE returned in the previous transaction is sent. This is used by the server to determine whether the resolver has talked to it before. A resolver sending the correct COOKIE is assumed not to be an off-path attacker sending a spoofed-source query; the query is therefore unlikely to be part of a reflection/amplification attack, so resolvers sending a correct COOKIE option are not subject to response rate limiting (RRL). Resolvers which do not send a correct COOKIE option may be limited to receiving smaller responses via thenocookie-udp-sizeoption.The default is
yes.stale-answer-enableIf
yes, enable the returning of “stale” cached answers when the name servers for a zone are not answering and thestale-cache-enableoption is also enabled. The default is not to return stale answers.Stale answers can also be enabled or disabled at runtime via
rndc serve-stale onorrndc serve-stale off; these override the configured setting.rndc serve-stale resetrestores the setting to the one specified innamed.conf. Note that if stale answers have been disabled byrndc, they cannot be re-enabled by reloading or reconfiguringnamed; they must be re-enabled withrndc serve-stale on, or the server must be restarted.Information about stale answers is logged under the
serve-stalelog category.stale-answer-client-timeoutThis option defines the amount of time (in milliseconds) that
namedwaits before attempting to answer the query with a stale RRset from cache. If a stale answer is found,namedcontinues the ongoing fetches, attempting to refresh the RRset in cache until theresolver-query-timeoutinterval is reached.This option is off by default, which is equivalent to setting it to
offordisabled. It also has no effect ifstale-answer-enableis disabled.The maximum value for this option is
resolver-query-timeoutminus one second. The minimum value,0, causes a cached RRset to be immediately returned if it is available while still attempting to refresh the data in cache. RFC 8767 recommends a value of1800(milliseconds).stale-cache-enableIf
yes, enable the retaining of “stale” cached answers. Defaultno.stale-refresh-timeIf the name servers for a given zone are not answering, this sets the time window for which
namedwill promptly return “stale” cached answers for that RRSet being requested before a new attempt in contacting the servers is made. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.The default
stale-refresh-timeis 30 seconds, as RFC 8767 recommends that attempts to refresh to be done no more frequently than every 30 seconds. A value of zero disables the feature, meaning that normal resolution will take place first, if that fails only thennamedwill return “stale” cached answers.nocookie-udp-sizeThis sets the maximum size of UDP responses that are sent to queries without a valid server COOKIE. A value below 128 is silently raised to 128. The default value is 4096, but the
max-udp-sizeoption may further limit the response size as the default formax-udp-sizeis 1232.cookie-algorithmThis sets the algorithm to be used when generating the server cookie; the options are “aes”, “sha1”, or “sha256”. The default is “aes” if supported by the cryptographic library; otherwise, “sha256”.
cookie-secretIf set, this is a shared secret used for generating and verifying EDNS COOKIE options within an anycast cluster. If not set, the system generates a random secret at startup. The shared secret is encoded as a hex string and needs to be 128 bits for AES128, 160 bits for SHA1, and 256 bits for SHA256.
If there are multiple secrets specified, the first one listed in
named.confis used to generate new server cookies. The others are only used to verify returned cookies.response-paddingThe EDNS Padding option is intended to improve confidentiality when DNS queries are sent over an encrypted channel, by reducing the variability in packet sizes. If a query:
contains an EDNS Padding option,
includes a valid server cookie or uses TCP,
is not signed using TSIG or SIG(0), and
is from a client whose address matches the specified ACL,
then the response is padded with an EDNS Padding option to a multiple of
block-sizebytes. If these conditions are not met, the response is not padded.If
block-sizeis 0 or the ACL isnone;, this feature is disabled and no padding occurs; this is the default. Ifblock-sizeis greater than 512, a warning is logged and the value is truncated to 512. Block sizes are ordinarily expected to be powers of two (for instance, 128), but this is not mandatory.trust-anchor-telemetryThis causes
namedto send specially formed queries once per day to domains for which trust anchors have been configured via, e.g.,trust-anchorsordnssec-validation auto.The query name used for these queries has the form
_ta-xxxx(-xxxx)(...).<domain>, where each “xxxx” is a group of four hexadecimal digits representing the key ID of a trusted DNSSEC key. The key IDs for each domain are sorted smallest to largest prior to encoding. The query type is NULL.By monitoring these queries, zone operators are able to see which resolvers have been updated to trust a new key; this may help them decide when it is safe to remove an old one.
The default is
yes.provide-ixfrSee the description of
provide-ixfrin server Statement Definition and Usage.request-ixfrSee the description of
request-ixfrin server Statement Definition and Usage.request-expireSee the description of
request-expirein server Statement Definition and Usage.match-mapped-addressesIf
yes, then an IPv4-mapped IPv6 address matches any address-match list entries that match the corresponding IPv4 address.This option was introduced to work around a kernel quirk in some operating systems that causes IPv4 TCP connections, such as zone transfers, to be accepted on an IPv6 socket using mapped addresses. This caused address-match lists designed for IPv4 to fail to match. However,
namednow solves this problem internally. The use of this option is discouraged.ixfr-from-differencesWhen
yesand the server loads a new version of a primary zone from its zone file or receives a new version of a secondary file via zone transfer, it compares the new version to the previous one and calculates a set of differences. The differences are then logged in the zone’s journal file so that the changes can be transmitted to downstream secondaries 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 primary server. In particular, if the new version of a zone is completely different from the previous one, the set of differences is of a size comparable to the combined size of the old and new zone versions, and the server needs to temporarily allocate memory to hold this complete difference set.
ixfr-from-differencesalso acceptsprimaryandsecondaryat the view and options levels, which causesixfr-from-differencesto be enabled for all primary or secondary zones, respectively. It is off for all zones by default.Note: if inline signing is enabled for a zone, the user-provided
ixfr-from-differencessetting is ignored for that zone.multi-masterThis should be set when there are multiple primary servers for a zone and the addresses refer to different machines. If
yes,nameddoes not log when the serial number on the primary is less than whatnamedcurrently has. The default isno.auto-dnssecZones configured for dynamic DNS may use this option to allow varying levels of automatic DNSSEC key management. There are three possible settings:
auto-dnssec allow;permits keys to be updated and the zone fully re-signed whenever the user issues the commandrndc sign zonename.auto-dnssec maintain;includes the above, but also automatically adjusts the zone’s DNSSEC keys on a schedule, according to the keys’ timing metadata (see dnssec-keygen: DNSSEC key generation tool and dnssec-settime: set the key timing metadata for a DNSSEC key). The commandrndc sign zonenamecausesnamedto load keys from the key repository and sign the zone with all keys that are active.rndc loadkeys zonenamecausesnamedto load keys from the key repository and schedule key maintenance events to occur in the future, but it does not sign the full zone immediately. Note: once keys have been loaded for a zone the first time, the repository is searched for changes periodically, regardless of whetherrndc loadkeysis used. The recheck interval is defined bydnssec-loadkeys-interval.The default setting is
auto-dnssec off.
dnssec-validationThis option enables DNSSEC validation in
named.If set to
auto, DNSSEC validation is enabled and a default trust anchor for the DNS root zone is used.If set to
yes, DNSSEC validation is enabled, but a trust anchor must be manually configured using atrust-anchorsstatement (or themanaged-keysortrusted-keysstatements, both deprecated). If there is no configured trust anchor, validation does not take place.If set to
no, DNSSEC validation is disabled.The default is
auto, unless BIND is built withconfigure --disable-auto-validation, in which case the default isyes.The default root trust anchor is stored in the file
bind.keys.namedloads that key at startup ifdnssec-validationis set toauto. A copy of the file is installed along with BIND 9, and is current as of the release date. If the root key expires, a new copy ofbind.keyscan be downloaded from https://www.isc.org/bind-keys.(To prevent problems if
bind.keysis not found, the current trust anchor is also compiled innamed. Relying on this is not recommended, however, as it requiresnamedto be recompiled with a new key when the root key expires.)Note
namedloads only the root key frombind.keys. The file cannot be used to store keys for other zones. The root key inbind.keysis ignored ifdnssec-validation autois not in use.Whenever the resolver sends out queries to an EDNS-compliant server, it always sets the DO bit indicating it can support DNSSEC responses, even if
dnssec-validationis off.validate-exceptThis specifies a list of domain names at and beneath which DNSSEC validation should not be performed, regardless of the presence of a trust anchor at or above those names. This may be used, for example, when configuring a top-level domain intended only for local use, so that the lack of a secure delegation for that domain in the root zone does not cause validation failures. (This is similar to setting a negative trust anchor except that it is a permanent configuration, whereas negative trust anchors expire and are removed after a set period of time.)
dnssec-accept-expiredThis accepts expired signatures when verifying DNSSEC signatures. The default is
no. Setting this option toyesleavesnamedvulnerable to replay attacks.querylogQuery logging provides a complete log of all incoming queries and all query errors. This provides more insight into the server’s activity, but with a cost to performance which may be significant on heavily loaded servers.
The
querylogoption specifies whether query logging should be active whennamedfirst starts. Ifquerylogis not specified, then query logging is determined by the presence of the logging categoryqueries. Query logging can also be activated at runtime using the commandrndc querylog on, or deactivated withrndc querylog off.check-namesThis option is used to restrict the character set and syntax of certain domain names in primary files and/or DNS responses received from the network. The default varies according to usage area. For
primaryzones the default isfail. Forsecondaryzones the default iswarn. For answers received from the network (response), the default isignore.The rules for legal hostnames and mail domains are derived from RFC 952 and RFC 821 as modified by RFC 1123.
check-namesapplies 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 further applies to the RDATA of PTR records where the owner name indicates that it is a reverse lookup of a hostname (the owner name ends in IN-ADDR.ARPA, IP6.ARPA, or IP6.INT).check-dup-recordsThis checks primary zones for records that are treated as different by DNSSEC but are semantically equal in plain DNS. The default is to
warn. Other possible values arefailandignore.check-mxThis checks whether the MX record appears to refer to an IP address. The default is to
warn. Other possible values arefailandignore.check-wildcardThis option is used to check for non-terminal wildcards. The use of non-terminal wildcards is almost always as a result of a lack of understanding of the wildcard matching algorithm (RFC 1034). This option affects primary zones. The default (
yes) is to check for non-terminal wildcards and issue a warning.check-integrityThis performs post-load zone integrity checks on primary zones. It 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, usenamed-checkzone). The default isyes.The use of the SPF record to publish Sender Policy Framework is deprecated, as the migration from using TXT records to SPF records was abandoned. Enabling this option also checks that a TXT Sender Policy Framework record exists (starts with “v=spf1”) if there is an SPF record. Warnings are emitted if the TXT record does not exist; they can be suppressed with
check-spf.check-mx-cnameIf
check-integrityis set, then fail, warn, or ignore MX records that refer to CNAMES. The default is towarn.check-srv-cnameIf
check-integrityis set, then fail, warn, or ignore SRV records that refer to CNAMES. The default is towarn.check-siblingWhen performing integrity checks, also check that sibling glue exists. The default is
yes.check-spfIf
check-integrityis set, check that there is a TXT Sender Policy Framework record present (starts with “v=spf1”) if there is an SPF record present. The default iswarn.zero-no-soa-ttlIf
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 isyes.zero-no-soa-ttl-cacheIf
yes, when caching a negative response to an SOA query set the TTL to zero. The default isno.update-check-kskWhen set to the default value of
yes, check the KSK bit in each key to determine how the key should be used when generating RRSIGs for a secure zone.Ordinarily, zone-signing keys (that is, keys without the KSK bit set) are used to sign the entire zone, while key-signing keys (keys with the KSK bit set) are only used to sign the DNSKEY RRset at the zone apex. However, if this option is set to
no, then the KSK bit is ignored; KSKs are treated as if they were ZSKs and are used to sign the entire zone. This is similar to thednssec-signzone -zcommand-line option.When this option is set to
yes, there must be at least two active keys for every algorithm represented in the DNSKEY RRset: at least one KSK and one ZSK per algorithm. If there is any algorithm for which this requirement is not met, this option is ignored for that algorithm.dnssec-dnskey-kskonlyWhen this option and
update-check-kskare both set toyes, only key-signing keys (that is, keys with the KSK bit set) are used to sign the DNSKEY, CDNSKEY, and CDS RRsets at the zone apex. Zone-signing keys (keys without the KSK bit set) are used to sign the remainder of the zone, but not the DNSKEY RRset. This is similar to thednssec-signzone -xcommand-line option.The default is
no. Ifupdate-check-kskis set tono, this option is ignored.try-tcp-refreshIf
yes, try to refresh the zone using TCP if UDP queries fail. The default isyes.dnssec-secure-to-insecureThis allows a dynamic zone to transition from secure to insecure (i.e., signed to unsigned) by deleting all of the DNSKEY records. The default is
no. If set toyes, and if the DNSKEY RRset at the zone apex is deleted, all RRSIG and NSEC records are removed from the zone as well.If the zone uses NSEC3, it is also necessary to delete the NSEC3PARAM RRset from the zone apex; this causes the removal of all corresponding NSEC3 records. (It is expected that this requirement will be eliminated in a future release.)
Note that if a zone has been configured with
auto-dnssec maintainand the private keys remain accessible in the key repository, the zone will be automatically signed again the next timenamedis started.synth-from-dnssecThis option synthesizes answers from cached NSEC, NSEC3, and other RRsets that have been proved to be correct using DNSSEC. The default is
no, but it will becomeyesagain in future releases.Note
DNSSEC validation must be enabled for this option to be effective. This initial implementation only covers synthesis of answers from NSEC records; synthesis from NSEC3 is planned for the future. This will also be controlled by
synth-from-dnssec.
4.2.14.2. Forwarding¶
The forwarding facility can be used to create a large site-wide cache on a few servers, reducing traffic over links to external name servers. It can also be used to allow queries by servers that do not have direct access to the Internet, but wish to look up exterior names anyway. Forwarding occurs only on those queries for which the server is not authoritative and does not have the answer in its cache.
forwardThis option is only meaningful if the forwarders list is not empty. A value of
firstis the default and causes the server to query the forwarders first; if that does not answer the question, the server then looks for the answer itself. Ifonlyis specified, the server only queries the forwarders.forwardersThis specifies a list of IP addresses to which queries are forwarded. The default is the empty list (no forwarding). Each address in the list can be associated with an optional port number and/or DSCP value, and a default port number and DSCP value can be set for the entire list.
Forwarding can also be configured on a per-domain basis, allowing for
the global forwarding options to be overridden in a variety of ways.
Particular domains can be set to use different forwarders, or have a
different forward only/first behavior, or not forward at all; see
zone Statement Grammar.
4.2.14.3. Dual-stack Servers¶
Dual-stack servers are used as servers of last resort, to work around problems in reachability due to the lack of support for either IPv4 or IPv6 on the host machine.
dual-stack-serversThis 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, the
dual-stack-serversparameter has no effect unless access to a transport has been disabled on the command line (e.g.,named -4).
4.2.14.4. Access Control¶
Access to the server can be restricted based on the IP address of the requesting system. See Address Match Lists for details on how to specify IP address lists.
allow-notifyThis ACL specifies which hosts may send NOTIFY messages to inform this server of changes to zones for which it is acting as a secondary server. This is only applicable for secondary zones (i.e., type
secondaryorslave).If this option is set in
vieworoptions, it is globally applied to all secondary zones. If set in thezonestatement, the global value is overridden.If not specified, the default is to process NOTIFY messages only from the configured
primariesfor the zone.allow-notifycan be used to expand the list of permitted hosts, not to reduce it.allow-queryThis specifies which hosts are allowed to ask ordinary DNS questions.
allow-querymay also be specified in thezonestatement, in which case it overrides theoptions allow-querystatement. If not specified, the default is to allow queries from all hosts.Note
allow-query-cacheis used to specify access to the cache.allow-query-onThis specifies which local addresses can accept ordinary DNS questions. This makes it possible, for instance, to allow queries on internal-facing interfaces but disallow them on external-facing ones, without necessarily knowing the internal network’s addresses.
Note that
allow-query-onis only checked for queries that are permitted byallow-query. A query must be allowed by both ACLs, or it is refused.allow-query-onmay also be specified in thezonestatement, in which case it overrides theoptions allow-query-onstatement.If not specified, the default is to allow queries on all addresses.
Note
allow-query-cacheis used to specify access to the cache.allow-query-cacheThis specifies which hosts are allowed to get answers from the cache. If
allow-recursionis not set, BIND checks to see if the following parameters are set, in order:allow-query-cacheandallow-query(unlessrecursion no;is set). If neither of those parameters is set, the default (localnets; localhost;) is used.allow-query-cache-onThis specifies which local addresses can send answers from the cache. If
allow-query-cache-onis not set, thenallow-recursion-onis used if set. Otherwise, the default is to allow cache responses to be sent from any address. Note: bothallow-query-cacheandallow-query-cache-onmust be satisfied before a cache response can be sent; a client that is blocked by one cannot be allowed by the other.allow-recursionThis specifies which hosts are allowed to make recursive queries through this server. BIND checks to see if the following parameters are set, in order:
allow-query-cacheandallow-query. If neither of those parameters is set, the default (localnets; localhost;) is used.allow-recursion-onThis specifies which local addresses can accept recursive queries. If
allow-recursion-onis not set, thenallow-query-cache-onis used if set; otherwise, the default is to allow recursive queries on all addresses. Any client permitted to send recursive queries can send them to any address on whichnamedis listening. Note: bothallow-recursionandallow-recursion-onmust be satisfied before recursion is allowed; a client that is blocked by one cannot be allowed by the other.allow-updateWhen set in the
zonestatement for a primary zone, this specifies which hosts are allowed to submit Dynamic DNS updates to that zone. The default is to deny updates from all hosts.Note that allowing updates based on the requestor’s IP address is insecure; see Dynamic Update Security for details.
In general, this option should only be set at the
zonelevel. While a default value can be set at theoptionsorviewlevel and inherited by zones, this could lead to some zones unintentionally allowing updates.allow-update-forwardingWhen set in the
zonestatement for a secondary zone, this specifies which hosts are allowed to submit Dynamic DNS updates and have them be forwarded to the primary. The default is{ none; }, which means that no update forwarding is performed.To enable update forwarding, specify
allow-update-forwarding { any; };in thezonestatement. Specifying values other than{ none; }or{ any; }is usually counterproductive; the responsibility for update access control should rest with the primary server, not the secondary.Note that enabling the update forwarding feature on a secondary server may expose primary servers to attacks if they rely on insecure IP-address-based access control; see Dynamic Update Security for more details.
In general this option should only be set at the
zonelevel. While a default value can be set at theoptionsorviewlevel and inherited by zones, this can lead to some zones unintentionally forwarding updates.
allow-transferThis specifies which hosts are allowed to receive zone transfers from the server.
allow-transfermay also be specified in thezonestatement, in which case it overrides theallow-transferstatement set inoptionsorview. If not specified, the default is to allow transfers to all hosts.blackholeThis specifies a list of addresses which the server does not accept queries from or use to resolve a query. Queries from these addresses are not responded to. The default is
none.keep-response-orderThis specifies a list of addresses to which the server sends responses to TCP queries, in the same order in which they were received. This disables the processing of TCP queries in parallel. The default is
none.no-case-compressThis specifies a list of addresses which require responses to use case-insensitive compression. This ACL can be used when
namedneeds to work with clients that do not comply with the requirement in RFC 1034 to use case-insensitive name comparisons when checking for matching domain names.If left undefined, the ACL defaults to
none: case-insensitive compression is used for all clients. If the ACL is defined and matches a client, case is ignored when compressing domain names in DNS responses sent to that client.This can result in slightly smaller responses; if a response contains the names “example.com” and “example.COM”, case-insensitive compression treats the second one as a duplicate. It also ensures that the case of the query name exactly matches the case of the owner names of returned records, rather than matches the case of the records entered in the zone file. This allows responses to exactly match the query, which is required by some clients due to incorrect use of case-sensitive comparisons.
Case-insensitive compression is always used in AXFR and IXFR responses, regardless of whether the client matches this ACL.
There are circumstances in which
nameddoes not preserve the case of owner names of records: if a zone file defines records of different types with the same name, but the capitalization of the name is different (e.g., “www.example.com/A” and “WWW.EXAMPLE.COM/AAAA”), then all responses for that name use the first version of the name that was used in the zone file. This limitation may be addressed in a future release. However, domain names specified in the rdata of resource records (i.e., records of type NS, MX, CNAME, etc.) always have their case preserved unless the client matches this ACL.resolver-query-timeoutThis is the amount of time in milliseconds that the resolver spends attempting to resolve a recursive query before failing. The default and minimum is
10000and the maximum is30000. Setting it to0results in the default being used.This value was originally specified in seconds. Values less than or equal to 300 are treated as seconds and converted to milliseconds before applying the above limits.
4.2.14.5. Interfaces¶
The interfaces, ports, and protocols that the server can use to answer
queries may be specified using the listen-on and listen-on-v6 options.
listen-on and listen-on-v6 statements can each take an optional
port, TLS configuration identifier, and/or HTTP configuration identifier,
in addition to an address_match_list.
The address_match_list in listen-on specifies the IPv4 addresses
on which the server will listen. (IPv6 addresses are ignored, with a
logged warning.) The server listens on all interfaces allowed by the
address match list. If no listen-on is specified, the default is
to listen for standard DNS queries on port 53 of all IPv4 interfaces.
listen-on-v6 takes an address_match_list of IPv6 addresses.
The server listens on all interfaces allowed by the address match list.
If no listen-on-v6 is specified, the default is to listen for standard
DNS queries on port 53 of all IPv6 interfaces.
If a TLS configuration is specified, named will listen for DNS-over-TLS
(DoT) connections, using the key and certificate specified in the
referenced tls statement. If the name ephemeral is used,
an ephemeral key and certificate created for the currently running
named process will be used.
If an HTTP configuration is specified, named will listen for
DNS-over-HTTPS (DoH) connections using the HTTP endpoint specified in the
referenced http statement. If the name default is used, then
named will listen for connections at the default endpoint,
/dns-query.
Use of an http specification requires tls to be specified
as well. If an unencrypted connection is desired (for example,
on load-sharing servers behind a reverse proxy), tls none may be used.
If a port number is not specified, the default is 53 for standard DNS, 853
for DNS over TLS, 443 for DNS over HTTPS, and 80 for DNS over unenecrypted
HTTP. These defaults may be overridden using the port, tls-port,
https-port and http-port options.
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; };
listen-on port 8853 tls ephemeral { 4.3.2.1; };
listen-on port 8453 tls ephemeral http myserver { 8.7.6.5; };
The first two lines instruct the name server to listen for standard DNS
queries on port 53 of 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. The third line instructs the
server to listen for DNS-over-TLS connections on port 8853 of the IP
address 4.3.2.1 using the ephemeral key and certifcate. The fourth line
enables DNS-over-HTTPS connections on port 8453 of address 8.7.6.5, using
the ephemeral key and certificate, and the HTTP endpoint or endpoints
configured in an http statement with the name myserver.
Multiple listen-on-v6 options can be used. For example:
listen-on-v6 { any; };
listen-on-v6 port 1234 { !2001:db8::/32; any; };
listen-on port 8853 tls example-tls { 2001:db8::100; };
listen-on port 8453 tls example-tls http default { 2001:db8::100; };
listen-on port 8000 tls none http myserver { 2001:db8::100; };
The first two lines instruct the name server to listen for standard DNS
queries on port 53 of any IPv6 addresses, and on port 1234 of IPv6
addresses that are not in the prefix 2001:db8::/32. The third line
instructs the server to listen for for DNS-over-TLS connections on port
8853 of the address 2001:db8::100, using a TLS key and certificate specified
in the a tls statement with the name example-tls. The fourth
instructs the server to listen for DNS-over-HTTPS connections, again using
example-tls, on the default HTTP endpoint. The fifth line, in which
the tls parameter is set to none, instructs the server to listen
for unencrypted DNS queries over HTTP at the endpoint specified in
myserver..
To instruct the server not to listen on any IPv6 addresses, use:
listen-on-v6 { none; };
4.2.14.6. Query Address¶
If the server does not know the answer to a question, it queries 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) is used.
If port is * or is omitted, a random port number from a
pre-configured range is picked up and used for each query. The
port range(s) is 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 checks whether the operating system provides a programming
interface to retrieve the system’s default range for ephemeral ports. If
such an interface is available, named uses the corresponding
system default range; otherwise, it uses its own defaults:
use-v4-udp-ports { range 1024 65535; };
use-v6-udp-ports { range 1024 65535; };
The defaults of the avoid-v4-udp-ports and avoid-v6-udp-ports
options are:
avoid-v4-udp-ports {};
avoid-v6-udp-ports {};
Note
Make sure the ranges are sufficiently large for security. A
desirable size depends on several 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 is automatically applied when named is reloaded. Explicit
configuration of use-v4-udp-ports and use-v6-udp-ports is encouraged,
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 do not allow
named, if run without 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.
Note
The address specified in the query-source option is used for both
UDP and TCP queries, but the port applies only to UDP queries. TCP
queries always use a random unprivileged port.
Note
Solaris 2.5.1 and earlier does not support setting the source address for TCP sockets.
Note
See also transfer-source and notify-source.
4.2.14.7. Zone Transfers¶
BIND has mechanisms in place to facilitate zone transfers and set limits on the amount of load that transfers place on the system. The following options apply to zone transfers.
also-notifyThis option 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 quickly converge on stealth servers. Optionally, a port may be specified with each
also-notifyaddress to send the notify messages to a port other than the default of 53. An optional TSIG key can also be specified with each address to cause the notify messages to be signed; this can be useful when sending notifies to multiple views. In place of explicit addresses, one or more namedprimarieslists can be used.If an
also-notifylist is given in azonestatement, it overrides theoptions also-notifystatement. When azone notifystatement is set tono, the IP addresses in the globalalso-notifylist are not sent NOTIFY messages for that zone. The default is the empty list (no global notification list).max-transfer-time-inInbound zone transfers running longer than this many minutes are terminated. The default is 120 minutes (2 hours). The maximum value is 28 days (40320 minutes).
max-transfer-idle-inInbound zone transfers making no progress in this many minutes are terminated. The default is 60 minutes (1 hour). The maximum value is 28 days (40320 minutes).
max-transfer-time-outOutbound zone transfers running longer than this many minutes are terminated. The default is 120 minutes (2 hours). The maximum value is 28 days (40320 minutes).
max-transfer-idle-outOutbound zone transfers making no progress in this many minutes are terminated. The default is 60 minutes (1 hour). The maximum value is 28 days (40320 minutes).
notify-rateThis specifies the rate at which NOTIFY requests are sent during normal zone maintenance operations. (NOTIFY requests due to initial zone loading are subject to a separate rate limit; see below.) The default is 20 per second. The lowest possible rate is one per second; when set to zero, it is silently raised to one.
startup-notify-rateThis is the rate at which NOTIFY requests are sent when the name server is first starting up, or when zones have been newly added to the name server. The default is 20 per second. The lowest possible rate is one per second; when set to zero, it is silently raised to one.
serial-query-rateSecondary servers periodically query primary servers to find out if zone serial numbers have changed. Each such query uses a minute amount of the secondary 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-rateoption, an integer, is the maximum number of queries sent per second. The default is 20 per second. The lowest possible rate is one per second; when set to zero, it is silently raised to one.transfer-formatZone transfers can be sent using two different formats,
one-answerandmany-answers. Thetransfer-formatoption is used on the primary server to determine which format it sends.one-answeruses one DNS message per resource record transferred.many-answerspacks as many resource records as possible into one message.many-answersis more efficient; the default ismany-answers.transfer-formatmay be overridden on a per-server basis by using theserverstatement.transfer-message-sizeThis is an upper bound on the uncompressed size of DNS messages used in zone transfers over TCP. If a message grows larger than this size, additional messages are used to complete the zone transfer. (Note, however, that this is a hint, not a hard limit; if a message contains a single resource record whose RDATA does not fit within the size limit, a larger message will be permitted so the record can be transferred.)
Valid values are between 512 and 65535 octets; any values outside that range are adjusted to the nearest value within it. The default is
20480, which was selected to improve message compression; most DNS messages of this size will compress to less than 16536 bytes. Larger messages cannot be compressed as effectively, because 16536 is the largest permissible compression offset pointer in a DNS message.This option is mainly intended for server testing; there is rarely any benefit in setting a value other than the default.
transfers-inThis is the maximum number of inbound zone transfers that can run concurrently. The default value is
10. Increasingtransfers-inmay speed up the convergence of secondary zones, but it also may increase the load on the local system.transfers-outThis is the maximum number of outbound zone transfers that can run concurrently. Zone transfer requests in excess of the limit are refused. The default value is
10.transfers-per-nsThis is the maximum number of inbound zone transfers that can concurrently transfer from a given remote name server. The default value is
2. Increasingtransfers-per-nsmay speed up the convergence of secondary zones, but it also may increase the load on the remote name server.transfers-per-nsmay be overridden on a per-server basis by using thetransfersphrase of theserverstatement.transfer-sourcetransfer-sourcedetermines which local address is 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 is usually the address of the interface “closest to” the remote end. This address must appear in the remote end’sallow-transferoption for the zone being transferred, if one is specified. This statement sets thetransfer-sourcefor all zones, but can be overridden on a per-view or per-zone basis by including atransfer-sourcestatement within thevieworzoneblock in the configuration file.Note
Solaris 2.5.1 and earlier does not support setting the source address for TCP sockets.
transfer-source-v6This option is the same as
transfer-source, except zone transfers are performed using IPv6.alt-transfer-sourceThis indicates an alternate transfer source if the one listed in
transfer-sourcefails anduse-alt-transfer-sourceis set.Note
To avoid using the alternate transfer source, set
use-alt-transfer-sourceappropriately and do not depend upon getting an answer back to the first refresh query.alt-transfer-source-v6This indicates an alternate transfer source if the one listed in
transfer-source-v6fails anduse-alt-transfer-sourceis set.use-alt-transfer-sourceThis indicates whether the alternate transfer sources should be used. If views are specified, this defaults to
no; otherwise, it defaults toyes.notify-sourcenotify-sourcedetermines which local source address, and optionally UDP port, is used to send NOTIFY messages. This address must appear in the secondary server’sprimarieszone clause or in anallow-notifyclause. This statement sets thenotify-sourcefor all zones, but can be overridden on a per-zone or per-view basis by including anotify-sourcestatement within thezoneorviewblock in the configuration file.Note
Solaris 2.5.1 and earlier does not support setting the source address for TCP sockets.
notify-source-v6This option acts like
notify-source, but applies to notify messages sent to IPv6 addresses.
4.2.14.8. UDP Port Lists¶
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
are or are not used as source ports for UDP messages. See
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 are 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 a 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 pass through 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.
4.2.14.9. Operating System Resource Limits¶
The server’s usage of many system resources can be limited. Scaled
values are allowed when specifying resource limits. For example, 1G
can be used instead of 1073741824 to specify a limit of one
gigabyte. unlimited requests unlimited use, or the maximum available
amount. default uses the limit that was in force when the server was
started. See the description of size_spec in Configuration File Elements.
The following options set operating system resource limits for the name server process. Some operating systems do not support some or any of the limits; on such systems, a warning is issued if an unsupported limit is used.
coresizeThis sets the maximum size of a core dump. The default is
default.datasizeThis sets 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 to limit 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. To limit the amount of memory used by the server, use themax-cache-sizeandrecursive-clientsoptions instead.filesThis sets the maximum number of files the server may have open concurrently. The default is
unlimited.stacksizeThis sets the maximum amount of stack memory the server may use. The default is
default.
4.2.14.10. Server Resource Limits¶
The following options set limits on the server’s resource consumption that are enforced internally by the server rather than by the operating system.
max-journal-sizeThis sets a maximum size for each journal file (see The Journal File), expressed in bytes or, if followed by an optional unit suffix (‘k’, ‘m’, or ‘g’), in kilobytes, megabytes, or gigabytes. When the journal file approaches the specified size, some of the oldest transactions in the journal are automatically removed. The largest permitted value is 2 gigabytes. Very small values are rounded up to 4096 bytes. It is possible to specify
unlimited, which also means 2 gigabytes. If the limit is set todefaultor left unset, the journal is allowed to grow up to twice as large as the zone. (There is little benefit in storing larger journals.)This option may also be set on a per-zone basis.
max-recordsThis sets the maximum number of records permitted in a zone. The default is zero, which means the maximum is unlimited.
recursive-clientsThis sets the maximum number (a “hard quota”) of simultaneous recursive lookups the server performs 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 therecursive-clientsoption may have to be decreased on hosts with limited memory.recursive-clientsdefines a “hard quota” limit for pending recursive clients; when more clients than this are pending, new incoming requests are not accepted, and for each incoming request a previous pending request is dropped.A “soft quota” is also set. When this lower quota is exceeded, incoming requests are accepted, but for each one, a pending request is dropped. If
recursive-clientsis greater than 1000, the soft quota is set torecursive-clientsminus 100; otherwise it is set to 90% ofrecursive-clients.tcp-clientsThis is the maximum number of simultaneous client TCP connections that the server accepts. The default is
150.
clients-per-query;max-clients-per-queryThese set the initial value (minimum) and maximum number of recursive simultaneous clients for any given query (<qname,qtype,qclass>) that the server accepts before dropping additional clients.
namedattempts to self-tune this value and changes are 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 exceeds this value,
namedassumes that it is dealing with a non-responsive zone and drops additional queries. If it gets a response after dropping queries, it raises the estimate. The estimate is then lowered in 20 minutes if it has remained unchanged.If
clients-per-queryis set to zero, there is no limit on the number of clients per query and no queries are dropped.If
max-clients-per-queryis set to zero, there is no upper bound other than that imposed byrecursive-clients.fetches-per-zoneThis sets the maximum number of simultaneous iterative queries to any one domain that the server permits before blocking new queries for data in or beneath that zone. This value should reflect how many fetches would normally be sent to any one zone in the time it would take to resolve them. It should be smaller than
recursive-clients.When many clients simultaneously query for the same name and type, the clients are all attached to the same fetch, up to the
max-clients-per-querylimit, and only one iterative query is sent. However, when clients are simultaneously querying for different names or types, multiple queries are sent andmax-clients-per-queryis not effective as a limit.Optionally, this value may be followed by the keyword
droporfail, indicating whether queries which exceed the fetch quota for a zone are dropped with no response, or answered with SERVFAIL. The default isdrop.If
fetches-per-zoneis set to zero, there is no limit on the number of fetches per query and no queries are dropped. The default is zero.The current list of active fetches can be dumped by running
rndc recursing. The list includes the number of active fetches for each domain and the number of queries that have been passed or dropped as a result of thefetches-per-zonelimit. (Note: these counters are not cumulative over time; whenever the number of active fetches for a domain drops to zero, the counter for that domain is deleted, and the next time a fetch is sent to that domain, it is recreated with the counters set to zero.)fetches-per-serverThis sets the maximum number of simultaneous iterative queries that the server allows to be sent to a single upstream name server before blocking additional queries. This value should reflect how many fetches would normally be sent to any one server in the time it would take to resolve them. It should be smaller than
recursive-clients.Optionally, this value may be followed by the keyword
droporfail, indicating whether queries are dropped with no response or answered with SERVFAIL, when all of the servers authoritative for a zone are found to have exceeded the per-server quota. The default isfail.If
fetches-per-serveris set to zero, there is no limit on the number of fetches per query and no queries are dropped. The default is zero.The
fetches-per-serverquota is dynamically adjusted in response to detected congestion. As queries are sent to a server and either are answered or time out, an exponentially weighted moving average is calculated of the ratio of timeouts to responses. If the current average timeout ratio rises above a “high” threshold, thenfetches-per-serveris reduced for that server. If the timeout ratio drops below a “low” threshold, thenfetches-per-serveris increased. Thefetch-quota-paramsoptions can be used to adjust the parameters for this calculation.fetch-quota-paramsThis sets the parameters to use for dynamic resizing of the
fetches-per-serverquota in response to detected congestion.The first argument is an integer value indicating how frequently to recalculate the moving average of the ratio of timeouts to responses for each server. The default is 100, meaning that BIND recalculates the average ratio after every 100 queries have either been answered or timed out.
The remaining three arguments represent the “low” threshold (defaulting to a timeout ratio of 0.1), the “high” threshold (defaulting to a timeout ratio of 0.3), and the discount rate for the moving average (defaulting to 0.7). A higher discount rate causes recent events to weigh more heavily when calculating the moving average; a lower discount rate causes past events to weigh more heavily, smoothing out short-term blips in the timeout ratio. These arguments are all fixed-point numbers with precision of 1/100; at most two places after the decimal point are significant.
reserved-socketsThis sets the number of file descriptors reserved for TCP, stdio, etc. This needs to be big enough to cover the number of interfaces
namedlistens on plustcp-clients, as well as to provide room for outgoing TCP queries and incoming zone transfers. The default is512. The minimum value is128and the maximum value is128fewer than maxsockets (-S). This option may be removed in the future.This option has little effect on Windows.
max-cache-sizeThis sets the maximum amount of memory to use for the server’s cache, in bytes or percentage of total physical memory. When the amount of data in the cache reaches this limit, the server causes records to expire prematurely, following an LRU-based strategy, so that the limit is not exceeded. The keyword
unlimited, or the value 0, places no limit on the cache size; records are purged from the cache only when their TTLs expire. Any positive values less than 2MB are ignored and reset to 2MB. In a server with multiple views, the limit applies separately to the cache of each view. The default is90%. On systems where detection of the amount of physical memory is not supported, values represented as a percentage fall back to unlimited. Note that the detection of physical memory is done only once at startup, sonameddoes not adjust the cache size if the amount of physical memory is changed during runtime.tcp-listen-queueThis sets the listen-queue depth. The default and minimum is 10. If the kernel supports the accept filter “dataready”, this also controls how many TCP connections are queued in kernel space waiting for some data before being passed to accept. Non-zero values less than 10 are silently raised. A value of 0 may also be used; on most platforms this sets the listen-queue length to a system-defined default value.
tcp-initial-timeoutThis sets the amount of time (in units of 100 milliseconds) that the server waits on a new TCP connection for the first message from the client. The default is 300 (30 seconds), the minimum is 25 (2.5 seconds), and the maximum is 1200 (two minutes). Values above the maximum or below the minimum are adjusted with a logged warning. (Note: this value must be greater than the expected round-trip delay time; otherwise, no client will ever have enough time to submit a message.) This value can be updated at runtime by using
rndc tcp-timeouts.tcp-idle-timeoutThis sets the amount of time (in units of 100 milliseconds) that the server waits on an idle TCP connection before closing it, when the client is not using the EDNS TCP keepalive option. The default is 300 (30 seconds), the maximum is 1200 (two minutes), and the minimum is 1 (one-tenth of a second). Values above the maximum or below the minimum are adjusted with a logged warning. See
tcp-keepalive-timeoutfor clients using the EDNS TCP keepalive option. This value can be updated at runtime by usingrndc tcp-timeouts.tcp-keepalive-timeoutThis sets the amount of time (in units of 100 milliseconds) that the server waits on an idle TCP connection before closing it, when the client is using the EDNS TCP keepalive option. The default is 300 (30 seconds), the maximum is 65535 (about 1.8 hours), and the minimum is 1 (one-tenth of a second). Values above the maximum or below the minimum are adjusted with a logged warning. This value may be greater than
tcp-idle-timeoutbecause clients using the EDNS TCP keepalive option are expected to use TCP connections for more than one message. This value can be updated at runtime by usingrndc tcp-timeouts.tcp-advertised-timeoutThis sets the timeout value (in units of 100 milliseconds) that the server sends in responses containing the EDNS TCP keepalive option, which informs a client of the amount of time it may keep the session open. The default is 300 (30 seconds), the maximum is 65535 (about 1.8 hours), and the minimum is 0, which signals that the clients must close TCP connections immediately. Ordinarily this should be set to the same value as
tcp-keepalive-timeout. This value can be updated at runtime by usingrndc tcp-timeouts.
4.2.14.11. Periodic Task Intervals¶
heartbeat-intervalThe server performs zone maintenance tasks for all zones marked as
dialupwhenever 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 occurs.interface-intervalThe server scans the network interface list every
interface-intervalminutes. The default is 60 minutes; the maximum value is 28 days (40320 minutes). If set to 0, interface scanning only occurs when the configuration file is loaded, or whenautomatic-interface-scanis enabled and supported by the operating system. After the scan, the server begins listening for queries on any newly discovered interfaces (provided they are allowed by thelisten-onconfiguration), and stops listening on interfaces that have gone away. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.
4.2.14.12. The sortlist Statement¶
The response to a DNS query may consist of multiple resource records
(RRs) forming a resource record set (RRset). The name server
normally returns the RRs within the RRset in an indeterminate order (but
see the rrset-order statement in 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 in a special way. 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. When the addresses in the first
element overlap, the first rule to match is selected.
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 interpreted as a topology preference list. 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 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 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 only prefer other addresses on their directly connected networks.
sortlist {
// IF the local host
// THEN first fit on the following nets
{ localhost;
{ localnets;
192.168.1/24;
{ 192.168.2/24; 192.168.3/24; }; }; };
// IF on class C 192.168.1 THEN use .1, or .2 or .3
{ 192.168.1/24;
{ 192.168.1/24;
{ 192.168.2/24; 192.168.3/24; }; }; };
// IF on class C 192.168.2 THEN use .2, or .1 or .3
{ 192.168.2/24;
{ 192.168.2/24;
{ 192.168.1/24; 192.168.3/24; }; }; };
// IF on class C 192.168.3 THEN use .3, or .1 or .2
{ 192.168.3/24;
{ 192.168.3/24;
{ 192.168.1/24; 192.168.2/24; }; }; };
// IF .4 or .5 THEN prefer that net
{ { 192.168.4/24; 192.168.5/24; };
};
};
The following example illlustrates reasonable behavior for the local host and hosts on directly connected networks. Responses sent to queries from the local host favor any of the directly connected networks. Responses sent to queries from any other hosts on a directly connected network prefer addresses on that same network. Responses to other queries are not sorted.
sortlist {
{ localhost; localnets; };
{ localnets; };
};
4.2.14.13. RRset Ordering¶
Note
While alternating the order of records in a DNS response between subsequent queries is a known load distribution technique, certain caveats apply (mostly stemming from caching) which usually make it a suboptimal choice for load balancing purposes when used on its own.
The rrset-order statement permits configuration of the ordering of
the records in a multiple-record response. See also:
The sortlist Statement.
Each rule in an rrset-order statement is defined as follows:
[class <class_name>] [type <type_name>] [name "<domain_name>"] order <ordering>
The default qualifiers for each rule are:
If no
classis specified, the default isANY.If no
typeis specified, the default isANY.If no
nameis specified, the default is*(asterisk).
<domain_name> only matches the name itself, not any of its
subdomains. To make a rule match all subdomains of a given name, a
wildcard name (*.<domain_name>) must be used. Note that
*.<domain_name> does not match <domain_name> itself; to
specify RRset ordering for a name and all of its subdomains, two
separate rules must be defined: one for <domain_name> and one for
*.<domain_name>.
The legal values for <ordering> are:
fixedRecords are returned in the order they are defined in the zone file.
Note
The fixed option is only available if BIND is configured with
--enable-fixed-rrset at compile time.
randomRecords are returned in a random order.
cyclicRecords are returned in a cyclic round-robin order, rotating by one record per query.
noneRecords are returned in the order they were retrieved from the database. This order is indeterminate, but remains consistent as long as the database is not modified.
The default RRset order used depends on whether any rrset-order
statements are present in the configuration file used by named:
If no
rrset-orderstatement is present in the configuration file, the implicit default is to return all records inrandomorder.If any
rrset-orderstatements are present in the configuration file, but no ordering rule specified in these statements matches a given RRset, the default order for that RRset isnone.
Note that if multiple rrset-order statements are present in the
configuration file (at both the options and view levels), they
are not combined; instead, the more-specific one (view) replaces
the less-specific one (options).
If multiple rules within a single rrset-order statement match a
given RRset, the first matching rule is applied.
Example:
rrset-order {
type A name "foo.isc.org" order random;
type AAAA name "foo.isc.org" order cyclic;
name "bar.isc.org" order fixed;
name "*.bar.isc.org" order random;
name "*.baz.isc.org" order cyclic;
};
With the above configuration, the following RRset ordering is used:
QNAME |
QTYPE |
RRset Order |
|---|---|---|
|
|
|
|
|
|
|
|
|
|
all |
|
|
all |
|
|
all |
|
|
all |
|
|
all |
|
4.2.14.14. Tuning¶
lame-ttlThis 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 is1800(30 minutes).servfail-ttlThis sets the number of seconds to cache a SERVFAIL response due to DNSSEC validation failure or other general server failure. If set to
0, SERVFAIL caching is disabled. The SERVFAIL cache is not consulted if a query has the CD (Checking Disabled) bit set; this allows a query that failed due to DNSSEC validation to be retried without waiting for the SERVFAIL TTL to expire.The maximum value is
30seconds; any higher value is silently reduced. The default is1second.min-ncache-ttlTo reduce network traffic and increase performance, the server stores negative answers.
min-ncache-ttlis used to set a minimum retention time for these answers in the server, in seconds. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.The default
min-ncache-ttlis0seconds.min-ncache-ttlcannot exceed 90 seconds and is truncated to 90 seconds if set to a greater value.min-cache-ttlThis sets the minimum time for which the server caches ordinary (positive) answers, in seconds. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.
The default
min-cache-ttlis0seconds.min-cache-ttlcannot exceed 90 seconds and is truncated to 90 seconds if set to a greater value.max-ncache-ttlTo reduce network traffic and increase performance, the server stores negative answers.
max-ncache-ttlis used to set a maximum retention time for these answers in the server, in seconds. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.The default
max-ncache-ttlis 10800 seconds (3 hours).max-ncache-ttlcannot exceed 7 days and is silently truncated to 7 days if set to a greater value.max-cache-ttlThis sets the maximum time for which the server caches ordinary (positive) answers, in seconds. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.
The default
max-cache-ttlis 604800 (one week). 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.max-stale-ttlIf retaining stale RRsets in cache is enabled, and returning of stale cached answers is also enabled,
max-stale-ttlsets the maximum time for which the server retains records past their normal expiry to return them as stale records, when the servers for those records are not reachable. The default is 1 day. The minimum allowed is 1 second; a value of 0 is updated silently to 1 second.For stale answers to be returned, the retaining of them in cache must be enabled via the configuration option
stale-cache-enable, and returning cached answers must be enabled, either in the configuration file using thestale-answer-enableoption or by callingrndc serve-stale on.When
stale-cache-enableis set tono, setting themax-stale-ttlhas no effect, the value ofmax-cache-ttlwill be0in such case.resolver-nonbackoff-triesThis specifies how many retries occur before exponential backoff kicks in. The default is
3.resolver-retry-intervalThis sets the base retry interval in milliseconds. The default is
800.sig-validity-intervalThis specifies the number of days into the future that DNSSEC signatures that are automatically generated as a result of dynamic updates (Dynamic Update) will expire. There is an optional second field which specifies how long before expiry the signatures are regenerated. If not specified, the signatures are regenerated at 1/4 of the base interval. The second field is specified in days if the base interval is greater than 7 days; otherwise it is specified in hours. The default base interval is
30days, giving a re-signing interval of 7 1/2 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.
The
sig-validity-intervalcan be overridden for DNSKEY records by settingdnskey-sig-validity.The
sig-validity-intervalshould be at least several multiples of the SOA expire interval, to allow for reasonable interaction between the various timer and expiry dates.dnskey-sig-validityThis specifies the number of days into the future when DNSSEC signatures that are automatically generated for DNSKEY RRsets as a result of dynamic updates (Dynamic Update) will expire. If set to a non-zero value, this overrides the value set by
sig-validity-interval. The default is zero, meaningsig-validity-intervalis used. The maximum value is 3660 days (10 years), and higher values are rejected.sig-signing-nodesThis specifies the maximum number of nodes to be examined in each quantum, when signing a zone with a new DNSKEY. The default is
100.sig-signing-signaturesThis specifies a threshold number of signatures that terminates processing a quantum, when signing a zone with a new DNSKEY. The default is
10.sig-signing-typeThis specifies a private RDATA type to be used when generating signing-state records. The default is
65534.This parameter may be removed in a future version, once there is a standard type.
Signing-state records are used internally by
namedto track the current state of a zone-signing process, i.e., whether it is still active or has been completed. The records can be inspected using the commandrndc signing -list zone. Oncenamedhas finished signing a zone with a particular key, the signing-state record associated with that key can be removed from the zone by runningrndc signing -clear keyid/algorithm zone. To clear all of the completed signing-state records for a zone, userndc signing -clear all zone.min-refresh-time;max-refresh-time;min-retry-time;max-retry-timeThese 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, up to a hard-coded maximum expiry of 24 weeks. However, these values are set by the primary, giving secondary server administrators little control over their contents.
These options allow the administrator to set a minimum and maximum refresh and retry time in seconds per-zone, per-view, or globally. These options are valid for secondary and stub zones, and clamp the SOA refresh and retry times to the specified values.
The following defaults apply:
min-refresh-time300 seconds,max-refresh-time2419200 seconds (4 weeks),min-retry-time500 seconds, andmax-retry-time1209600 seconds (2 weeks).edns-udp-sizeThis sets the maximum advertised EDNS UDP buffer size, in bytes, to control the size of packets received from authoritative servers in response to recursive queries. Valid values are 512 to 4096; values outside this range are silently adjusted to the nearest value within it. The default value is 1232.
The usual reason for setting
edns-udp-sizeto a non-default value is to get UDP answers to pass through broken firewalls that block fragmented packets and/or block UDP DNS packets that are greater than 512 bytes.When
namedfirst queries a remote server, it advertises a UDP buffer size of 1232.Query timeouts observed for any given server affect the buffer size advertised in queries sent to that server. Depending on observed packet dropping patterns, the query is retried over TCP. Per-server EDNS statistics are only retained in memory for the lifetime of a given server’s ADB entry.
The
namednow sets the DON’T FRAGMENT flag on outgoing UDP packets. According to the measurements done by multiple parties this should not be causing any operational problems as most of the Internet “core” is able to cope with IP message sizes between 1400-1500 bytes, the 1232 size was picked as a conservative minimal number that could be changed by the DNS operator to a estimated path MTU minus the estimated header space. In practice, the smallest MTU witnessed in the operational DNS community is 1500 octets, the Ethernet maximum payload size, so a a useful default for maximum DNS/UDP payload size on reliable networks would be 1400.Any server-specific
edns-udp-sizesetting has precedence over all the above rules.max-udp-sizeThis sets the maximum EDNS UDP message size that
namedsends, in bytes. Valid values are 512 to 4096; values outside this range are silently adjusted to the nearest value within it. The default value is 1232.This value applies to responses sent by a server; to set the advertised buffer size in queries, see
edns-udp-size.The usual reason for setting
max-udp-sizeto a non-default value is to allow 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).Setting this to a low value encourages additional TCP traffic to the name server.
masterfile-formatThis specifies the file format of zone files (see Additional File Formats). The default value is
text, which is the standard textual representation, except for secondary zones, in which the default value israw. Files in formats other thantextare typically expected to be generated by thenamed-compilezonetool, or dumped bynamed.Note that when a zone file in a format other than
textis loaded,namedmay omit some of the checks which are performed for a file intextformat. In particular,check-nameschecks do not apply for therawformat. This means a zone file in therawformat must be generated with the same check level as that specified in thenamedconfiguration file. Also,mapformat files are loaded directly into memory via memory mapping, with only minimal checking.This statement sets the
masterfile-formatfor all zones, but can be overridden on a per-zone or per-view basis by including amasterfile-formatstatement within thezoneorviewblock in the configuration file.masterfile-styleThis specifies the formatting of zone files during dump, when the
masterfile-formatistext. This option is ignored with any othermasterfile-format.When set to
relative, records are printed in a multi-line format, with owner names expressed relative to a shared origin. When set tofull, records are printed in a single-line format with absolute owner names. Thefullformat is most suitable when a zone file needs to be processed automatically by a script. Therelativeformat is more human-readable, and is thus suitable when a zone is to be edited by hand. The default isrelative.max-recursion-depthThis sets the maximum number of levels of recursion that are permitted at any one time while servicing a recursive query. Resolving a name may require looking up a name server address, which in turn requires resolving another name, etc.; if the number of recursions exceeds this value, the recursive query is terminated and returns SERVFAIL. The default is 7.
max-recursion-queriesThis sets the maximum number of iterative queries that may be sent while servicing a recursive query. If more queries are sent, the recursive query is terminated and returns SERVFAIL. The default is 100.
notify-delayThis sets the delay, in seconds, between sending sets of NOTIFY messages for a zone. The default is 5 seconds.
The overall rate at which NOTIFY messages are sent for all zones is controlled by
serial-query-rate.max-rsa-exponent-sizeThis sets the maximum RSA exponent size, in bits, that is accepted when validating. Valid values are 35 to 4096 bits. The default, zero, is also accepted and is equivalent to 4096.
prefetchWhen a query is received for cached data which is to expire shortly,
namedcan refresh the data from the authoritative server immediately, ensuring that the cache always has an answer available.prefetchspecifies the “trigger” TTL value at which prefetch of the current query takes place; when a cache record with a lower TTL value is encountered during query processing, it is refreshed. Valid trigger TTL values are 1 to 10 seconds. Values larger than 10 seconds are silently reduced to 10. Setting a trigger TTL to zero causes prefetch to be disabled. The default trigger TTL is2.An optional second argument specifies the “eligibility” TTL: the smallest original TTL value that is accepted for a record to be eligible for prefetching. The eligibility TTL must be at least six seconds longer than the trigger TTL; if not,
namedsilently adjusts it upward. The default eligibility TTL is9.v6-biasWhen determining the next name server to try, this indicates by how many milliseconds to prefer IPv6 name servers. The default is
50milliseconds.
4.2.14.15. Built-in Server Information Zones¶
The server provides some helpful diagnostic information through a number
of built-in zones under the pseudo-top-level-domain bind in the
CHAOS class. These zones are part of a built-in view
(see view Statement Grammar) of class CHAOS, which is
separate from the default view of class IN. Most global
configuration options (allow-query, etc.) apply to this view,
but some are locally overridden: notify, recursion, and
allow-new-zones are always set to no, and rate-limit is set
to allow three responses per second.
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.
versionThis is the version the server should report via a query of the name
version.bindwith typeTXTand classCHAOS. The default is the real version number of this server. Specifyingversion nonedisables processing of the queries.Setting
versionto any value (includingnone) also disables queries forauthors.bind TXT CH.hostnameThis is the hostname the server should report via a query of the name
hostname.bindwith typeTXTand classCHAOS. This defaults to the hostname of the machine hosting the name server, as found by thegethostname()function. The primary purpose of such queries is to identify which of a group of anycast servers is actually answering the queries. Specifyinghostname none;disables processing of the queries.server-idThis is the ID the server should report when receiving a Name Server Identifier (NSID) query, or a query of the name
ID.SERVERwith typeTXTand classCHAOS. The primary purpose of such queries is to identify which of a group of anycast servers is actually answering the queries. Specifyingserver-id none;disables processing of the queries. Specifyingserver-id hostname;causesnamedto use the hostname as found by thegethostname()function. The defaultserver-idisnone.
4.2.14.16. Built-in Empty Zones¶
The named server has some built-in empty zones, for SOA and NS records
only. These are for zones that should normally be answered locally and for
which queries should not be sent to the Internet’s root servers. The
official servers that cover these namespaces return NXDOMAIN responses
to these queries. In particular, these cover the reverse namespaces for
addresses from RFC 1918, RFC 4193, RFC 5737, and RFC 6598. They also
include the reverse namespace for the IPv6 local address (locally assigned),
IPv6 link local addresses, the IPv6 loopback address, and the IPv6
unknown address.
The server attempts to determine if a built-in zone already exists or is active (covered by a forward-only forwarding declaration) and does not create an empty zone if either is true.
The current list of empty zones is:
10.IN-ADDR.ARPA
16.172.IN-ADDR.ARPA
17.172.IN-ADDR.ARPA
18.172.IN-ADDR.ARPA
19.172.IN-ADDR.ARPA
20.172.IN-ADDR.ARPA
21.172.IN-ADDR.ARPA
22.172.IN-ADDR.ARPA
23.172.IN-ADDR.ARPA
24.172.IN-ADDR.ARPA
25.172.IN-ADDR.ARPA
26.172.IN-ADDR.ARPA
27.172.IN-ADDR.ARPA
28.172.IN-ADDR.ARPA
29.172.IN-ADDR.ARPA
30.172.IN-ADDR.ARPA
31.172.IN-ADDR.ARPA
168.192.IN-ADDR.ARPA
64.100.IN-ADDR.ARPA
65.100.IN-ADDR.ARPA
66.100.IN-ADDR.ARPA
67.100.IN-ADDR.ARPA
68.100.IN-ADDR.ARPA
69.100.IN-ADDR.ARPA
70.100.IN-ADDR.ARPA
71.100.IN-ADDR.ARPA
72.100.IN-ADDR.ARPA
73.100.IN-ADDR.ARPA
74.100.IN-ADDR.ARPA
75.100.IN-ADDR.ARPA
76.100.IN-ADDR.ARPA
77.100.IN-ADDR.ARPA
78.100.IN-ADDR.ARPA
79.100.IN-ADDR.ARPA
80.100.IN-ADDR.ARPA
81.100.IN-ADDR.ARPA
82.100.IN-ADDR.ARPA
83.100.IN-ADDR.ARPA
84.100.IN-ADDR.ARPA
85.100.IN-ADDR.ARPA
86.100.IN-ADDR.ARPA
87.100.IN-ADDR.ARPA
88.100.IN-ADDR.ARPA
89.100.IN-ADDR.ARPA
90.100.IN-ADDR.ARPA
91.100.IN-ADDR.ARPA
92.100.IN-ADDR.ARPA
93.100.IN-ADDR.ARPA
94.100.IN-ADDR.ARPA
95.100.IN-ADDR.ARPA
96.100.IN-ADDR.ARPA
97.100.IN-ADDR.ARPA
98.100.IN-ADDR.ARPA
99.100.IN-ADDR.ARPA
100.100.IN-ADDR.ARPA
101.100.IN-ADDR.ARPA
102.100.IN-ADDR.ARPA
103.100.IN-ADDR.ARPA
104.100.IN-ADDR.ARPA
105.100.IN-ADDR.ARPA
106.100.IN-ADDR.ARPA
107.100.IN-ADDR.ARPA
108.100.IN-ADDR.ARPA
109.100.IN-ADDR.ARPA
110.100.IN-ADDR.ARPA
111.100.IN-ADDR.ARPA
112.100.IN-ADDR.ARPA
113.100.IN-ADDR.ARPA
114.100.IN-ADDR.ARPA
115.100.IN-ADDR.ARPA
116.100.IN-ADDR.ARPA
117.100.IN-ADDR.ARPA
118.100.IN-ADDR.ARPA
119.100.IN-ADDR.ARPA
120.100.IN-ADDR.ARPA
121.100.IN-ADDR.ARPA
122.100.IN-ADDR.ARPA
123.100.IN-ADDR.ARPA
124.100.IN-ADDR.ARPA
125.100.IN-ADDR.ARPA
126.100.IN-ADDR.ARPA
127.100.IN-ADDR.ARPA
0.IN-ADDR.ARPA
127.IN-ADDR.ARPA
254.169.IN-ADDR.ARPA
2.0.192.IN-ADDR.ARPA
100.51.198.IN-ADDR.ARPA
113.0.203.IN-ADDR.ARPA
255.255.255.255.IN-ADDR.ARPA
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA
8.B.D.0.1.0.0.2.IP6.ARPA
D.F.IP6.ARPA
8.E.F.IP6.ARPA
9.E.F.IP6.ARPA
A.E.F.IP6.ARPA
B.E.F.IP6.ARPA
EMPTY.AS112.ARPA
HOME.ARPA
Empty zones can be set 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, disable the root zone at the view level. For example:
disable-empty-zone ".";
If using the address ranges covered here, reverse zones covering the addresses should already be in place. 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 had to be deployed to channel the query load away from the infrastructure servers.
Note
The real parent servers for these zones should disable all empty zones under the parent zone they serve. For the real root servers, this is all built-in empty zones. This enables them to return referrals to deeper in the tree.
empty-serverThis specifies the server name that appears in the returned SOA record for empty zones. If none is specified, the zone’s name is used.
empty-contactThis specifies the contact name that appears in the returned SOA record for empty zones. If none is specified, “.” is used.
empty-zones-enableThis enables or disables all empty zones. By default, they are enabled.
disable-empty-zoneThis disables individual empty zones. By default, none are disabled. This option can be specified multiple times.
4.2.14.17. Content Filtering¶
BIND 9 provides the ability to filter out responses from external
DNS servers containing certain types of data in the answer section.
Specifically, it can reject address (A or AAAA) records if the
corresponding IPv4 or IPv6 addresses match the given
address_match_list of the deny-answer-addresses option. It can
also reject CNAME or DNAME records if the “alias” name (i.e., the CNAME
alias or the substituted query name due to DNAME) matches the given
namelist of the deny-answer-aliases option, where “match” means
the alias name is a subdomain of one of the name_list elements. If
the optional namelist is specified with except-from, records
whose query name matches the list are accepted regardless of the
filter setting. Likewise, if the alias name is a subdomain of the
corresponding zone, the deny-answer-aliases filter does not apply;
for example, even if “example.com” is specified for
deny-answer-aliases,
www.example.com. CNAME xxx.example.com.
returned by an “example.com” server is accepted.
In the address_match_list of the deny-answer-addresses option,
only ip_addr and ip_prefix are meaningful; any key_id is
silently ignored.
If a response message is rejected due to the filtering, the entire message is discarded without being cached, and a SERVFAIL error is returned to the client.
This filtering is intended to prevent “DNS rebinding attacks,” in which an attacker, in response to a query for a domain name the attacker controls, returns an IP address within the user’s own network or an alias name within the user’s own domain. A naive web browser or script could then serve as an unintended proxy, allowing the attacker to get access to an internal node of the local network that could not be externally accessed otherwise. See the paper available at https://dl.acm.org/doi/10.1145/1315245.1315298 for more details about these attacks.
For example, with a domain named “example.net” and an internal network using an IPv4 prefix 192.0.2.0/24, an administrator might specify the following rules:
deny-answer-addresses { 192.0.2.0/24; } except-from { "example.net"; };
deny-answer-aliases { "example.net"; };
If an external attacker let a web browser in the local network look up an IPv4 address of “attacker.example.com”, the attacker’s DNS server would return a response like this:
attacker.example.com. A 192.0.2.1
in the answer section. Since the rdata of this record (the IPv4 address) matches the specified prefix 192.0.2.0/24, this response would be ignored.
On the other hand, if the browser looked up a legitimate internal web server “www.example.net” and the following response were returned to the BIND 9 server:
www.example.net. A 192.0.2.2
it would be accepted, since the owner name “www.example.net” matches the
except-from element, “example.net”.
Note that this is not really an attack on the DNS per se. In fact, there is nothing wrong with having an “external” name mapped to an “internal” IP address or domain name from the DNS point of view; it might actually be provided for a legitimate purpose, such as for debugging. As long as the mapping is provided by the correct owner, it either is not possible or does not make sense to detect whether the intent of the mapping is legitimate within the DNS. The “rebinding” attack must primarily be protected at the application that uses the DNS. For a large site, however, it may be difficult to protect all possible applications at once. This filtering feature is provided only to help such an operational environment; turning it on is generally discouraged unless there is no other choice and the attack is a real threat to applications.
Care should be particularly taken if using this option for addresses within 127.0.0.0/8. These addresses are obviously “internal,” but many applications conventionally rely on a DNS mapping from some name to such an address. Filtering out DNS records containing this address spuriously can break such applications.
4.2.14.18. Response Policy Zone (RPZ) Rewriting¶
BIND 9 includes a limited mechanism to modify DNS responses for requests analogous to email anti-spam DNS rejection lists. Responses can be changed to deny the existence of domains (NXDOMAIN), deny the existence of IP addresses for domains (NODATA), or contain other IP addresses or data.
Response policy zones are named in the response-policy option for
the view, or among the global options if there is no response-policy
option for the view. Response policy zones are ordinary DNS zones
containing RRsets that can be queried normally if allowed. It is usually
best to restrict those queries with something like
allow-query { localhost; };. Note that zones using
masterfile-format map cannot be used as policy zones.
A response-policy option can support multiple policy zones. To
maximize performance, a radix tree is used to quickly identify response
policy zones containing triggers that match the current query. This
imposes an upper limit of 64 on the number of policy zones in a single
response-policy option; more than that is a configuration error.
Rules encoded in response policy zones are processed after those defined in Access Control. All queries from clients which are not permitted access to the resolver are answered with a status code of REFUSED, regardless of configured RPZ rules.
Five policy triggers can be encoded in RPZ records.
RPZ-CLIENT-IPIP records are triggered by the IP address of the DNS client. Client IP address triggers are encoded in records that have owner names that are subdomains of
rpz-client-ip, relativized to the policy zone origin name, and that encode an address or address block. IPv4 addresses are represented asprefixlength.B4.B3.B2.B1.rpz-client-ip. The IPv4 prefix length must be between 1 and 32. All four bytes - B4, B3, B2, and B1 - must be present. B4 is the decimal value of the least significant byte of the IPv4 address as in IN-ADDR.ARPA.IPv6 addresses are encoded in a format similar to the standard IPv6 text representation,
prefixlength.W8.W7.W6.W5.W4.W3.W2.W1.rpz-client-ip. Each of W8,…,W1 is a one- to four-digit hexadecimal number representing 16 bits of the IPv6 address as in the standard text representation of IPv6 addresses, but reversed as in IP6.ARPA. (Note that this representation of IPv6 addresses is different from IP6.ARPA, where each hex digit occupies a label.) All 8 words must be present except when one set of consecutive zero words is replaced with.zz., analogous to double colons (::) in standard IPv6 text encodings. The IPv6 prefix length must be between 1 and 128.QNAMEQNAME policy records are triggered by query names of requests and targets of CNAME records resolved to generate the response. The owner name of a QNAME policy record is the query name relativized to the policy zone.
RPZ-IPIP triggers are IP addresses in an A or AAAA record in the ANSWER section of a response. They are encoded like client-IP triggers, except as subdomains of
rpz-ip.RPZ-NSDNAMENSDNAME triggers match names of authoritative servers for the query name, a parent of the query name, a CNAME for the query name, or a parent of a CNAME. They are encoded as subdomains of
rpz-nsdname, relativized to the RPZ origin name. NSIP triggers match IP addresses in A and AAAA RRsets for domains that can be checked against NSDNAME policy records. Thensdname-enablephrase turns NSDNAME triggers off or on for a single policy zone or for all zones.If authoritative name servers for the query name are not yet known,
namedrecursively looks up the authoritative servers for the query name before applying an RPZ-NSDNAME rule, which can cause a processing delay. To speed up processing at the cost of precision, thensdname-wait-recurseoption can be used; when set tono, RPZ-NSDNAME rules are only applied when authoritative servers for the query name have already been looked up and cached. If authoritative servers for the query name are not in the cache, the RPZ-NSDNAME rule is ignored, but the authoritative servers for the query name are looked up in the background and the rule is applied to subsequent queries. The default isyes, meaning RPZ-NSDNAME rules are always applied, even if authoritative servers for the query name need to be looked up first.RPZ-NSIPNSIP triggers match the IP addresses of authoritative servers. They are encoded like IP triggers, except as subdomains of
rpz-nsip. NSDNAME and NSIP triggers are checked only for names with at leastmin-ns-dotsdots. The default value ofmin-ns-dotsis 1, to exclude top-level domains. Thensip-enablephrase turns NSIP triggers off or on for a single policy zone or for all zones.If a name server’s IP address is not yet known,
namedrecursively looks up the IP address before applying an RPZ-NSIP rule, which can cause a processing delay. To speed up processing at the cost of precision, thensip-wait-recurseoption can be used; when set tono, RPZ-NSIP rules are only applied when a name server’s IP address has already been looked up and cached. If a server’s IP address is not in the cache, the RPZ-NSIP rule is ignored, but the address is looked up in the background and the rule is applied to subsequent queries. The default isyes, meaning RPZ-NSIP rules are always applied, even if an address needs to be looked up first.
The query response is checked against all response policy zones, so two
or more policy records can be triggered by a response. Because DNS
responses are rewritten according to at most one policy record, a single
record encoding an action (other than DISABLED actions) must be
chosen. Triggers, or the records that encode them, are chosen for
rewriting in the following order:
Choose the triggered record in the zone that appears first in the response-policy option.
Prefer CLIENT-IP to QNAME to IP to NSDNAME to NSIP triggers in a single zone.
Among NSDNAME triggers, prefer the trigger that matches the smallest name under the DNSSEC ordering.
Among IP or NSIP triggers, prefer the trigger with the longest prefix.
Among triggers with the same prefix length, prefer the IP or NSIP trigger that matches the smallest IP address.
When the processing of a response is restarted to resolve DNAME or CNAME records and a policy record set has not been triggered, all response policy zones are again consulted for the DNAME or CNAME names and addresses.
RPZ record sets are any types of DNS record, except DNAME or DNSSEC, that
encode actions or responses to individual queries. Any of the policies
can be used with any of the triggers. For example, while the
TCP-only policy is commonly used with client-IP triggers, it can
be used with any type of trigger to force the use of TCP for responses
with owner names in a zone.
PASSTHRUThe auto-acceptance policy is specified by a CNAME whose target is
rpz-passthru. It causes the response to not be rewritten and is most often used to “poke holes” in policies for CIDR blocks.DROPThe auto-rejection policy is specified by a CNAME whose target is
rpz-drop. It causes the response to be discarded. Nothing is sent to the DNS client.TCP-OnlyThe “slip” policy is specified by a CNAME whose target is
rpz-tcp-only. It changes UDP responses to short, truncated DNS responses that require the DNS client to try again with TCP. It is used to mitigate distributed DNS reflection attacks.NXDOMAINThe “domain undefined” response is encoded by a CNAME whose target is the root domain (.).
NODATAThe empty set of resource records is specified by a CNAME whose target is the wildcard top-level domain (
*.). It rewrites the response to NODATA or ANCOUNT=0.Local DataA set of ordinary DNS records can be used to answer queries. Queries for record types not in the set are answered with NODATA.
A special form of local data is a CNAME whose target is a wildcard such as *.example.com. It is used as if an ordinary CNAME after the asterisk (*) has been replaced with the query name. This special form is useful for query logging in the walled garden’s authoritative DNS server.
All of the actions specified in all of the individual records in a
policy zone can be overridden with a policy clause in the
response-policy option. An organization using a policy zone provided
by another organization might use this mechanism to redirect domains to
its own walled garden.
GIVENThe placeholder policy says “do not override but perform the action specified in the zone.”
DISABLEDThe testing override policy causes policy zone records to do nothing but log what they would have done if the policy zone were not disabled. The response to the DNS query is written (or not) according to any triggered policy records that are not disabled. Disabled policy zones should appear first, because they are often not logged if a higher-precedence trigger is found first.
PASSTHRU;DROP;TCP-Only;NXDOMAIN;NODATAThese settings each override the corresponding per-record policy.
CNAME domainThis causes all RPZ policy records to act as if they were “cname domain” records.
By default, the actions encoded in a response policy zone are applied
only to queries that ask for recursion (RD=1). That default can be
changed for a single policy zone, or for all response policy zones in a view,
with a recursive-only no clause. This feature is useful for serving
the same zone files both inside and outside an RFC 1918 cloud and using
RPZ to delete answers that would otherwise contain RFC 1918 values on
the externally visible name server or view.
Also by default, RPZ actions are applied only to DNS requests that
either do not request DNSSEC metadata (DO=0) or when no DNSSEC records
are available for the requested name in the original zone (not the response
policy zone). This default can be changed for all response policy zones
in a view with a break-dnssec yes clause. In that case, RPZ actions
are applied regardless of DNSSEC. The name of the clause option reflects
the fact that results rewritten by RPZ actions cannot verify.
No DNS records are needed for a QNAME or Client-IP trigger; the name or
IP address itself is sufficient, so in principle the query name need not
be recursively resolved. However, not resolving the requested name can
leak the fact that response policy rewriting is in use, and that the name
is listed in a policy zone, to operators of servers for listed names. To
prevent that information leak, by default any recursion needed for a
request is done before any policy triggers are considered. Because
listed domains often have slow authoritative servers, this behavior can
cost significant time. The qname-wait-recurse yes option overrides
the default and enables that behavior when recursion cannot change a
non-error response. The option does not affect QNAME or client-IP
triggers in policy zones listed after other zones containing IP, NSIP,
and NSDNAME triggers, because those may depend on the A, AAAA, and NS
records that would be found during recursive resolution. It also does
not affect DNSSEC requests (DO=1) unless break-dnssec yes is in use,
because the response would depend on whether RRSIG records were
found during resolution. Using this option can cause error responses
such as SERVFAIL to appear to be rewritten, since no recursion is being
done to discover problems at the authoritative server.
The dnsrps-enable yes option turns on the DNS Response Policy Service
(DNSRPS) interface, if it has been compiled in named using
configure --enable-dnsrps.
The dnsrps-options block provides additional RPZ configuration
settings, which are passed through to the DNSRPS provider library.
Multiple DNSRPS settings in an dnsrps-options string should be
separated with semi-colons (;). The DNSRPS provider, librpz, is passed a
configuration string consisting of the dnsrps-options text,
concatenated with settings derived from the response-policy
statement.
Note: the dnsrps-options text should only include configuration
settings that are specific to the DNSRPS provider. For example, the
DNSRPS provider from Farsight Security takes options such as
dnsrpzd-conf, dnsrpzd-sock, and dnzrpzd-args (for details of
these options, see the librpz documentation). Other RPZ
configuration settings could be included in dnsrps-options as well,
but if named were switched back to traditional RPZ by setting
dnsrps-enable to “no”, those options would be ignored.
The TTL of a record modified by RPZ policies is set from the TTL of the
relevant record in the policy zone. It is then limited to a maximum value.
The max-policy-ttl clause changes the maximum number of seconds from its
default of 5. For convenience, TTL-style time-unit suffixes may be used
to specify the value. It also accepts ISO 8601 duration formats.
For example, an administrator might use this option statement:
response-policy { zone "badlist"; };
and this zone statement:
zone "badlist" {type primary; file "primary/badlist"; allow-query {none;}; };
with this zone file:
$TTL 1H
@ SOA LOCALHOST. named-mgr.example.com (1 1h 15m 30d 2h)
NS LOCALHOST.
; QNAME policy records. There are no periods (.) after the owner names.
nxdomain.domain.com CNAME . ; NXDOMAIN policy
*.nxdomain.domain.com CNAME . ; NXDOMAIN policy
nodata.domain.com CNAME *. ; NODATA policy
*.nodata.domain.com CNAME *. ; NODATA policy
bad.domain.com A 10.0.0.1 ; redirect to a walled garden
AAAA 2001:2::1
bzone.domain.com CNAME garden.example.com.
; do not rewrite (PASSTHRU) OK.DOMAIN.COM
ok.domain.com CNAME rpz-passthru.
; redirect x.bzone.domain.com to x.bzone.domain.com.garden.example.com
*.bzone.domain.com CNAME *.garden.example.com.
; IP policy records that rewrite all responses containing A records in 127/8
; except 127.0.0.1
8.0.0.0.127.rpz-ip CNAME .
32.1.0.0.127.rpz-ip CNAME rpz-passthru.
; NSDNAME and NSIP policy records
ns.domain.com.rpz-nsdname CNAME .
48.zz.2.2001.rpz-nsip CNAME .
; auto-reject and auto-accept some DNS clients
112.zz.2001.rpz-client-ip CNAME rpz-drop.
8.0.0.0.127.rpz-client-ip CNAME rpz-drop.
; force some DNS clients and responses in the example.com zone to TCP
16.0.0.1.10.rpz-client-ip CNAME rpz-tcp-only.
example.com CNAME rpz-tcp-only.
*.example.com CNAME rpz-tcp-only.
RPZ can affect server performance. Each configured response policy zone requires the server to perform one to four additional database lookups before a query can be answered. For example, a DNS server with four policy zones, each with all four kinds of response triggers (QNAME, IP, NSIP, and NSDNAME), requires a total of 17 times as many database lookups as a similar DNS server with no response policy zones. A BIND 9 server with adequate memory and one response policy zone with QNAME and IP triggers might achieve a maximum queries-per-second (QPS) rate about 20% lower. A server with four response policy zones with QNAME and IP triggers might have a maximum QPS rate about 50% lower.
Responses rewritten by RPZ are counted in the RPZRewrites
statistics.
The log clause can be used to optionally turn off rewrite logging
for a particular response policy zone. By default, all rewrites are
logged.
The add-soa option controls whether the RPZ’s SOA record is added to
the section for traceback of changes from this zone.
This can be set at the individual policy zone level or at the
response-policy level. The default is yes.
Updates to RPZ zones are processed asynchronously; if there is more than
one update pending they are bundled together. If an update to a RPZ zone
(for example, via IXFR) happens less than min-update-interval
seconds after the most recent update, the changes are not
carried out until this interval has elapsed. The default is 60
seconds. For convenience, TTL-style time-unit suffixes may be used to
specify the value. It also accepts ISO 8601 duration formats.
4.2.14.19. Response Rate Limiting¶
Excessive, almost-identical UDP responses can be controlled by
configuring a rate-limit clause in an options or view
statement. This mechanism keeps authoritative BIND 9 from being used to
amplify reflection denial-of-service (DoS) attacks. Short, truncated
(TC=1) responses can be sent to provide rate-limited responses to
legitimate clients within a range of forged, attacked IP addresses.
Legitimate clients react to dropped or truncated responses by retrying
with UDP or with TCP, respectively.
This mechanism is intended for authoritative DNS servers. It can be used on recursive servers, but can slow applications such as SMTP servers (mail receivers) and HTTP clients (web browsers) that repeatedly request the same domains. When possible, closing “open” recursive servers is better.
Response rate limiting uses a “credit” or “token bucket” scheme. Each
combination of identical response and client has a conceptual “account”
that earns a specified number of credits every second. A prospective
response debits its account by one. Responses are dropped or truncated
while the account is negative. Responses are tracked within a rolling
window of time which defaults to 15 seconds, but which can be configured with
the window option to any value from 1 to 3600 seconds (1 hour). The
account cannot become more positive than the per-second limit or more
negative than window times the per-second limit. When the specified
number of credits for a class of responses is set to 0, those responses
are not rate-limited.
The notions of “identical response” and “DNS client” for rate limiting
are not simplistic. All responses to an address block are counted as if
to a single client. The prefix lengths of address blocks are specified
with ipv4-prefix-length (default 24) and ipv6-prefix-length
(default 56).
All non-empty responses for a valid domain name (qname) and record type
(qtype) are identical and have a limit specified with
responses-per-second (default 0 or no limit). All empty (NODATA)
responses for a valid domain, regardless of query type, are identical.
Responses in the NODATA class are limited by nodata-per-second
(default responses-per-second). Requests for any and all undefined
subdomains of a given valid domain result in NXDOMAIN errors, and are
identical regardless of query type. They are limited by
nxdomains-per-second (default responses-per-second). This
controls some attacks using random names, but can be relaxed or turned
off (set to 0) on servers that expect many legitimate NXDOMAIN
responses, such as from anti-spam rejection lists. Referrals or delegations
to the server of a given domain are identical and are limited by
referrals-per-second (default responses-per-second).
Responses generated from local wildcards are counted and limited as if they were for the parent domain name. This controls flooding using random.wild.example.com.
All requests that result in DNS errors other than NXDOMAIN, such as
SERVFAIL and FORMERR, are identical regardless of requested name (qname)
or record type (qtype). This controls attacks using invalid requests or
distant, broken authoritative servers. By default the limit on errors is
the same as the responses-per-second value, but it can be set
separately with errors-per-second.
Many attacks using DNS involve UDP requests with forged source
addresses. Rate limiting prevents the use of BIND 9 to flood a network
with responses to requests with forged source addresses, but could let a
third party block responses to legitimate requests. There is a mechanism
that can answer some legitimate requests from a client whose address is
being forged in a flood. Setting slip to 2 (its default) causes
every other UDP request to be answered with a small truncated (TC=1)
response. The small size and reduced frequency, and resulting lack of
amplification, of “slipped” responses make them unattractive for
reflection DoS attacks. slip must be between 0 and 10. A value of 0
does not “slip”; no truncated responses are sent due to rate limiting. Rather,
all responses are dropped. A value of 1 causes every response to slip;
values between 2 and 10 cause every nth response to slip. Some error
responses, including REFUSED and SERVFAIL, cannot be replaced with
truncated responses and are instead leaked at the slip rate.
(Note: dropped responses from an authoritative server may reduce the
difficulty of a third party successfully forging a response to a
recursive resolver. The best security against forged responses is for
authoritative operators to sign their zones using DNSSEC and for
resolver operators to validate the responses. When this is not an
option, operators who are more concerned with response integrity than
with flood mitigation may consider setting slip to 1, causing all
rate-limited responses to be truncated rather than dropped. This reduces
the effectiveness of rate-limiting against reflection attacks.)
When the approximate query-per-second rate exceeds the qps-scale
value, the responses-per-second, errors-per-second,
nxdomains-per-second, and all-per-second values are reduced by
the ratio of the current rate to the qps-scale value. This feature
can tighten defenses during attacks. For example, with
qps-scale 250; responses-per-second 20; and a total query rate of
1000 queries/second for all queries from all DNS clients including via
TCP, then the effective responses/second limit changes to (250/1000)*20,
or 5. Responses sent via TCP are not limited but are counted to compute
the query-per-second rate.
Communities of DNS clients can be given their own parameters or no
rate limiting by putting rate-limit statements in view statements
instead of in the global option statement. A rate-limit statement
in a view replaces, rather than supplements, a rate-limit
statement among the main options. DNS clients within a view can be
exempted from rate limits with the exempt-clients clause.
UDP responses of all kinds can be limited with the all-per-second
phrase. This rate limiting is unlike the rate limiting provided by
responses-per-second, errors-per-second, and
nxdomains-per-second on a DNS server, which are often invisible to
the victim of a DNS reflection attack. Unless the forged requests of the
attack are the same as the legitimate requests of the victim, the
victim’s requests are not affected. Responses affected by an
all-per-second limit are always dropped; the slip value has no
effect. An all-per-second limit should be at least 4 times as large
as the other limits, because single DNS clients often send bursts of
legitimate requests. For example, the receipt of a single mail message
can prompt requests from an SMTP server for NS, PTR, A, and AAAA records
as the incoming SMTP/TCP/IP connection is considered. The SMTP server
can need additional NS, A, AAAA, MX, TXT, and SPF records as it
considers the SMTP Mail From command. Web browsers often repeatedly
resolve the same names that are duplicated in HTML <IMG> tags in a page.
all-per-second is similar to the rate limiting offered by firewalls
but is often inferior. Attacks that justify ignoring the contents of DNS
responses are likely to be attacks on the DNS server itself. They
usually should be discarded before the DNS server spends resources making
TCP connections or parsing DNS requests, but that rate limiting must be
done before the DNS server sees the requests.
The maximum size of the table used to track requests and rate-limit
responses is set with max-table-size. Each entry in the table is
between 40 and 80 bytes. The table needs approximately as many entries
as the number of requests received per second. The default is 20,000. To
reduce the cold start of growing the table, min-table-size (default 500)
can set the minimum table size. Enable rate-limit category
logging to monitor expansions of the table and inform choices for the
initial and maximum table size.
Use log-only yes to test rate-limiting parameters without actually
dropping any requests.
Responses dropped by rate limits are included in the RateDropped and
QryDropped statistics. Responses that are truncated by rate limits are
included in RateSlipped and RespTruncated.
4.2.14.20. NXDOMAIN Redirection¶
named supports NXDOMAIN redirection via two methods:
Redirect zone (zone Statement Grammar)
Redirect namespace
With either method, when named gets an NXDOMAIN response it examines a
separate namespace to see if the NXDOMAIN response should be replaced
with an alternative response.
With a redirect zone (zone "." { type redirect; };), the data used
to replace the NXDOMAIN is held in a single zone which is not part of
the normal namespace. All the redirect information is contained in the
zone; there are no delegations.
With a redirect namespace (option { nxdomain-redirect <suffix> };),
the data used to replace the NXDOMAIN is part of the normal namespace
and is looked up by appending the specified suffix to the original
query name. This roughly doubles the cache required to process
NXDOMAIN responses, as both the original NXDOMAIN response and the
replacement data (or an NXDOMAIN indicating that there is no
replacement) must be stored.
If both a redirect zone and a redirect namespace are configured, the redirect zone is tried first.
4.2.15. server Statement Grammar¶
server <netprefix> {
bogus <boolean>;
edns <boolean>;
edns-udp-size <integer>;
edns-version <integer>;
keys <server_key>;
max-udp-size <integer>;
notify-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [
dscp <integer> ];
notify-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * ) ]
[ dscp <integer> ];
padding <integer>;
provide-ixfr <boolean>;
query-source ( ( [ address ] ( <ipv4_address> | * ) [ port (
<integer> | * ) ] ) | ( [ [ address ] ( <ipv4_address> | * ) ]
port ( <integer> | * ) ) ) [ dscp <integer> ];
query-source-v6 ( ( [ address ] ( <ipv6_address> | * ) [ port (
<integer> | * ) ] ) | ( [ [ address ] ( <ipv6_address> | * ) ]
port ( <integer> | * ) ) ) [ dscp <integer> ];
request-expire <boolean>;
request-ixfr <boolean>;
request-nsid <boolean>;
send-cookie <boolean>;
tcp-keepalive <boolean>;
tcp-only <boolean>;
transfer-format ( many-answers | one-answer );
transfer-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [
dscp <integer> ];
transfer-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * )
] [ dscp <integer> ];
transfers <integer>;
};
4.2.16. server Statement Definition and Usage¶
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 a remote server is giving out bad data, marking it
as bogus prevents further queries to it. The default value of
bogus is no.
The provide-ixfr clause determines whether the local server, acting
as primary, responds with an incremental zone transfer when the given
remote server, a secondary, requests it. If set to yes, incremental
transfer is provided whenever possible. If set to no, all
transfers to the remote server are 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 secondary, requests incremental zone transfers from the given
remote server, a primary. If not set, the value of the request-ixfr
option in the view or global options block is used as a default. It may
also be set in the zone block; if set there, it overrides the
global or view setting for that zone.
IXFR requests to servers that do not support IXFR 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 primary and secondary claim to support it: for example, if
one of the servers is buggy and crashes or corrupts data when IXFR is
used.
The request-expire clause determines whether the local server, when
acting as a secondary, requests the EDNS EXPIRE value. The EDNS EXPIRE
value indicates the remaining time before the zone data expires and
needs to be refreshed. This is used when a secondary server transfers
a zone from another secondary server; when transferring from the
primary, the expiration timer is set from the EXPIRE field of the SOA
record instead. The default is yes.
The edns clause determines whether the local server attempts 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 are silently adjusted to the
nearest value within it. This option is useful when
advertising a different value to this server than the value advertised
globally: for example, when there is a firewall at the remote site that
is blocking large replies. Note: currently, this sets a single UDP size
for all packets sent to the server; named does not deviate from this
value. This differs from the behavior of edns-udp-size in
options or view statements, where it specifies a maximum value.
The server statement behavior may be brought into conformance with
the options/view behavior in future releases.
The edns-version option sets the maximum EDNS VERSION that is
sent to the server(s) by the resolver. The actual EDNS version sent is
still subject to normal EDNS version-negotiation rules (see RFC 6891),
the maximum EDNS version supported by the server, and any other
heuristics that indicate that a lower version should be sent. This
option is intended to be used when a remote server reacts badly to a
given EDNS version or higher; it should be set to the highest version
the remote server is known to support. Valid values are 0 to 255; higher
values are silently adjusted. This option is not needed until
higher EDNS versions than 0 are in use.
The max-udp-size option sets the maximum EDNS UDP message size
named sends. Valid values are 512 to 4096 bytes; values outside
this range are silently adjusted. This option is useful when
there is a firewall that is blocking large replies from
named.
The padding option adds EDNS Padding options to outgoing messages,
increasing the packet size to a multiple of the specified block size.
Valid block sizes range from 0 (the default, which disables the use of
EDNS Padding) to 512 bytes. Larger values are reduced to 512, with a
logged warning. Note: this option is not currently compatible with no
TSIG or SIG(0), as the EDNS OPT record containing the padding would have
to be added to the packet after it had already been signed.
The tcp-only option sets the transport protocol to TCP. The default
is to use the UDP transport and to fallback on TCP only when a truncated
response is received.
The tcp-keepalive option adds EDNS TCP keepalive to messages sent
over TCP. Note that currently idle timeouts in responses are ignored.
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 single
message, which is more efficient.
It is possible to specify which method to use for a server via the
transfer-format option; if not set there, the
transfer-format specified by the options statement is 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 (see TSIG)
when talking to the remote server. When a request is sent to the remote
server, a request signature is 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.
Only a single key per server is currently supported.
The transfer-source and transfer-source-v6 clauses specify the
IPv4 and IPv6 source address, respectively, to be used for zone transfer with the
remote server. 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
Zone Transfers.
The notify-source and notify-source-v6 clauses specify the IPv4
and IPv6 source address, respectively, to be used for notify messages sent to remote
servers. 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, respectively, to be used for queries sent to remote servers.
For an IPv4 remote server, only query-source can be
specified. Similarly, for an IPv6 remote server, only
query-source-v6 can be specified.
The request-nsid clause determines whether the local server adds
an NSID EDNS option to requests sent to the server. This overrides
request-nsid set at the view or option level.
The send-cookie clause determines whether the local server adds
a COOKIE EDNS option to requests sent to the server. This overrides
send-cookie set at the view or option level. The named server
may determine that COOKIE is not supported by the remote server and not
add a COOKIE EDNS option to requests.
4.2.17. statistics-channels Statement Grammar¶
statistics-channels {
inet ( <ipv4_address> | <ipv6_address> |
* ) [ port ( <integer> | * ) ] [
allow { <address_match_element>; ...
} ];
};
4.2.18. statistics-channels Statement Definition and Usage¶
The statistics-channels statement declares communication channels to
be used by system administrators to get access to statistics information
on the name server.
This statement is intended to be flexible to support multiple communication
protocols in the future, but currently only HTTP access is supported. It
requires that BIND 9 be compiled with libxml2 and/or json-c (also known
as libjson0); the statistics-channels statement is still accepted
even if it is built without the library, but any HTTP access fails
with an error.
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 are accepted on any of the system’s
IPv4 addresses. To listen on the IPv6 wildcard address, use an
ip_addr of ::.
If no port is specified, port 80 is used for HTTP channels. The asterisk
(*) cannot be used for ip_port.
Attempts to open a statistics channel are restricted by the
optional allow clause. Connections to the statistics channel are
permitted based on the address_match_list. If no allow clause is
present, named accepts connection attempts from any address; since
the statistics may contain sensitive internal information, it is highly
recommended to restrict the source of connection requests appropriately.
If no statistics-channels statement is present, named does not
open any communication channels.
The statistics are available in various formats and views, depending on the URI used to access them. For example, if the statistics channel is configured to listen on 127.0.0.1 port 8888, then the statistics are accessible in XML format at http://127.0.0.1:8888/ or http://127.0.0.1:8888/xml. A CSS file is included, which can format the XML statistics into tables when viewed with a stylesheet-capable browser, and into charts and graphs using the Google Charts API when using a JavaScript-capable browser.
Broken-out subsets of the statistics can be viewed at http://127.0.0.1:8888/xml/v3/status (server uptime and last reconfiguration time), http://127.0.0.1:8888/xml/v3/server (server and resolver statistics), http://127.0.0.1:8888/xml/v3/zones (zone statistics), http://127.0.0.1:8888/xml/v3/net (network status and socket statistics), http://127.0.0.1:8888/xml/v3/mem (memory manager statistics), http://127.0.0.1:8888/xml/v3/tasks (task manager statistics), and http://127.0.0.1:8888/xml/v3/traffic (traffic sizes).
The full set of statistics can also be read in JSON format at http://127.0.0.1:8888/json, with the broken-out subsets at http://127.0.0.1:8888/json/v1/status (server uptime and last reconfiguration time), http://127.0.0.1:8888/json/v1/server (server and resolver statistics), http://127.0.0.1:8888/json/v1/zones (zone statistics), http://127.0.0.1:8888/json/v1/net (network status and socket statistics), http://127.0.0.1:8888/json/v1/mem (memory manager statistics), http://127.0.0.1:8888/json/v1/tasks (task manager statistics), and http://127.0.0.1:8888/json/v1/traffic (traffic sizes).
4.2.19. tls Statement Grammar¶
tls <string> {
ca-file <quoted_string>;
cert-file <quoted_string>;
ciphers <string>; // experimental
dh-param <quoted_string>; // experimental
hostname <quoted_string>;
key-file <quoted_string>;
protocols <sslprotos>; // experimental
};
4.2.20. tls Statement Definition and Usage¶
The tls statement is used to configure a TLS connection; this
configuration can then be referenced by a listen-on or listen-on-v6
statement to cause named to listen for incoming requests via TLS,
or in the primaries statement for a zone of type secondary to
cause zone transfer requests to be sent via TLS.
tls can only be set at the top level of named.conf.
The following options can be specified in a tls statement:
key-filePath to a file containing the private TLS key to be used for the connection.
cert-filePath to a file containing the TLS certificate to be used for the connection.
ca-filePath to a file containing trusted TLS certificates.
hostnameThe hostname associated with the certificate.
There are two built-in TLS connection configurations: ephemeral,
uses a temporary key and certificate created for the current named
session only, and none, which can be used when setting up an HTTP
listener with no encryption.
4.2.21. http Statement Grammar¶
http <string> {
endpoints { <quoted_string>; ... };
};
4.2.22. http Statement Definition and Usage¶
The http statement is used to configure HTTP endpoints on which
to listen for DNS-over-HTTPS (DoH) queries. This configuration can
then be referenced by a listen-on or listen-on-v6 statement to
cause named to listen for incoming requests over HTTPS.
http can only be set at the top level of named.conf.
The following options can be specified in an http statement:
endpointsA list of HTTP query paths on which to listen. A typical path is “/dns-query”.
for example, the following configuration enables DNS-over-HTTPS queries on all local addresses:
http local {
endpoints { "/dns-query"; };
};
options {
....
listen-on tls ephemeral http local { any; };
listen-on-v6 tls ephemeral http local { any; };
};
4.2.23. trust-anchors Statement Grammar¶
trust-anchors { <string> ( static-key |
initial-key | static-ds | initial-ds )
<integer> <integer> <integer>
<quoted_string>; ... };
4.2.24. trust-anchors Statement Definition and Usage¶
The trust-anchors statement defines DNSSEC trust anchors. DNSSEC is
described in DNSSEC.
A trust anchor is defined when the public key or public key digest 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 or digest has been configured as a trust anchor, it is treated as if it has been validated and proven secure.
The resolver attempts DNSSEC validation on all DNS data in subdomains of
configured trust anchors. Validation below specified names can be
temporarily disabled by using rndc nta, or permanently disabled with
the validate-except option.
All keys listed in trust-anchors, and their corresponding zones, are
deemed to exist regardless of what parent zones say. Only keys
configured as trust anchors are used to validate the DNSKEY RRset for
the corresponding name. The parent’s DS RRset is not used.
trust-anchors may be set at the top level of named.conf or within
a view. If it is set in both places, the configurations are additive;
keys defined at the top level are inherited by all views, but keys
defined in a view are only used within that view.
The trust-anchors statement can contain
multiple trust-anchor entries, each consisting of a
domain name, followed by an “anchor type” keyword indicating
the trust anchor’s format, followed by the key or digest data.
If the anchor type is static-key or
initial-key, then it is followed with the
key’s flags, protocol, and algorithm, plus the Base64 representation
of the public key data. This is identical to the text
representation of a DNSKEY record. Spaces, tabs, newlines, and
carriage returns are ignored in the key data, so the
configuration may be split into multiple lines.
If the anchor type is static-ds or
initial-ds, it is followed with the
key tag, algorithm, digest type, and the hexadecimal
representation of the key digest. This is identical to the
text representation of a DS record. Spaces, tabs, newlines,
and carriage returns are ignored.
Trust anchors configured with the
static-key or static-ds
anchor types are immutable, while keys configured with
initial-key or initial-ds
can be kept up-to-date automatically, without intervention from the resolver operator.
(static-key keys are identical to keys configured using the
deprecated trusted-keys statement.)
Suppose, for example, that a zone’s key-signing key was compromised, and
the zone owner had to revoke and replace the key. A resolver which had
the original key
configured using static-key or
static-ds would be unable to validate
this zone any longer; it would reply with a SERVFAIL response
code. This would continue until the resolver operator had
updated the trust-anchors statement with
the new key.
If, however, the trust anchor had been configured using
initial-key or initial-ds
instead, the zone owner could add a “stand-by” key to
the zone in advance. named would store
the stand-by key, and when the original key was revoked,
named would be able to transition smoothly
to the new key. It would also recognize that the old key had
been revoked and cease using that key to validate answers,
minimizing the damage that the compromised key could do.
This is the process used to keep the ICANN root DNSSEC key
up-to-date.
Whereas static-key and
static-ds trust anchors continue
to be trusted until they are removed from
named.conf, an
initial-key or initial-ds
is only trusted once: for as long as it
takes to load the managed key database and start the
RFC 5011 key maintenance process.
It is not possible to mix static with initial trust anchors for the same domain name.
The first time named runs with an
initial-key or initial-ds
configured in named.conf, it fetches the
DNSKEY RRset directly from the zone apex,
and validates it
using the trust anchor specified in trust-anchors.
If the DNSKEY RRset is validly signed by a key matching
the trust anchor, then it is used as the basis for a new
managed-keys database.
From that point on, whenever named runs, it sees the initial-key or initial-ds
listed in trust-anchors, checks to make sure RFC 5011 key maintenance
has already been initialized for the specified domain, and if so,
simply moves on. The key specified in the trust-anchors statement is
not used to validate answers; it is superseded by the key or keys stored
in the managed-keys database.
The next time named runs after an initial-key or initial-ds has been removed
from the trust-anchors statement (or changed to a static-key or static-ds), the
corresponding zone is removed from the managed-keys database, and
RFC 5011 key maintenance is no longer used for that domain.
In the current implementation, the managed-keys database is stored as a master-format zone file.
On servers which do not use views, this file is named
managed-keys.bind. When views are in use, there is a separate
managed-keys database for each view; the filename is the view name
(or, if a view name contains characters which would make it illegal as a
filename, a hash of the view name), followed by the suffix .mkeys.
When the key database is changed, the zone is updated. As with any other
dynamic zone, changes are written into a journal file, e.g.,
managed-keys.bind.jnl or internal.mkeys.jnl. Changes are
committed to the primary file as soon as possible afterward,
usually within 30 seconds. Whenever named is using
automatic key maintenance, the zone file and journal file can be
expected to exist in the working directory. (For this reason, among
others, the working directory should be always be writable by
named.)
If the dnssec-validation option is set to auto, named
automatically initializes an initial-key for the root zone. The key
that is used to initialize the key-maintenance process is stored in
bind.keys; the location of this file can be overridden with the
bindkeys-file option. As a fallback in the event no bind.keys
can be found, the initializing key is also compiled directly into
named.
4.2.25. dnssec-policy Statement Grammar¶
dnssec-policy <string> {
dnskey-ttl <duration>;
keys { ( csk | ksk | zsk ) [ ( key-directory ) ] lifetime
<duration_or_unlimited> algorithm <string> [ <integer> ]; ... };
max-zone-ttl <duration>;
nsec3param [ iterations <integer> ] [ optout <boolean> ] [
salt-length <integer> ];
parent-ds-ttl <duration>;
parent-propagation-delay <duration>;
publish-safety <duration>;
purge-keys <duration>;
retire-safety <duration>;
signatures-refresh <duration>;
signatures-validity <duration>;
signatures-validity-dnskey <duration>;
zone-propagation-delay <duration>;
};
4.2.26. dnssec-policy Statement Definition and Usage¶
The dnssec-policy statement defines a key and signing policy (KASP)
for zones.
A KASP determines how one or more zones are signed with DNSSEC. For example, it specifies how often keys should roll, which cryptographic algorithms to use, and how often RRSIG records need to be refreshed.
Keys are not shared among zones, which means that one set of keys per zone is generated even if they have the same policy. If multiple views are configured with different versions of the same zone, each separate version uses the same set of signing keys.
Multiple key and signing policies can be configured. To attach a policy
to a zone, add a dnssec-policy option to the zone statement,
specifying the name of the policy that should be used.
Key rollover timing is computed for each key according to the key
lifetime defined in the KASP. The lifetime may be modified by zone TTLs
and propagation delays, to prevent validation failures. When a key
reaches the end of its lifetime, named generates and publishes a new
key automatically, then deactivates the old key and activates the new
one; finally, the old key is retired according to a computed schedule.
Zone-signing key (ZSK) rollovers require no operator input. Key-signing key (KSK) and combined-signing key (CSK) rollovers require action to be taken to submit a DS record to the parent. Rollover timing for KSKs and CSKs is adjusted to take into account delays in processing and propagating DS updates.
There are two predefined dnssec-policy names: none and
default. Setting a zone’s policy to none is the same as not
setting dnssec-policy at all; the zone is not signed. Policy
default causes the zone to be signed with a single combined-signing
key (CSK) using algorithm ECDSAP256SHA256; this key has an unlimited
lifetime. (A verbose copy of this policy may be found in the source
tree, in the file doc/misc/dnssec-policy.default.conf.)
Note
The default signing policy may change in future releases.
This could require changes to a signing policy when upgrading to a
new version of BIND. Check the release notes carefully when
upgrading to be informed of such changes. To prevent policy changes
on upgrade, use an explicitly defined dnssec-policy, rather than
default.
If a dnssec-policy statement is modified and the server restarted or
reconfigured, named attempts to change the policy smoothly from the
old one to the new. For example, if the key algorithm is changed, then
a new key is generated with the new algorithm, and the old algorithm is
retired when the existing key’s lifetime ends.
Note
Rolling to a new policy while another key rollover is already in progress is not yet supported, and may result in unexpected behavior.
The following options can be specified in a dnssec-policy statement:
dnskey-ttlThis indicates the TTL to use when generating DNSKEY resource records. The default is 1 hour (3600 seconds).
keysThis is a list specifying the algorithms and roles to use when generating keys and signing the zone. Entries in this list do not represent specific DNSSEC keys, which may be changed on a regular basis, but the roles that keys play in the signing policy. For example, configuring a KSK of algorithm RSASHA256 ensures that the DNSKEY RRset always includes a key-signing key for that algorithm.
Here is an example (for illustration purposes only) of some possible entries in a
keyslist:keys { ksk key-directory lifetime unlimited algorithm rsasha1 2048; zsk lifetime P30D algorithm 8; csk lifetime P6MT12H3M15S algorithm ecdsa256; };This example specifies that three keys should be used in the zone. The first token determines which role the key plays in signing RRsets. If set to
ksk, then this is a key-signing key; it has the KSK flag set and is only used to sign DNSKEY, CDS, and CDNSKEY RRsets. If set tozsk, this is a zone-signing key; the KSK flag is unset, and the key signs all RRsets except DNSKEY, CDS, and CDNSKEY. If set tocsk, the key has the KSK flag set and is used to sign all RRsets.An optional second token determines where the key is stored. Currently, keys can only be stored in the configured
key-directory. This token may be used in the future to store keys in hardware service modules or separate directories.The
lifetimeparameter specifies how long a key may be used before rolling over. In the example above, the first key has an unlimited lifetime, the second key may be used for 30 days, and the third key has a rather peculiar lifetime of 6 months, 12 hours, 3 minutes, and 15 seconds. A lifetime of 0 seconds is the same asunlimited.Note that the lifetime of a key may be extended if retiring it too soon would cause validation failures. For example, if the key were configured to roll more frequently than its own TTL, its lifetime would automatically be extended to account for this.
The
algorithmparameter specifies the key’s algorithm, expressed either as a string (“rsasha256”, “ecdsa384”, etc.) or as a decimal number. An optional second parameter specifies the key’s size in bits. If it is omitted, as shown in the example for the second and third keys, an appropriate default size for the algorithm is used.purge-keysThis is the time after when DNSSEC keys that have been deleted from the zone can be removed from disk. If a key still determined to have presence (for example in some resolver cache),
namedwill not remove the key files.The default is
P90D(90 days). Set this option to0to never purge deleted keys.publish-safetyThis is a margin that is added to the pre-publication interval in rollover timing calculations, to give some extra time to cover unforeseen events. This increases the time between when keys are published and when they become active. The default is
PT1H(1 hour).retire-safetyThis is a margin that is added to the post-publication interval in rollover timing calculations, to give some extra time to cover unforeseen events. This increases the time a key remains published after it is no longer active. The default is
PT1H(1 hour).signatures-refreshThis determines how frequently an RRSIG record needs to be refreshed. The signature is renewed when the time until the expiration time is less than the specified interval. The default is
P5D(5 days), meaning signatures that expire in 5 days or sooner are refreshed.signatures-validityThis indicates the validity period of an RRSIG record (subject to inception offset and jitter). The default is
P2W(2 weeks).signatures-validity-dnskeyThis is similar to
signatures-validity, but for DNSKEY records. The default isP2W(2 weeks).max-zone-ttlLike the
max-zone-ttlzone option, this specifies the maximum permissible TTL value, in seconds, for the zone. When loading a zone file using amasterfile-formatoftextorraw, any record encountered with a TTL higher thanmax-zone-ttlis capped at the maximum permissible TTL value.This is needed in DNSSEC-maintained zones because when rolling to a new DNSKEY, the old key needs to remain available until RRSIG records have expired from caches. The
max-zone-ttloption guarantees that the largest TTL in the zone is no higher than the set value.Note
Because
map-format files load directly into memory, this option cannot be used with them.The default value is
PT24H(24 hours). Amax-zone-ttlof zero is treated as if the default value were in use.nsec3paramUse NSEC3 instead of NSEC, and optionally set the NSEC3 parameters.
Here is an example of an
nsec3configuration:nsec3param iterations 5 optout no salt-length 8;The default is to use NSEC. The
iterations,optoutandsalt-lengthparts are optional, but if not set, the values in the example above are the default NSEC3 parameters.zone-propagation-delayThis is the expected propagation delay from the time when a zone is first updated to the time when the new version of the zone is served by all secondary servers. The default is
PT5M(5 minutes).parent-ds-ttlThis is the TTL of the DS RRset that the parent zone uses. The default is
P1D(1 day).parent-propagation-delayThis is the expected propagation delay from the time when the parent zone is updated to the time when the new version is served by all of the parent zone’s name servers. The default is
PT1H(1 hour).
4.2.27. managed-keys Statement Grammar¶
managed-keys { <string> ( static-key
| initial-key | static-ds |
initial-ds ) <integer> <integer>
<integer> <quoted_string>; ... };, deprecated
4.2.28. managed-keys Statement Definition and Usage¶
The managed-keys statement has been
deprecated in favor of trust-anchors Statement Grammar
with the initial-key keyword.
4.2.29. trusted-keys Statement Grammar¶
trusted-keys { <string> <integer>
<integer> <integer>
<quoted_string>; ... };, deprecated
4.2.30. trusted-keys Statement Definition and Usage¶
The trusted-keys statement has been deprecated in favor of
trust-anchors Statement Grammar with the static-key keyword.
4.2.31. view Statement Grammar¶
view view_name [ class ] {
match-clients { address_match_list } ;
match-destinations { address_match_list } ;
match-recursive-only yes_or_no ;
[ view_option ; ... ]
[ zone_statement ; ... ]
} ;
4.2.32. view Statement Definition and Usage¶
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 is
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 match that view. The order
of the view statements is significant; a client request is
resolved in the context of the first view that it matches.
Zones defined within a view statement are only 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 applies 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 primary;
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 primary;
file "example-external.db";
};
};
4.2.33. zone Statement Grammar¶
zone <string> [ <class> ] {
type ( master | primary );
allow-query { <address_match_element>; ... };
allow-query-on { <address_match_element>; ... };
allow-transfer { <address_match_element>; ... };
allow-update { <address_match_element>; ... };
also-notify [ port <integer> ] [ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
alt-transfer-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
alt-transfer-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
auto-dnssec ( allow | maintain | off );
check-dup-records ( fail | warn | ignore );
check-integrity <boolean>;
check-mx ( fail | warn | ignore );
check-mx-cname ( fail | warn | ignore );
check-names ( fail | warn | ignore );
check-sibling <boolean>;
check-spf ( warn | ignore );
check-srv-cname ( fail | warn | ignore );
check-wildcard <boolean>;
database <string>;
dialup ( notify | notify-passive | passive | refresh | <boolean> );
dlz <string>;
dnskey-sig-validity <integer>;
dnssec-dnskey-kskonly <boolean>;
dnssec-loadkeys-interval <integer>;
dnssec-policy <string>;
dnssec-secure-to-insecure <boolean>;
dnssec-update-mode ( maintain | no-resign );
file <quoted_string>;
forward ( first | only );
forwarders [ port <integer> ] [ dscp <integer> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ dscp <integer> ]; ... };
inline-signing <boolean>;
ixfr-from-differences <boolean>;
journal <quoted_string>;
key-directory <quoted_string>;
masterfile-format ( map | raw | text );
masterfile-style ( full | relative );
max-ixfr-ratio ( unlimited | <percentage> );
max-journal-size ( default | unlimited | <sizeval> );
max-records <integer>;
max-transfer-idle-out <integer>;
max-transfer-time-out <integer>;
max-zone-ttl ( unlimited | <duration> );
notify ( explicit | master-only | primary-only | <boolean> );
notify-delay <integer>;
notify-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
notify-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
notify-to-soa <boolean>;
serial-update-method ( date | increment | unixtime );
sig-signing-nodes <integer>;
sig-signing-signatures <integer>;
sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ];
update-check-ksk <boolean>;
update-policy ( local | { ( deny | grant ) <string> ( 6to4-self | external | krb5-self | krb5-selfsub | krb5-subdomain | ms-self | ms-selfsub | ms-subdomain | name | self | selfsub | selfwild | subdomain | tcp-self | wildcard | zonesub ) [ <string> ] <rrtypelist>; ... };
zero-no-soa-ttl <boolean>;
zone-statistics ( full | terse | none | <boolean> );
};
zone <string> [ <class> ] {
type ( slave | secondary );
allow-notify { <address_match_element>; ... };
allow-query { <address_match_element>; ... };
allow-query-on { <address_match_element>; ... };
allow-transfer { <address_match_element>; ... };
allow-update-forwarding { <address_match_element>; ... };
also-notify [ port <integer> ] [ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
alt-transfer-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
alt-transfer-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
auto-dnssec ( allow | maintain | off );
check-names ( fail | warn | ignore );
database <string>;
dialup ( notify | notify-passive | passive | refresh | <boolean> );
dlz <string>;
dnskey-sig-validity <integer>;
dnssec-dnskey-kskonly <boolean>;
dnssec-loadkeys-interval <integer>;
dnssec-policy <string>;
dnssec-update-mode ( maintain | no-resign );
file <quoted_string>;
forward ( first | only );
forwarders [ port <integer> ] [ dscp <integer> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ dscp <integer> ]; ... };
inline-signing <boolean>;
ixfr-from-differences <boolean>;
journal <quoted_string>;
key-directory <quoted_string>;
masterfile-format ( map | raw | text );
masterfile-style ( full | relative );
masters [ port <integer> ] [ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
max-ixfr-ratio ( unlimited | <percentage> );
max-journal-size ( default | unlimited | <sizeval> );
max-records <integer>;
max-refresh-time <integer>;
max-retry-time <integer>;
max-transfer-idle-in <integer>;
max-transfer-idle-out <integer>;
max-transfer-time-in <integer>;
max-transfer-time-out <integer>;
min-refresh-time <integer>;
min-retry-time <integer>;
multi-master <boolean>;
notify ( explicit | master-only | primary-only | <boolean> );
notify-delay <integer>;
notify-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
notify-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
notify-to-soa <boolean>;
primaries [ port <integer> ] [ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
request-expire <boolean>;
request-ixfr <boolean>;
sig-signing-nodes <integer>;
sig-signing-signatures <integer>;
sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ];
transfer-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
transfer-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
try-tcp-refresh <boolean>;
update-check-ksk <boolean>;
use-alt-transfer-source <boolean>;
zero-no-soa-ttl <boolean>;
zone-statistics ( full | terse | none | <boolean> );
};
zone <string> [ <class> ] {
type mirror;
allow-notify { <address_match_element>; ... };
allow-query { <address_match_element>; ... };
allow-query-on { <address_match_element>; ... };
allow-transfer { <address_match_element>; ... };
allow-update-forwarding { <address_match_element>; ... };
also-notify [ port <integer> ] [ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
alt-transfer-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
alt-transfer-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
check-names ( fail | warn | ignore );
database <string>;
file <quoted_string>;
ixfr-from-differences <boolean>;
journal <quoted_string>;
masterfile-format ( map | raw | text );
masterfile-style ( full | relative );
masters [ port <integer> ] [ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
max-ixfr-ratio ( unlimited | <percentage> );
max-journal-size ( default | unlimited | <sizeval> );
max-records <integer>;
max-refresh-time <integer>;
max-retry-time <integer>;
max-transfer-idle-in <integer>;
max-transfer-idle-out <integer>;
max-transfer-time-in <integer>;
max-transfer-time-out <integer>;
min-refresh-time <integer>;
min-retry-time <integer>;
multi-master <boolean>;
notify ( explicit | master-only | primary-only | <boolean> );
notify-delay <integer>;
notify-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
notify-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
primaries [ port <integer> ] [ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
request-expire <boolean>;
request-ixfr <boolean>;
transfer-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
transfer-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
try-tcp-refresh <boolean>;
use-alt-transfer-source <boolean>;
zero-no-soa-ttl <boolean>;
zone-statistics ( full | terse | none | <boolean> );
};
zone <string> [ <class> ] {
type hint;
check-names ( fail | warn | ignore );
delegation-only <boolean>;
file <quoted_string>;
};
zone <string> [ <class> ] {
type stub;
allow-query { <address_match_element>; ... };
allow-query-on { <address_match_element>; ... };
check-names ( fail | warn | ignore );
database <string>;
delegation-only <boolean>;
dialup ( notify | notify-passive | passive | refresh | <boolean> );
file <quoted_string>;
forward ( first | only );
forwarders [ port <integer> ] [ dscp <integer> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ dscp <integer> ]; ... };
masterfile-format ( map | raw | text );
masterfile-style ( full | relative );
masters [ port <integer> ] [ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
max-records <integer>;
max-refresh-time <integer>;
max-retry-time <integer>;
max-transfer-idle-in <integer>;
max-transfer-time-in <integer>;
min-refresh-time <integer>;
min-retry-time <integer>;
multi-master <boolean>;
primaries [ port <integer> ] [ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
transfer-source ( <ipv4_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
transfer-source-v6 ( <ipv6_address> | * ) [ port ( <integer> | * ) ] [ dscp <integer> ];
use-alt-transfer-source <boolean>;
zone-statistics ( full | terse | none | <boolean> );
};
zone <string> [ <class> ] {
type static-stub;
allow-query { <address_match_element>; ... };
allow-query-on { <address_match_element>; ... };
forward ( first | only );
forwarders [ port <integer> ] [ dscp <integer> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ dscp <integer> ]; ... };
max-records <integer>;
server-addresses { ( <ipv4_address> | <ipv6_address> ); ... };
server-names { <string>; ... };
zone-statistics ( full | terse | none | <boolean> );
};
zone <string> [ <class> ] {
type forward;
delegation-only <boolean>;
forward ( first | only );
forwarders [ port <integer> ] [ dscp <integer> ] { ( <ipv4_address> | <ipv6_address> ) [ port <integer> ] [ dscp <integer> ]; ... };
};
zone <string> [ <class> ] {
type redirect;
allow-query { <address_match_element>; ... };
allow-query-on { <address_match_element>; ... };
dlz <string>;
file <quoted_string>;
masterfile-format ( map | raw | text );
masterfile-style ( full | relative );
masters [ port <integer> ] [ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
max-records <integer>;
max-zone-ttl ( unlimited | <duration> );
primaries [ port <integer> ] [ dscp <integer> ] { ( <primaries> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };
zone-statistics ( full | terse | none | <boolean> );
};
zone <string> [ <class> ] {
type delegation-only;
};
zone <string> [ <class> ] {
in-view <string>;
};
4.2.34. zone Statement Definition and Usage¶
4.2.34.1. Zone Types¶
The type keyword is required for the zone configuration unless
it is an in-view configuration. Its acceptable values are:
primary (or master), secondary (or slave), mirror,
hint, stub, static-stub, forward, redirect,
or delegation-only.
primaryA primary zone has a master copy of the data for the zone and is able to provide authoritative answers for it. Type
masteris a synonym forprimary.secondaryA secondary zone is a replica of a primary zone. Type
slaveis a synonym forsecondary. Theprimarieslist specifies one or more IP addresses of primary servers that the secondary contacts to update its copy of the zone. Primaries list elements can also be names of other primaries 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 primary can also be done with per-server TSIG keys. If a file is specified, then the replica is 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 secondary server for the zoneexample.commight place the zone contents into a file calledex/example.com, whereex/is just the first two letters of the zone name. (Most operating systems behave very slowly if there are 100000 files in a single directory.)mirrorA mirror zone is similar to a zone of type
secondary, except its data is subject to DNSSEC validation before being used in answers. Validation is applied to the entire zone during the zone transfer process, and again when the zone file is loaded from disk upon restartingnamed. If validation of a new version of a mirror zone fails, a retransfer is scheduled and the most recent correctly validated version of that zone is used, until it either expires or a newer version validates correctly. If no usable zone data is available for a mirror zone, either due to transfer failure or expiration, traditional DNS recursion is used to look up the answers instead. Mirror zones cannot be used in a view that does not have recursion enabled.Answers coming from a mirror zone look almost exactly like answers from a zone of type
secondary, with the notable exceptions that the AA bit (“authoritative answer”) is not set, and the AD bit (“authenticated data”) is.Mirror zones are intended to be used to set up a fast local copy of the root zone, similar to the one described in RFC 7706. A default list of primary servers for the IANA root zone is built into
namedand thus its mirroring can be enabled using the following configuration:zone "." { type mirror; };
Mirroring a zone other than root requires an explicit list of primary servers to be provided using the
primariesoption (see primaries Statement Grammar for details), and a key-signing key (KSK) for the specified zone to be explicitly configured as a trust anchor.To make mirror zone contents persist between
namedrestarts, use the file option.When configuring NOTIFY for a mirror zone, only
notify no;andnotify explicit;can be used at the zone level; any othernotifysetting at the zone level is a configuration error. Using any othernotifysetting at theoptionsorviewlevel causes that setting to be overridden withnotify explicit;for the mirror zone. The global default for thenotifyoption isyes, so mirror zones are by default configured withnotify explicit;.Outgoing transfers of mirror zones are disabled by default but may be enabled using allow-transfer.
Note
Use of this zone type with any zone other than the root should be considered experimental and may cause performance issues, especially for zones which are large and/or frequently updated.
hintThe initial set of root name servers is specified using a hint zone. When the server starts, 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 default hints.
stubA stub zone is similar to a secondary zone, except that it replicates only the NS records of a primary 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 a glue NS record in a parent zone, at the expense of maintaining a stub zone entry and a set of name server addresses in
named.conf. This usage is not recommended for new configurations, and BIND 9 supports it only in a limited way. If a BIND 9 primary, serving a parent zone, has child stub zones configured, all the secondary servers for the parent zone also need to have the same child stub zones configured.Stub zones can also be used as a way to force the resolution of a given domain to use a particular set of authoritative servers. For example, the caching name servers on a private network using RFC 1918 addressing may be configured with stub zones for
10.in-addr.arpato use a set of internal name servers as the authoritative servers for that domain.static-stubA static-stub zone is similar to a stub zone, with the following exceptions: the zone data is statically configured, rather than transferred from a primary server; and when recursion is necessary for a query that matches a static-stub zone, the locally configured data (name server names and glue addresses) is always used, even if different authoritative information is cached.
Zone data is configured via the
server-addressesandserver-nameszone options.The zone data is maintained in the form of NS and (if necessary) glue A or AAAA RRs internally, which can be seen by dumping zone databases with
rndc dumpdb -all. The configured RRs are considered local configuration parameters rather than public data. Non-recursive queries (i.e., those with the RD bit off) to a static-stub zone are therefore prohibited and are responded to with REFUSED.Since the data is statically configured, no zone maintenance action takes place for a static-stub zone. For example, there is no periodic refresh attempt, and an incoming notify message is rejected with an rcode of NOTAUTH.
Each static-stub zone is configured with internally generated NS and (if necessary) glue A or AAAA RRs.
forwardA forward zone is a way to configure forwarding on a per-domain basis. A
zonestatement of typeforwardcan contain aforwardand/orforwardersstatement, which applies to queries within the domain given by the zone name. If noforwardersstatement is present, or an empty list forforwardersis given, then no forwarding is done for the domain, canceling the effects of any forwarders in theoptionsstatement. Thus, to use this type of zone to change the behavior of the globalforwardoption (that is, “forward first” to, then “forward only”, or vice versa), but use the same servers as set globally, re-specify the global forwarders.redirectRedirect zones are used to provide answers to queries when normal resolution would result in NXDOMAIN being returned. Only one redirect zone is supported per view.
allow-querycan be used to restrict which clients see these answers.If the client has requested DNSSEC records (DO=1) and the NXDOMAIN response is signed, no substitution occurs.
To redirect all NXDOMAIN responses to 100.100.100.2 and 2001:ffff:ffff::100.100.100.2, configure a type
redirectzone named “.”, with the zone file containing wildcard records that point to the desired addresses:*. IN A 100.100.100.2and*. IN AAAA 2001:ffff:ffff::100.100.100.2.As another example, to redirect all Spanish names (under .ES), use similar entries but with the names
*.ES.instead of*.. To redirect all commercial Spanish names (under COM.ES), use wildcard entries called*.COM.ES..Note that the redirect zone supports all possible types; it is not limited to A and AAAA records.
If a redirect zone is configured with a
primariesoption, then it is transferred in as if it were a secondary zone. Otherwise, it is loaded from a file as if it were a primary zone.Because redirect zones are not referenced directly by name, they are not kept in the zone lookup table with normal primary and secondary zones. To reload a redirect zone, use
rndc reload -redirect; to retransfer a redirect zone configured as a secondary, userndc retransfer -redirect. When usingrndc reloadwithout specifying a zone name, redirect zones are reloaded along with other zones.delegation-onlyThis zone type 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 is treated as NXDOMAIN. This does not apply to the zone apex, and should not be applied to leaf zones.
delegation-onlyhas no effect on answers received from forwarders.See caveats in root-delegation-only.
in-viewWhen using multiple views, a
primaryorsecondaryzone configured in one view can be referenced in a subsequent view. This allows both views to use the same zone without the overhead of loading it more than once. This is configured using azonestatement, with anin-viewoption specifying the view in which the zone is defined. Azonestatement containingin-viewdoes not need to specify a type, since that is part of the zone definition in the other view.See Multiple Views for more information.
4.2.34.2. Class¶
The zone’s name may optionally be followed by a class. If a class is not
specified, class IN (for Internet) is assumed. This is correct
for the vast majority of cases.
The hesiod class is named for an information service from MIT’s
Project Athena. It was 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.
4.2.34.3. Zone Options¶
allow-notifySee the description of
allow-notifyin Access Control.allow-querySee the description of
allow-queryin Access Control.allow-query-onSee the description of
allow-query-onin Access Control.allow-transferSee the description of
allow-transferin Access Control.allow-updateSee the description of
allow-updatein Access Control.update-policyThis specifies a “Simple Secure Update” policy. See Dynamic Update Policies.
allow-update-forwardingSee the description of
allow-update-forwardingin Access Control.also-notifyThis option is only meaningful if
notifyis active for this zone. The set of machines that receive aDNS NOTIFYmessage for this zone is made up of all the listed name servers (other than the primary) for the zone, plus any IP addresses specified withalso-notify. A port may be specified with eachalso-notifyaddress to send the notify messages to a port other than the default of 53. A TSIG key may also be specified to cause theNOTIFYto be signed by the given key.also-notifyis not meaningful for stub zones. The default is the empty list.check-namesThis option is used to restrict the character set and syntax of certain domain names in primary files and/or DNS responses received from the network. The default varies according to zone type. For
primaryzones the default isfail; forsecondaryzones the default iswarn. It is not implemented forhintzones.check-mxSee the description of
check-mxin Boolean Options.check-spfSee the description of
check-spfin Boolean Options.check-wildcardSee the description of
check-wildcardin Boolean Options.check-integritySee the description of
check-integrityin Boolean Options.check-siblingSee the description of
check-siblingin Boolean Options.zero-no-soa-ttlSee the description of
zero-no-soa-ttlin Boolean Options.update-check-kskSee the description of
update-check-kskin Boolean Options.dnssec-loadkeys-intervalSee the description of
dnssec-loadkeys-intervalin options Statement Definition and Usage.dnssec-update-modeSee the description of
dnssec-update-modein options Statement Definition and Usage.dnssec-dnskey-kskonlySee the description of
dnssec-dnskey-kskonlyin Boolean Options.try-tcp-refreshSee the description of
try-tcp-refreshin Boolean Options.databaseThis specifies the type of database to be used to store the zone data. The string following the
databasekeyword 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.
dialupSee the description of
dialupin Boolean Options.delegation-onlyThis flag only applies to forward, hint, and stub zones. If set to
yes, then the zone is treated as if it is also a delegation-only type zone.See caveats in root-delegation-only.
fileThis sets the zone’s filename. In
primary,hint, andredirectzones which do not haveprimariesdefined, zone data is loaded from this file. Insecondary,mirror,stub, andredirectzones which do haveprimariesdefined, zone data is retrieved from another server and saved in this file. This option is not applicable to other zone types.forwardThis option is only meaningful if the zone has a forwarders list. The
onlyvalue causes the lookup to fail after trying the forwarders and getting no answer, whilefirstallows a normal lookup to be tried.forwardersThis is 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.journalThis allows the default journal’s filename to be overridden. The default is the zone’s filename with “
.jnl” appended. This is applicable toprimaryandsecondaryzones.max-ixfr-ratioSee the description of
max-ixfr-ratioin options Statement Definition and Usage.max-journal-sizeSee the description of
max-journal-sizein Server Resource Limits.max-recordsSee the description of
max-recordsin Server Resource Limits.max-transfer-time-inSee the description of
max-transfer-time-inin Zone Transfers.max-transfer-idle-inSee the description of
max-transfer-idle-inin Zone Transfers.max-transfer-time-outSee the description of
max-transfer-time-outin Zone Transfers.max-transfer-idle-outSee the description of
max-transfer-idle-outin Zone Transfers.notifySee the description of
notifyin Boolean Options.notify-delaySee the description of
notify-delayin Tuning.notify-to-soaSee the description of
notify-to-soain Boolean Options.zone-statisticsSee the description of
zone-statisticsin options Statement Definition and Usage.server-addressesThis option is only meaningful for static-stub zones. This is a list of IP addresses to which queries should be sent in recursive resolution for the zone. A non-empty list for this option internally configures the apex NS RR with associated glue A or AAAA RRs.
For example, if “example.com” is configured as a static-stub zone with 192.0.2.1 and 2001:db8::1234 in a
server-addressesoption, the following RRs are internally configured:example.com. NS example.com. example.com. A 192.0.2.1 example.com. AAAA 2001:db8::1234
These records are used internally to resolve names under the static-stub zone. For instance, if the server receives a query for “www.example.com” with the RD bit on, the server initiates recursive resolution and sends queries to 192.0.2.1 and/or 2001:db8::1234.
server-namesThis option is only meaningful for static-stub zones. This is a list of domain names of name servers that act as authoritative servers of the static-stub zone. These names are resolved to IP addresses when
namedneeds to send queries to these servers. For this supplemental resolution to be successful, these names must not be a subdomain of the origin name of the static-stub zone. That is, when “example.net” is the origin of a static-stub zone, “ns.example” and “master.example.com” can be specified in theserver-namesoption, but “ns.example.net” cannot; it is rejected by the configuration parser.A non-empty list for this option internally configures the apex NS RR with the specified names. For example, if “example.com” is configured as a static-stub zone with “ns1.example.net” and “ns2.example.net” in a
server-namesoption, the following RRs are internally configured:example.com. NS ns1.example.net. example.com. NS ns2.example.net.
These records are used internally to resolve names under the static-stub zone. For instance, if the server receives a query for “www.example.com” with the RD bit on, the server initiates recursive resolution, resolves “ns1.example.net” and/or “ns2.example.net” to IP addresses, and then sends queries to one or more of these addresses.
sig-validity-intervalSee the description of
sig-validity-intervalin Tuning.sig-signing-nodesSee the description of
sig-signing-nodesin Tuning.sig-signing-signaturesSee the description of
sig-signing-signaturesin Tuning.sig-signing-typeSee the description of
sig-signing-typein Tuning.transfer-sourceSee the description of
transfer-sourcein Zone Transfers.transfer-source-v6See the description of
transfer-source-v6in Zone Transfers.alt-transfer-sourceSee the description of
alt-transfer-sourcein Zone Transfers.alt-transfer-source-v6See the description of
alt-transfer-source-v6in Zone Transfers.use-alt-transfer-sourceSee the description of
use-alt-transfer-sourcein Zone Transfers.notify-sourceSee the description of
notify-sourcein Zone Transfers.notify-source-v6See the description of
notify-source-v6in Zone Transfers.min-refresh-time;max-refresh-time;min-retry-time;max-retry-timeSee the descriptions in Tuning.
ixfr-from-differencesSee the description of
ixfr-from-differencesin Boolean Options. (Note that theixfr-from-differenceschoices ofprimaryandsecondaryare not available at the zone level.)key-directorySee the description of
key-directoryin options Statement Definition and Usage.auto-dnssecSee the description of
auto-dnssecin options Statement Definition and Usage.serial-update-methodSee the description of
serial-update-methodin options Statement Definition and Usage.inline-signingIf
yes, this enables “bump in the wire” signing of a zone, where an unsigned zone is transferred in or loaded from disk and a signed version of the zone is served with, possibly, a different serial number. This behavior is disabled by default.multi-masterSee the description of
multi-masterin Boolean Options.masterfile-formatSee the description of
masterfile-formatin Tuning.max-zone-ttlSee the description of
max-zone-ttlin options Statement Definition and Usage.dnssec-secure-to-insecureSee the description of
dnssec-secure-to-insecurein Boolean Options.
4.2.34.4. Dynamic Update Policies¶
BIND 9 supports two methods of granting clients the right to
perform dynamic updates to a zone, configured by the allow-update
or update-policy options.
The allow-update clause is a simple access control list. Any client
that matches the ACL is granted permission to update any record in the
zone.
The update-policy clause allows more fine-grained control over which
updates are allowed. It specifies a set of rules, in which each rule
either grants or denies permission for one or more names in the zone to
be updated by one or more identities. Identity is determined by the key
that signed the update request, using either TSIG or SIG(0). In most
cases, update-policy rules only apply to key-based identities. There
is no way to specify update permissions based on the client source address.
update-policy rules are only meaningful for zones of type
primary, and are not allowed in any other zone type. It is a
configuration error to specify both allow-update and
update-policy at the same time.
A pre-defined update-policy rule can be switched on with the command
update-policy local;. named automatically
generates a TSIG session key when starting and stores it in a file;
this key can then be used by local clients to update the zone while
named is running. By default, the session key is stored in the file
/var/run/named/session.key, the key name is “local-ddns”, and the
key algorithm is HMAC-SHA256. These values are configurable with the
session-keyfile, session-keyname, and session-keyalg options,
respectively. A client running on the local system, if run with
appropriate permissions, may read the session key from the key file and
use it to sign update requests. The zone’s update policy is set to
allow that key to change any record within the zone. Assuming the key
name is “local-ddns”, this policy is equivalent to:
update-policy { grant local-ddns zonesub any; };
with the additional restriction that only clients connecting from the local system are permitted to send updates.
Note that only one session key is generated by named; all zones
configured to use update-policy local accept the same key.
The command nsupdate -l implements this feature, sending requests to
localhost and signing them using the key retrieved from the session key
file.
Other rule definitions look like this:
( grant | deny ) identity ruletype name types
Each rule grants or denies privileges. Rules are checked in the order in
which they are specified in the update-policy statement. Once a
message has successfully matched a rule, the operation is immediately
granted or denied, and no further rules are examined. There are 16 types
of rules; the rule type is specified by the ruletype field, and the
interpretation of other fields varies depending on the rule type.
In general, a rule is matched when the key that signed an update request
matches the identity field, the name of the record to be updated
matches the name field (in the manner specified by the ruletype
field), and the type of the record to be updated matches the types
field. Details for each rule type are described below.
The identity field must be set to a fully qualified domain name. In
most cases, this represents the name of the TSIG or SIG(0) key that
must be used to sign the update request. If the specified name is a
wildcard, it is subject to DNS wildcard expansion, and the rule may
apply to multiple identities. When a TKEY exchange has been used to
create a shared secret, the identity of the key used to authenticate the
TKEY exchange is used as the identity of the shared secret. Some
rule types use identities matching the client’s Kerberos principal (e.g,
"host/machine@REALM") or Windows realm (machine$@REALM).
The name field also specifies a fully qualified domain name. This often
represents the name of the record to be updated. Interpretation of this
field is dependent on rule type.
If no types are explicitly specified, then a rule matches all types
except RRSIG, NS, SOA, NSEC, and NSEC3. Types may be specified by name,
including ANY; ANY matches all types except NSEC and NSEC3, 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.
If the type is immediately followed by a number in parentheses,
that number is the maximum number of records of that type permitted
to exist in the RRset after an update has been applied. For example,
PTR(1) indicates that only one PTR record is allowed. If an
attempt is made to add two PTR records in an update, the second one
is silently discarded. If a PTR record already exists, both
new records are silently discarded.
If type ANY is specified with a limit, then that limit applies to
all types that are not otherwise specified. For example, A PTR(1)
ANY(2) indicates that an unlimited number of A records can exist,
but only one PTR record, and no more than two of any other type.
Typical use with a rule grant * tcp-self . PTR(1); in the zone
2.0.192.IN-ADDR.ARPA looks like this:
nsupdate -v <<EOF
local 192.0.2.1
del 1.2.0.192.IN-ADDR.ARPA PTR
add 1.2.0.192.IN-ADDR.ARPA 0 PTR EXAMPLE.COM
send
EOF
The ruletype field has 16 values: name, subdomain, zonesub, wildcard,
self, selfsub, selfwild, ms-self, ms-selfsub, ms-subdomain,
krb5-self, krb5-selfsub, krb5-subdomain,
tcp-self, 6to4-self, and external.
nameWith exact-match semantics, this rule matches when the name being updated is identical to the contents of the
namefield.subdomainThis rule matches when the name being updated is a subdomain of, or identical to, the contents of the
namefield.zonesubThis rule is similar to subdomain, except that it matches when the name being updated is a subdomain of the zone in which the
update-policystatement appears. This obviates the need to type the zone name twice, and enables the use of a standardupdate-policystatement in multiple zones without modification. When this rule is used, thenamefield is omitted.wildcardThe
namefield is subject to DNS wildcard expansion, and this rule matches when the name being updated is a valid expansion of the wildcard.selfThis rule matches when the name of the record being updated matches the contents of the
identityfield. Thenamefield is ignored. To avoid confusion, it is recommended that this field be set to the same value as theidentityfield or to “.” Theselfrule type is most useful when allowing one key per name to update, where the key has the same name as the record to be updated. In this case, theidentityfield can be specified as*(asterisk).selfsubThis rule is similar to
self, except that subdomains ofselfcan also be updated.selfwildThis rule is similar to
self, except that only subdomains ofselfcan be updated.ms-selfWhen a client sends an UPDATE using a Windows machine principal (for example,
machine$@REALM), this rule allows records with the absolute name ofmachine.REALMto be updated.The realm to be matched is specified in the
identityfield.The
namefield has no effect on this rule; it should be set to “.” as a placeholder.For example,
grant EXAMPLE.COM ms-self . A AAAAallows any machine with a valid principal in the realmEXAMPLE.COMto update its own address records.ms-selfsubThis is similar to
ms-self, except it also allows updates to any subdomain of the name specified in the Windows machine principal, not just to the name itself.ms-subdomainWhen a client sends an UPDATE using a Windows machine principal (for example,
machine$@REALM), this rule allows any machine in the specified realm to update any record in the zone or in a specified subdomain of the zone.The realm to be matched is specified in the
identityfield.The
namefield specifies the subdomain that may be updated. If set to “.” or any other name at or above the zone apex, any name in the zone can be updated.For example, if
update-policyfor the zone “example.com” includesgrant EXAMPLE.COM ms-subdomain hosts.example.com. AA AAAA, any machine with a valid principal in the realmEXAMPLE.COMis able to update address records at or belowhosts.example.com.krb5-selfWhen a client sends an UPDATE using a Kerberos machine principal (for example,
host/machine@REALM), this rule allows records with the absolute name ofmachineto be updated, provided it has been authenticated by REALM. This is similar but not identical toms-self, due to themachinepart of the Kerberos principal being an absolute name instead of an unqualified name.The realm to be matched is specified in the
identityfield.The
namefield has no effect on this rule; it should be set to “.” as a placeholder.For example,
grant EXAMPLE.COM krb5-self . A AAAAallows any machine with a valid principal in the realmEXAMPLE.COMto update its own address records.krb5-selfsubThis is similar to
krb5-self, except it also allows updates to any subdomain of the name specified in themachinepart of the Kerberos principal, not just to the name itself.krb5-subdomainThis rule is identical to
ms-subdomain, except that it works with Kerberos machine principals (i.e.,host/machine@REALM) rather than Windows machine principals.tcp-selfThis rule allows updates that have been sent via TCP and for which the standard mapping from the client’s IP address into the
in-addr.arpaandip6.arpanamespaces matches the name to be updated. Theidentityfield must match that name. Thenamefield should be set to “.”. Note that, since identity is based on the client’s IP address, it is not necessary for update request messages to be signed.Note
It is theoretically possible to spoof these TCP sessions.
6to4-selfThis allows the name matching a 6to4 IPv6 prefix, as specified in RFC 3056, to be updated by any TCP connection from either the 6to4 network or from the corresponding IPv4 address. This is intended to allow NS or DNAME RRsets to be added to the
ip6.arpareverse tree.The
identityfield must match the 6to4 prefix inip6.arpa. Thenamefield should be set to “.”. Note that, since identity is based on the client’s IP address, it is not necessary for update request messages to be signed.In addition, if specified for an
ip6.arpaname outside of the2.0.0.2.ip6.arpanamespace, the corresponding /48 reverse name can be updated. For example, TCP/IPv6 connections from 2001:DB8:ED0C::/48 can update records atC.0.D.E.8.B.D.0.1.0.0.2.ip6.arpa.Note
It is theoretically possible to spoof these TCP sessions.
externalThis rule allows
namedto defer the decision of whether to allow a given update to an external daemon.The method of communicating with the daemon is specified in the
identityfield, the format of which is “local:path”, where “path” is the location of a Unix-domain socket. (Currently, “local” is the only supported mechanism.)Requests to the external daemon are sent over the Unix-domain socket as datagrams with the following format:
Protocol version number (4 bytes, network byte order, currently 1) Request length (4 bytes, network byte order) Signer (null-terminated string) Name (null-terminated string) TCP source address (null-terminated string) Rdata type (null-terminated string) Key (null-terminated string) TKEY token length (4 bytes, network byte order) TKEY token (remainder of packet)
The daemon replies with a four-byte value in network byte order, containing either 0 or 1; 0 indicates that the specified update is not permitted, and 1 indicates that it is.
4.2.34.5. Multiple Views¶
When multiple views are in use, a zone may be referenced by more than
one of them. Often, the views contain different zones with the same
name, allowing different clients to receive different answers for the
same queries. At times, however, it is desirable for multiple views to
contain identical zones. The in-view zone option provides an
efficient way to do this; it allows a view to reference a zone that was
defined in a previously configured view. For example:
view internal {
match-clients { 10/8; };
zone example.com {
type primary;
file "example-external.db";
};
};
view external {
match-clients { any; };
zone example.com {
in-view internal;
};
};
An in-view option cannot refer to a view that is configured later in
the configuration file.
A zone statement which uses the in-view option may not use any
other options, with the exception of forward and forwarders.
(These options control the behavior of the containing view, rather than
change the zone object itself.)
Zone-level ACLs (e.g., allow-query, allow-transfer), and other configuration details of the zone, are all set in the view the referenced zone is defined in. Be careful to ensure that ACLs are wide enough for all views referencing the zone.
An in-view zone cannot be used as a response policy zone.
An in-view zone is not intended to reference a forward zone.
4.3. Zone File¶
4.3.1. Types of Resource Records and When to Use Them¶
This section, largely borrowed from RFC 1034, describes the concept of a Resource Record (RR) and explains when each type is used. Since the publication of RFC 1034, several new RRs have been identified and implemented in the DNS. These are also included.
4.3.1.1. Resource Records¶
A domain name identifies a node. Each node has a set of resource information, which may be empty. The set of resource information associated with a particular name is composed of separate RRs. The order of RRs in a set is not significant and need not be preserved by name servers, resolvers, or other parts of the DNS. However, sorting of multiple RRs is permitted for optimization purposes: for example, to specify that a particular nearby server be tried first. See The sortlist Statement and 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 an instance of a protocol.
- RDATA
The resource data. The format of the data is type- and sometimes class-specific.
For a complete list of types of valid RRs, including those that have been obsoleted, please refer to https://en.wikipedia.org/wiki/List_of_DNS_record_types.
The following classes of resource records are currently valid in the DNS:
- IN
The Internet.
- CH
Chaosnet, a LAN protocol created at MIT in the mid-1970s. It was rarely used for its historical purpose, but was reused for BIND’s built-in server information zones, e.g.,
version.bind.- HS
Hesiod, an information service developed by MIT’s Project Athena. It was used to share information about various systems databases, such as users, groups, printers, etc.
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 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; that also times out, but follows 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 is anticipated, the TTL can be reduced prior to the change to minimize inconsistency, 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.
4.3.1.2. Textual Expression of RRs¶
RRs are represented in binary form in the packets of the DNS protocol, and are usually represented in highly encoded form when stored in a name server or resolver. In the examples provided in RFC 1034, a style similar to that used in primary 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 are listed 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. 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 interest of clarity.
The resource data or RDATA section of the RR is given using knowledge of the typical representation for the data.
For example, the RRs carried in a message might be shown as:
ISI.EDU.
MX
10 VENERA.ISI.EDU.
MX
10 VAXA.ISI.EDU
VENERA.ISI.EDU
A
128.9.0.32
A
10.1.0.52
VAXA.ISI.EDU
A
10.2.0.27
A
128.9.0.33
The MX RRs have an RDATA section which consists of a 16-bit number followed by a domain name. The address RRs use a standard IP address format to contain a 32-bit Internet address.
The above example shows six RRs, with two RRs at each of three domain names.
Here is another possible example:
XX.LCS.MIT.EDU.
IN A
10.0.0.44
CH A
MIT.EDU. 2420
This shows two addresses for XX.LCS.MIT.EDU, each of a
different class.
4.3.2. Discussion of MX Records¶
As described above, domain servers store information as a series of resource records, each of which contains a particular piece of information about a given domain name (which is usually, but not always, a host). The simplest way to think of an 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 falls 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 is 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 is ignored. Instead, the mail is delivered to the server specified in the MX record pointed to by the CNAME. For example:
example.com.
IN
MX
10
mail.example.com.
IN
MX
10
mail2.example.com.
IN
MX
20
mail.backup.org.
mail.example.com.
IN
A
10.0.0.1
mail2.example.com.
IN
A
10.0.0.2
Mail delivery is attempted to mail.example.com and
mail2.example.com (in any order); if neither of those succeeds,
delivery to mail.backup.org is attempted.
4.3.3. Setting TTLs¶
The time-to-live (TTL) 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 an RR can be cached before it should be discarded. The following three types of TTLs are currently used in a zone file.
- SOA
The last field in the SOA is the negative caching TTL. This controls how long other servers cache no-such-domain (NXDOMAIN) responses from this server.
The maximum time for negative caching is 3 hours (3h).
- $TTL
The $TTL directive at the top of the zone file (before the SOA) gives a default TTL for every RR without a specific TTL set.
- RR TTLs
Each RR can have a TTL as the second field in the RR, which controls how long other servers can cache it.
All of these TTLs default to units of seconds, though units can be
explicitly specified: for example, 1h30m.
4.3.4. Inverse Mapping in IPv4¶
Reverse name resolution (that is, translation from IP address to name)
is achieved by means of the in-addr.arpa domain and PTR records.
Entries in the in-addr.arpa domain are made in least-to-most significant
order, read left to right. This is the opposite order to the way IP
addresses are usually written. Thus, a machine with an IP address of
10.1.2.3 would have a corresponding in-addr.arpa name of
3.2.1.10.in-addr.arpa. This name should have a PTR resource record whose
data field is the name of the machine or, optionally, multiple PTR
records if the machine has more than one name. For example, in the
example.com domain:
$ORIGIN
2.1.10.in-addr.arpa
3
IN PTR foo.example.com.
Note
The $ORIGIN line in this example is only to provide context;
it does not necessarily appear in the actual
usage. It is only used here to indicate that the example is
relative to the listed origin.
4.3.5. Other Zone File Directives¶
The DNS “master file” format was initially defined in RFC 1035 and has subsequently been extended. While the format itself is class-independent, all records in a zone file must be of the same class.
Master file directives include $ORIGIN, $INCLUDE, and $TTL.
4.3.5.1. The @ (at-sign)¶
When used in the label (or name) field, the asperand or at-sign (@)
symbol represents the current origin. At the start of the zone file, it
is the <zone_name>, followed by a trailing dot (.).
4.3.5.2. The $ORIGIN Directive¶
Syntax: $ORIGIN domain-name [comment]
$ORIGIN sets the domain name that is appended to any
unqualified records. When a zone is first read, there is an implicit
$ORIGIN <zone_name>``.``; note the trailing dot. 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.
4.3.5.3. The $INCLUDE Directive¶
Syntax: $INCLUDE filename [origin] [comment]
This reads and processes the file filename as if it were included in 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.
4.3.6. BIND Primary File Extension: the $GENERATE Directive¶
Syntax: $GENERATE range lhs [ttl] [class] type rhs [comment]
$GENERATE is used to create a series of resource records that only
differ from each other by an iterator. $GENERATE can be used to
easily generate the sets of records required to support sub-/24 reverse
delegations described in RFC 2317.
$ORIGIN 0.0.192.IN-ADDR.ARPA.
$GENERATE 1-2 @ NS SERVER$.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.
Both generate a set of A and MX records. Note the MX’s right-hand side is a quoted string. The quotes are stripped when the right-hand side is processed.
$ORIGIN EXAMPLE.
$GENERATE 1-127 HOST-$ A 1.2.3.$
$GENERATE 1-127 HOST-$ MX "0 ."
is equivalent to
HOST-1.EXAMPLE. A 1.2.3.1
HOST-1.EXAMPLE. MX 0 .
HOST-2.EXAMPLE. A 1.2.3.2
HOST-2.EXAMPLE. MX 0 .
HOST-3.EXAMPLE. A 1.2.3.3
HOST-3.EXAMPLE. MX 0 .
...
HOST-127.EXAMPLE. A 1.2.3.127
HOST-127.EXAMPLE. MX 0 .
rangeThis can be one of two forms: start-stop or start-stop/step. If the first form is used, then step is set to 1. “start”, “stop”, and “step” must be positive integers between 0 and (2^31)-1. “start” must not be larger than “stop”.
ownerThis describes the owner name of the resource records to be created. Any single
$(dollar sign) symbols within theownerstring are replaced by the iterator value. To get a$in the output, 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$, as in${offset[,width[,base]]}. For example,${-20,3,d}subtracts 20 from the current value and prints the result as a decimal in a zero-padded field of width 3. Available output forms are decimal (d), octal (o), hexadecimal (xorXfor uppercase), and nibble (norNfor uppercase).The default modifier is
${0,0,d}. If theowneris not absolute, the current$ORIGINis appended to the name.In nibble mode, the value is treated as if it were a reversed hexadecimal string, with each hexadecimal digit as a separate label. The width field includes the label separator.
For compatibility with earlier versions,
$$is still recognized as indicating a literal $ in the output.ttlThis specifies the time-to-live of the generated records. If not specified, this is inherited using the normal TTL inheritance rules.
classandttlcan be entered in either order.classThis specifies the class of the generated records. This must match the zone class if it is specified.
classandttlcan be entered in either order.typeThis can be any valid type.
rdataThis is a string containing the RDATA of the resource record to be created. It may be quoted if there are spaces in the string; the quotation marks do not appear in the generated record.
The $GENERATE directive is a BIND extension and not part of the
standard zone file format.
4.3.7. Additional File Formats¶
In addition to the standard text format, BIND 9 supports the ability to read or dump to zone files in other formats.
The raw format is a binary representation of zone data in a manner
similar to that used in zone transfers. Since it does not require
parsing text, load time is significantly reduced.
An even faster alternative is the map format, which is an image of a
BIND 9 in-memory zone database; it can be loaded directly
into memory via the mmap() function and the zone can begin serving
queries almost immediately.
For a primary server, a zone file in raw or map format is
expected to be generated from a textual zone file by the
named-compilezone command. For a secondary server or a dynamic
zone, the zone file is automatically generated when named dumps the zone contents
after zone transfer or when applying prior updates, if one of these
formats is specified by the masterfile-format option.
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. Make any necessary modifications to the text file, and
then convert it to the binary form via the named-compilezone
command again.
Note that map format is extremely architecture-specific. A map
file cannot be used on a system with different pointer size,
endianness, or data alignment than the system on which it was generated,
and should in general be used only inside a single system. While raw
format uses network byte order and avoids architecture-dependent data
alignment so that it is as portable as possible, it is also primarily
expected to be used inside the same single system. To export a zone file
in either raw or map format, or make a portable backup of such a
file, conversion to text format is recommended.
4.4. BIND 9 Statistics¶
BIND 9 maintains lots of statistics information and provides several interfaces for users to access those statistics. The available statistics include all statistics counters that are meaningful in BIND 9, and other information that is considered useful.
The statistics information is categorized into the following sections:
- Incoming Requests
The number of incoming DNS requests for each OPCODE.
- Incoming Queries
The number of incoming queries for each RR type.
- Outgoing Queries
The number of outgoing queries for each RR type sent from the internal resolver, maintained per view.
- Name Server Statistics
Statistics counters for incoming request processing.
- Zone Maintenance Statistics
Statistics counters regarding zone maintenance operations, such as zone transfers.
- Resolver Statistics
Statistics counters for name resolutions performed in the internal resolver, maintained per view.
- Cache DB RRsets
Statistics counters related to cache contents, maintained per view.
The “NXDOMAIN” counter is the number of names that have been cached as nonexistent. Counters named for RR types indicate the number of active RRsets for each type in the cache database.
If an RR type name is preceded by an exclamation point (!), it represents the number of records in the cache which indicate that the type does not exist for a particular name; this is also known as “NXRRSET”. If an RR type name is preceded by a hash mark (#), it represents the number of RRsets for this type that are present in the cache but whose TTLs have expired; these RRsets may only be used if stale answers are enabled. If an RR type name is preceded by a tilde (~), it represents the number of RRsets for this type that are present in the cache database but are marked for garbage collection; these RRsets cannot be used.
- Socket I/O Statistics
Statistics counters for network-related events.
A subset of Name Server Statistics is collected and shown per zone for
which the server has the authority, when zone-statistics is set to
full (or yes), for backward compatibility. See the description of
zone-statistics in options Statement Definition and Usage for further details.
These statistics counters are shown with their zone and view names. The view name is omitted when the server is not configured with explicit views.
There are currently two user interfaces to get access to the statistics.
One is in plain-text format, dumped to the file specified by the
statistics-file configuration option; the other is remotely
accessible via a statistics channel when the statistics-channels
statement is specified in the configuration file (see statistics-channels Statement Grammar.)
4.4.1. The Statistics File¶
The text format statistics dump begins with a line, like:
+++ Statistics Dump +++ (973798949)
The number in parentheses is a standard Unix-style timestamp, measured in seconds since January 1, 1970. Following that line is a set of statistics information, which is categorized as described above. Each section begins with a line, like:
++ Name Server Statistics ++
Each section consists of lines, each containing the statistics counter value followed by its textual description; see below for available counters. For brevity, counters that have a value of 0 are not shown in the statistics file.
The statistics dump ends with the line where the number is identical to the number in the beginning line; for example:
--- Statistics Dump --- (973798949)
4.4.2. Statistics Counters¶
The following lists summarize the statistics counters that BIND 9 provides. For each counter, the abbreviated symbol name is given; these symbols are shown in the statistics information accessed via an HTTP statistics channel. The description of the counter is also shown in the statistics file but, in this document, may be slightly modified for better readability.
4.4.2.1. Name Server Statistics Counters¶
Requestv4This indicates the number of IPv4 requests received. Note: this also counts non-query requests.
Requestv6This indicates the number of IPv6 requests received. Note: this also counts non-query requests.
ReqEdns0This indicates the number of requests received with EDNS(0).
ReqBadEDN SVerThis indicates the number of requests received with an unsupported EDNS version.
ReqTSIGThis indicates the number of requests received with TSIG.
ReqSIG0This indicates the number of requests received with SIG(0).
ReqBadSIGThis indicates the number of requests received with an invalid (TSIG or SIG(0)) signature.
ReqTCPThis indicates the number of TCP requests received.
AuthQryRejThis indicates the number of rejected authoritative (non-recursive) queries.
RecQryRejThis indicates the number of rejected recursive queries.
XfrRejThis indicates the number of rejected zone transfer requests.
UpdateRejThis indicates the number of rejected dynamic update requests.
ResponseThis indicates the number of responses sent.
RespTruncatedThis indicates the number of truncated responses sent.
RespEDNS0This indicates the number of responses sent with EDNS(0).
RespTSIGThis indicates the number of responses sent with TSIG.
RespSIG0This indicates the number of responses sent with SIG(0).
QrySuccessThis indicates the number of queries that resulted in a successful answer, meaning queries which return a NOERROR response with at least one answer RR. This corresponds to the
successcounter of previous versions of BIND 9.QryAuthAnsThis indicates the number of queries that resulted in an authoritative answer.
QryNoauthAnsThis indicates the number of queries that resulted in a non-authoritative answer.
QryReferralThis indicates the number of queries that resulted in a referral answer. This corresponds to the
referralcounter of previous versions of BIND 9.QryNxrrsetThis indicates the number of queries that resulted in NOERROR responses with no data. This corresponds to the
nxrrsetcounter of previous versions of BIND 9.QrySERVFAILThis indicates the number of queries that resulted in SERVFAIL.
QryFORMERRThis indicates the number of queries that resulted in FORMERR.
QryNXDOMAINThis indicates the number of queries that resulted in NXDOMAIN. This corresponds to the
nxdomaincounter of previous versions of BIND 9.QryRecursionThis indicates the number of queries that caused the server to perform recursion in order to find the final answer. This corresponds to the
recursioncounter of previous versions of BIND 9.QryDuplicateThis indicates the number of queries which the server attempted to recurse but for which it discovered an existing query with the same IP address, port, query ID, name, type, and class already being processed. This corresponds to the
duplicatecounter of previous versions of BIND 9.QryDroppedThis indicates the number of recursive queries for which the server discovered an excessive number of existing recursive queries for the same name, type, and class, and which were subsequently dropped. This is the number of dropped queries due to the reason explained with the
clients-per-queryandmax-clients-per-queryoptions (see clients-per-query). This corresponds to thedroppedcounter of previous versions of BIND 9.QryFailureThis indicates the number of query failures. This corresponds to the
failurecounter of previous versions of BIND 9. Note: this counter is provided mainly for backward compatibility with previous versions; normally, more fine-grained counters such asAuthQryRejandRecQryRejthat would also fall into this counter are provided, so this counter is not of much interest in practice.QryNXRedirThis indicates the number of queries that resulted in NXDOMAIN that were redirected.
QryNXRedirRLookupThis indicates the number of queries that resulted in NXDOMAIN that were redirected and resulted in a successful remote lookup.
XfrReqDoneThis indicates the number of requested and completed zone transfers.
UpdateReqFwdThis indicates the number of forwarded update requests.
UpdateRespFwdThis indicates the number of forwarded update responses.
UpdateFwdFailThis indicates the number of forwarded dynamic updates that failed.
UpdateDoneThis indicates the number of completed dynamic updates.
UpdateFailThis indicates the number of failed dynamic updates.
UpdateBadPrereqThis indicates the number of dynamic updates rejected due to a prerequisite failure.
RateDroppedThis indicates the number of responses dropped due to rate limits.
RateSlippedThis indicates the number of responses truncated by rate limits.
RPZRewritesThis indicates the number of response policy zone rewrites.
4.4.2.2. Zone Maintenance Statistics Counters¶
NotifyOutv4This indicates the number of IPv4 notifies sent.
NotifyOutv6This indicates the number of IPv6 notifies sent.
NotifyInv4This indicates the number of IPv4 notifies received.
NotifyInv6This indicates the number of IPv6 notifies received.
NotifyRejThis indicates the number of incoming notifies rejected.
SOAOutv4This indicates the number of IPv4 SOA queries sent.
SOAOutv6This indicates the number of IPv6 SOA queries sent.
AXFRReqv4This indicates the number of requested IPv4 AXFRs.
AXFRReqv6This indicates the number of requested IPv6 AXFRs.
IXFRReqv4This indicates the number of requested IPv4 IXFRs.
IXFRReqv6This indicates the number of requested IPv6 IXFRs.
XfrSuccessThis indicates the number of successful zone transfer requests.
XfrFailThis indicates the number of failed zone transfer requests.
4.4.2.3. Resolver Statistics Counters¶
Queryv4This indicates the number of IPv4 queries sent.
Queryv6This indicates the number of IPv6 queries sent.
Responsev4This indicates the number of IPv4 responses received.
Responsev6This indicates the number of IPv6 responses received.
NXDOMAINThis indicates the number of NXDOMAINs received.
SERVFAILThis indicates the number of SERVFAILs received.
FORMERRThis indicates the number of FORMERRs received.
OtherErrorThis indicates the number of other errors received.
EDNS0FailThis indicates the number of EDNS(0) query failures.
MismatchThis indicates the number of mismatched responses received, meaning the DNS ID, response’s source address, and/or the response’s source port does not match what was expected. (The port must be 53 or as defined by the
portoption.) This may be an indication of a cache poisoning attempt.TruncatedThis indicates the number of truncated responses received.
LameThis indicates the number of lame delegations received.
RetryThis indicates the number of query retries performed.
QueryAbortThis indicates the number of queries aborted due to quota control.
QuerySockFailThis indicates the number of failures in opening query sockets. One common reason for such failures is due to a limitation on file descriptors.
QueryTimeoutThis indicates the number of query timeouts.
GlueFetchv4This indicates the number of IPv4 NS address fetches invoked.
GlueFetchv6This indicates the number of IPv6 NS address fetches invoked.
GlueFetchv4FailThis indicates the number of failed IPv4 NS address fetches.
GlueFetchv6FailThis indicates the number of failed IPv6 NS address fetches.
ValAttemptThis indicates the number of attempted DNSSEC validations.
ValOkThis indicates the number of successful DNSSEC validations.
ValNegOkThis indicates the number of successful DNSSEC validations on negative information.
ValFailThis indicates the number of failed DNSSEC validations.
QryRTTnnThis provides a frequency table on query round-trip times (RTTs). Each
nnspecifies the corresponding frequency. In the sequence ofnn_1,nn_2, …,nn_m, the value ofnn_iis the number of queries whose RTTs are betweennn_(i-1)(inclusive) andnn_i(exclusive) milliseconds. For the sake of convenience, we definenn_0to be 0. The last entry should be represented asnn_m+, which means the number of queries whose RTTs are equal to or greater thannn_mmilliseconds.
4.4.2.4. Socket I/O Statistics Counters¶
Socket I/O statistics counters are defined per socket type, which are
UDP4 (UDP/IPv4), UDP6 (UDP/IPv6), TCP4 (TCP/IPv4), TCP6
(TCP/IPv6), Unix (Unix Domain), and FDwatch (sockets opened
outside the socket module). In the following list, <TYPE> represents
a socket type. Not all counters are available for all socket types;
exceptions are noted in the descriptions.
<TYPE>OpenThis indicates the number of sockets opened successfully. This counter does not apply to the
FDwatchtype.<TYPE>OpenFailThis indicates the number of failures to open sockets. This counter does not apply to the
FDwatchtype.<TYPE>CloseThis indicates the number of closed sockets.
<TYPE>BindFailThis indicates the number of failures to bind sockets.
<TYPE>ConnFailThis indicates the number of failures to connect sockets.
<TYPE>ConnThis indicates the number of connections established successfully.
<TYPE>AcceptFailThis indicates the number of failures to accept incoming connection requests. This counter does not apply to the
UDPandFDwatchtypes.<TYPE>AcceptThis indicates the number of incoming connections successfully accepted. This counter does not apply to the
UDPandFDwatchtypes.<TYPE>SendErrThis indicates the number of errors in socket send operations.
<TYPE>RecvErrThis indicates the number of errors in socket receive operations, including errors of send operations on a connected UDP socket, notified by an ICMP error message.