IP-address-based access control for queries, zone transfers, and
updates that may be specified on a zone-by-zone basis
More efficient zone transfers
Improved performance for servers with thousands of zones
The server no longer forks for outbound zone transfers
Many bug fixes
BIND 8 is much more configurable than the previous release
of BIND. There are entirely new areas of configuration, such as
access control lists and categorized logging. Many options that
previously applied to all zones can now be used selectively. These
features, plus a consideration of future configuration needs led
to the creation of a new configuration file format.
The logging statement configures a wide variety of logging
options for the nameserver. Its channel phrase associates output
methods, format options and severity levels with a name that can
then be used with the category phrase to select how various classes
of messages are logged.
Only one logging statement is used to define as many channels
and categories as are wanted. If there are multiple logging statements
in a configuration, the first defined determines the logging, and
warnings are issued for the others. If there is no logging statement,
the logging configuration will be:
All log output goes to one or more "channels"; make as many of them as you want.
Every channel definition must include a clause that says whether messages
selected for the channel go to a file, to a particular syslog facility,
or are discarded. It can optionally also limit the message severity
level that will be accepted by the channel (default is "info"), and whether
to include a named generated time stamp, the category name and/or
severity level (default is not to include any).
The word null as the destination option for the channel will
cause all messages sent to it to be discarded; other options for
the channel are meaningless.
The file clause can include limitations both on how large
the file is allowed to become, and how many versions of the file
will be saved each time the file is opened.
The size option for files is simply a hard ceiling on log growth. If the file
ever exceeds the size, then named will just not write anything more to
it until the file is reopened; exceeding the size does not automatically
trigger a reopen. The default behavior is to not limit the size of the file.
If you use the version logfile option, then named will retain many
backup versions of the file by renaming them when opening. For example, if you
choose to keep 3 old versions of the file "lamers.log" then just
before it is opened lamers.log.1 is renamed to lames.log.2,
lamers.log.0 is renamed to lamers.log.1, and
lamers.log is renamed to lamers.log.0. No rolled versions are
kept by default. The unlimited keyword is synonymous with 99 in current
BIND releases.
The argument for the syslog clause is a syslog facility described earlier in
this manual. How syslog will handle messages sent to this facility is described
under syslog.conf earlier in this manual. If you have a system which
uses a very old version of syslog and that only uses two arguments to the
openlog() function, then this clause is silently ignored.
The severity clause works like syslog's "priorities",
except that they can also be used if you are writing straight to
a file rather than using syslog. Messages which are not at least
of the severity level given will not be selected for the channel;
messages of higher severity levels will be accepted.
If you are using syslog, then the syslog.conf priorities will also
determine what eventually passes through. For example, defining a channel
facility and severity as daemon and debug but only logging
daemon.warning via syslog.conf will cause messages of
severity information and notice to be dropped. If the situation were reversed,
with named writing messages of only warning or higher, then
syslog would print all messages it received from the channel.
The server can supply extensive debugging information when
it is in debugging mode. If the server's global debug level
is greater than zero, then debugging mode will be active. The global
debug level is set either by starting the server with the "-d" flag
followed by a positive integer, or by sending the server the SIGUSR1
signal (for example, by using "ndc trace").
The global debug level can be set to zero, and debugging mode turned
off, by sending the server the SIGUSR2 signal ("ndc notrace".
All debugging messages in the server have a debug level, and higher
debug levels give more detailed output. Channels that specify a
specific debug severity, for example,
will get debugging output of level 3 or less any time the
server is in debugging mode, regardless of the global debugging
level. Channels with dynamic severity use the server's
global level to determine what messages to print.
If print-time has been turned on, then the date and time will be
logged. print-time may be specified for a syslog channel, but is
usually pointless since syslog also prints the date and time. If
print-category is requested, then the category of the message will be
logged as well. Finally, if print-severity is on, then the severity
level of the message will
be logged. The print options may be used in any combination, and will
always be printed in the following order: time, category, and severity.
Here is an example where all three print options are on:
28-Apr-1997 15:05:32.863 default: notice: Ready to answer queries.
There are four predefined channels that are used for named's default
logging as follows. How they are used
is described in the next section, The category phrase.
channel default_syslog {
syslog daemon; # send to syslog's daemon facility
severity info; # only send priority info and higher
};
channel default_debug {
file "named.run";# write to named.run in the working directory
# Note: stderr is used instead of "named.run"
# if the server is started with the "-f" option.
severity dynamic; # log at the server's current debug level
};
channel default_stderr {# writes to stderr
file "<stderr>"; # this is illustrative only; there's currently
# no way of specifying an nternal file
# descriptor in the configuration language.
severity info; # only send priority info and higher
};
channel null {
null; # toss anything sent to this channel
};
Once a channel is defined, it cannot be redefined. Thus you
cannot alter the built-in channels directly, but you can modify
the default logging by pointing categories at channels you have defined.
The Category Phrase
There are many categories, so you can send the logs you want to see wherever
you want, without seeing logs you don't want. If you don't specify a list of
channels for a category, then log messages in that category will be sent to the
default category instead. If you don't specify a default category, the
following "default" is used:
The catch-all. Many things still aren't classified into categories,
and they all end up here. Also, if you don't specify any channels for a
category, the default category is used instead. If you do not define the
default category, the following definition is used:
A short log message is generated for every query the
server receives.
lame-servers
Messages like "Lame server on ..."
statistics
Statistics.
panic
If the server has to shut itself down due to an internal problem, it
will log the problem in this category as well as in the problem's native
category. If you do not define the panic category, the following
definition is used: category panic { default_syslog; default_stderr;
};
update
Dynamic updates.
ncache
Negative caching.
xfer-in
Zone transfers the server is receiving.
xfer-out
Zone transfers the server is sending.
db
All database operations.
eventlib
Debugging info from the event system. Only one channel may be
specified for this category, and it must be a file channel. If you do not
define the eventlib category, the following definition is used:
category eventlib { default_debug; };
packet
Dumps of packets received and sent. Only one channel may be specified
for this category, and it must be a file channel. If you do not define
the packet category, the following definition is used:
category packet { default_debug; };
notify
The NOTIFY protocol.
cname
Messages like "... points to a CNAME".
security
Approved/unapproved requests.
os
Operating system problems.
insist
Internal consistency check failures.
maintenance
Periodic maintenance events.
load
Zone loading messages.
response-checks
Messages arising from response checking, such as "Malformed response
...", "wrong ans. name ...", "unrelated additional info ...", "invalid
RR type ...", and "bad referral ...".
zone "." [ ( in | hs | hesiod | chaos ) ] {
type hint;
file path_name;
[ check-names ( warn | fail | ignore ); ]
};
Definition and Usage (Zone Types)
master
The master copy of the data in a zone.
slave
A slave zone is a replica of a master zone. The masters list specifies
one or more IP addresses that the slave contacts to update its copy of
the zone. If file is specified, then the replica will be written to the
file. Use of file is recommended, since it often speeds server startup
and eliminates a needless waste of bandwidth.
stub
A stub zone is like a slave zone, except that it replicates only the
NS records of a master zone instead of the entire zone.
hint
The initial set of root nameservers is specified using a hint zone.
When the server starts up, it uses the root hints to find a root
nameserver and get the most recent list of root nameservers.
NOTE: Previous releases of BIND used the term primary for a master zone,
secondary for a slave zone, and cache for a hint zone.
Class
The zone's name may optionally be followed by a class.
If a class is not specified, class in is used.
Options
check-names
See Name Checking.
allow-query
See the description of allow-query in the Access Control
section.
allow-update
Specifies which hosts are allowed to submit Dynamic DNS updates to the
server. The default is to deny updates from all hosts.
allow- transfer
See the description of allow-transfer in the Access
Control section.
max-transfer-time-in
See the description of max-transfer-time-in in the Zone
Transfers section.
notify
See the description of notify in the Boolean Options section.
also-notify
also-notify is only meaningful if notify is active for this
zone.
The set of machines that will receive a DNS NOTIFY message for this zone
is made up of all the listed nameservers for the zone (other than the
primary master) plus any IP addresses specified with
also-notify. also-notify is not meaningful for stub
zones. The default is the empty list.
The options statement sets up global options to be used by
BIND. This statement may appear at only once in a configuration
file; if more than one occurrence is found, the first occurrence
determines the actual options used, and a warning will be generated.
If there is no options statement, an options block with each option
set to its default will be used.
Pathnames
directory
The working directory of the server. Any non-absolute pathnames in the
configuration file will be taken as relative to this directory. The
default location for most server output files, for example,
"named.run" is this directory. If a directory is not specified,
the working directory defaults to ".", the directory from which the
server was started. The directory specified should be an absolute
path.
named-xfer
The pathname to the named-xfer program that the server uses
for inbound zone transfers. If not specified, the default is system
dependent for example, "/usr/sbin/named-xfer".
dump-file
The pathname of the file the server dumps the database to when it
receives SIGINT signal (ndc dumpdb). If not specified,
the default is "named_dump.db".
memstatistics-file
The pathname of the file the server writes memory usage statistics to
on exit, if deallocate-on-exit is yes. If not specified, the
default is "named.memstats".
pid-file
The pathname of the file the server writes its process ID in. If not
specified, the default is operating system dependent, but is usually
"/var/run/named.pid" or "/etc/named.pid". The pid-file
is used by programs like "ndc" that want to send signals to the
running nameserver.
statistics-file
The pathname of the file the server appends statistics to when it
receives SIGILL signal (ndc stats). If not specified, the
default is "named.stats".
Boolean Options
auth-nxdomain
If yes, then the AA bit is always set on NXDOMAIN
responses, even if the server is not actually authoritative. The default
is yes. Do not turn off auth-nxdomain unless you are sure you
know what you are doing, as some older software won't like it.
deallocate-on-exit
If yes, then when the server exits it will painstakingly deallocate
every object it allocated, and then write a memory usage report to the
memstatistics-file. The default is no, because it is faster to
let the operating system clean up. deallocate-on-exit is handy
for detecting memory leaks.
fake-iquery
If yes, the server will simulate the obsolete DNS query type
IQUERY. The default is no.
fetch-glue
If yes (the default), the server will fetch "glue" resource records it
doesn't have when constructing the additional data section of a response.
fetch-glue no can be used in conjunction with
recursion no to prevent the server's cache from growing or
becoming corrupted (at the cost of requiring more work from the
client).
host-statistics
If yes, then statistics are kept for every host that the nameserver
interacts with. The default is no.
NOTE: Turning on host-statistics can consume huge amounts of memory.
multiple-cnames
If yes, then multiple CNAME resource records will be allowed
for a domain name. The default is no. Allowing multiple CNAME
records is against standards and is not recommended. Multiple
CNAME support is available because previous versions of BIND
allowed multiple CNAME records, and these records have been used
for load balancing by a number of sites.
notify
If yes (the default), DNS NOTIFY messages are sent when a
zone the server is authoritative for changes. The use of NOTIFY
speeds convergence between the master and its slaves. Slave servers that
receive a NOTIFY message and understand it, will contact the
master server for the zone and see if they need to do a zone transfer,
and if they do, they will initiate it immediately. The notify option may
also be specified in the zone statement, in which case it overrides the
options notify statement.
recursion
If yes, and a DNS query requests recursion, then the server will
attempt to do all the work required to answer the query. If recursion is
not on, the server will return a referral to the client if it doesn't
know the answer. The default is yes. See also
fetch-glue.
Forwarding
The forwarding facility can be used to create a large sitewide
cache on a few servers, reducing traffic over links to external
nameservers. It can also be used to allow queries by servers that
do not have direct access to the Internet, but wish to look up exterior
names anyway. Forwarding occurs only on those queries for which
the server is not authoritative and does not have the answer in its cache.
forward
This option is only meaningful if the forwarders list is not empty.
A value of first, the default, causes the server to query the forwarders
first, and if that doesn't answer the question the server will then look
for the answer itself. If only is specified, the server will only query
the forwarders.
forwarders
Specifies the IP addresses to be used for forwarding. The default is
the empty list (no forwarding).
Future versions of BIND 8 will provide a more powerful forwarding system.
The syntax described above will continue to be supported.
Name Checking
The server can check domain names based upon their expected
client contexts. For example, a domain name used as a hostname can
be checked for compliance with the RFCs defining valid hostnames.
Three checking methods are available:
ignore
No checking is done.
warn
Names are checked against their expected client contexts. Invalid
names are logged, but processing continues normally.
fail
Names are checked against their expected client contexts. Invalid
names are logged, and the offending data is rejected.
The server can check names in three areas; master zone files, slave zone files,
and in responses to queries the server has initiated. If check-namesresponse fail has been specified, and answering the client's question
would require sending an invalid name to the client, the server will send a
REFUSED response code to the client.
The defaults are:
check-names may also be specified in the zone statement, in which case
it overrides the options check-names statement. When used in a zone
statement, the area is not specified (because it can be deduced from the zone
type).
Access Control
Access to the server can be restricted based on the IP address of the
requesting system. See address_match_list for details on how to
specify IP address lists.
allow-query
Specifies which hosts are allowed to ask ordinary questions.
allow-query may also be specified in the zone statement, in
which case it overrides the options allow-query statement. If
not specified, the default is to allow queries from all hosts.
allow-transfer
Specifies which hosts are allowed to receive zone transfers from the
server. allow-transfer may also be specified in the zone
statement, in which case it overrides the options allow-transfer
statement. If not specified, the default is to allow transfers from all
hosts.
Interfaces
The interfaces and ports that the server will answer queries from may be
specified using the listen-on option. listen-on takes an
optional port, and an address_match_list. The server will listen on
all interfaces allowed by the address match list. If a port is not specified,
port 53 will be used.
Multiple listen-on statements are allowed. For example:
If no listen-on is specified, the server will listen on port 53
on all interfaces.
Query Address
If the server doesn't know the answer to a question, it will query other
nameservers. query-source specifies the address and port used for such
queries. If address is * or is omitted, a wildcard IP address
(INADDR_ANY) will be used. If port is * or is omitted, a random
unprivileged port will be used. The default is
query-source address * port *;
NOTE: Query-source currently applies only to UDP queries; TCP queries
always use a wildcard IP address and a random unprivileged port.
Zone Transfers
max-transfer-time-in
Inbound zone transfers (named-xfer processes) running longer
than this many minutes will be terminated. The default is 120 minutes
(2 hours).
transfer-format
The server supports two zone transfer methods. one-answer
uses one DNS message per resource record transferred.
many-answers packs as many resource records as possible into a
message. many-answers is more efficient, but is only known to be
understood by BIND 8.1 and patched versions of BIND 4.9.5. The default is
one-answer. transfer-format may be overridden on a
per-server basis by using the server statement.
transfers-in
The maximum number of inbound zone transfers that can be running
concurrently. The default value is 10. Increasing transfers-in
may speed up the convergence of slave zones, but it also may increase the
load on the local system.
transfers-out
This option will be used in the future to limit the number of
concurrent outbound zone transfers. It is checked for syntax, but is
otherwise ignored.
transfers-per-ns
The maximum number of inbound zone transfers (named-xfer
processes) that can be concurrently transferring from a given remote
nameserver. The default value is 2. Increasing transfers-per-ns
may speed up the convergence of slave zones, but it also may increase the
load on the remote nameserver. transfers-per-ns may be
overridden on a per-server basis by using the transfers phrase
of the server statement.
Resource Limits
The server's usage of many system resources can be
limited. Some operating systems don't support some of the
limits. On such systems, a warning will be issued if the unsupported
limit is used. Some operating systems don't support limiting
resources, and on these systems a cannot set resource limits on
this system message will be logged.
Scaled values are allowed when specifying resource limits. For example,
1G can be used instead of 1073741824 to specify a limit of
one gigabyte. unlimited requests unlimited use, or the maximum available
amount. default uses the limit that was in force when the server was started.
See size_spec for more details.
coresize
The maximum size of a core dump. The default is default.
datasize
The maximum amount of data memory the server may use.
The default is default.
files
The maximum number of files the server may have open concurrently. The
default is unlimited.
NOTE: On some operating systems the server cannot set an unlimited value
and cannot determine the maximum number of open files the kernel can support.
On such systems, choosing unlimited will cause the server to use the larger of
the rlim_max for RLIMIT_NOFILE and the value returned by sysconf
(_SC_OPEN_MAX). If the actual kernel limit is larger than this value, use limit
files to specify the limit explicitly.
stacksize
The maximum amount of stack memory the server may use. The default is
default.
Periodic Task Intervals
cleaning-interval
The server will remove expired resource records from the cache every
cleaning-interval minutes. The default is 60 minutes. If set to
0, no periodic cleaning will occur.
interface-interval
The server will scan the network interface list every
interface-interval minutes. The default is 60 minutes. If set
to 0, interface scanning will only occur when the configuration file is
loaded. After the scan, listeners will be started on any new interfaces
(provided they are allowed by the listen-on configuration).
Listeners on interfaces that have gone away will be cleaned up.
statistics-interval
Nameserver statistics will be logged every
statistics-interval minutes. The default is 60. If set to 0, no
statistics will be logged.
Topology
All other things being equal, when the server chooses a nameserver to query
from a list of nameservers, it prefers the one that is topologically closest to
itself. The topology statement takes an address_match_list and
interprets it in a special way. Each top-level
list element is assigned a distance. Non-negated elements get a
distance based on their position in the list, where the closer the
match is to the start of the list, the shorter the distance is between
it and the server. A negated match will be assigned the maximum
distance from the server. If there is no match, the address will
get a distance which is further than any non-negated list element,
and closer than any negated element. For example,
topology {
10/8;
!1.2.3/24;
{ 1.2/16; 3/8; };
};
will prefer servers on network 10 the most, followed by hosts on network
1.2.0.0 (netmask 255.255.0.0) and network 3, with
the exception of hosts on network 1.2.3 (netmask 255.255.255.0), which
is preferred least of all.
The default topology is
BIND 4.9.x configuration files can be converted to the new format by using
src/bin/named/named-bootconf.pl, a perl script that is part of the
BIND 8.1 source kit.