Configuring and Managing MPE/iX Internet Services > Appendix C BIND 8.1 Enhanced Features

BIND 8 Highlights

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DNS Dynamic Updates (RFC 2136)
DNS Change Notification (RFC 1996)
Completely new configuration syntax
Flexible, categorized logging system
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.

BIND Configuration File Guide — Logging Statement

Syntax


  logging {
    [ channel channel_name {
       ( file path_name
          [ versions ( number | unlimited ) ]
          [ size size_spec ]
        | syslog ( kern | user | mail | daemon | auth | syslog | lpr | 
          news | uucp | cron | authpriv | ftp |
          local0 | local1 | local2 | local3 |
          local4 | local5 | local6 | local7 )
     | null );
  [ severity ( critical | error | warning | notice |
               info | debug [ level ] | dynamic ); ]
    [ print-category yes_or_no; ]
    [ print-severity yes_or_no; ]
    [ print-time yes_or_no; ]
    }; ]
  [ category category_name {
    channel_name; [ channel_name; ... ]
    }; ]
    ...
  };

Definition and Usage

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:


  logging {
          category default { default_syslog; default_debug; };
          category panic { default_syslog; default_stderr; };
          category packet { default_debug; };
          category eventlib { default_debug; };
  };

The Channel Phrase

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,


      channel specific_debug_level {
          file "foo";
          severity debug 3;
      };

will get debugging output of level 3 or less any time the server is in debugging mode, regardless of the global debugging level. Channels with dynamic severity use the server's global 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 internal 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:


     category default { default_syslog; default_debug; };

As an example, you want to log security events to a file, but you also want keep the default logging behavior. You'd specify the following:


     channel my_security_channel {
         file "my_security_file";
         severity info
     };
     category security { my_security_channel; default_syslog; default_debug; };

To discard all messages in a category, specify the null channel:


     category lame-servers { null; };
     category cname { null; };

The following categories are available:

default

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:


  category default { default_syslog; default_debug; };

config

High-level configuration file processing.

parser

Low-level configuration file processing.

queries

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 ...".

BIND Configuration File Guide—Zone Statement

Syntax


  zone domain_name [ ( in | hs | hesiod | chaos ) ] {
       type master;
       file path_name;
       [ check-names ( warn | fail | ignore ); ]
       [ allow-update { address_match_list }; ]
       [ allow-query { address_match_list }; ]
       [ allow-transfer { address_match_list }; ]
       [ notify yes_or_no; ] [ also-notify { ip_addr; [ ip_addr; ... ] };
  };


  zone domain_name [ ( in | hs | hesiod | chaos ) ]
       { type ( slave | stub );
       [ file path_name; ]
       masters { ip_addr; [ ip_addr; ... ] };
       [ check-names ( warn | fail | ignore ); ]
       [ allow-update { address_match_list }; ]
       [ allow-query { address_match_list }; ]
       [ allow-transfer { address_match_list }; ]
       [ max-transfer-time-in number; ]
       [ notify yes_or_no; ]
       [ also-notify { ip_addr; [ ip_addr; ... ] };
  };


  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.

BIND Configuration File Guide — Options Statement

Syntax


  options {
     [ directory path_name; ]
     [ named-xfer path_name; ]
     [ dump-file path_name; ]
     [ memstatistics-file path_name; ]
     [ pid-file path_name; ]
     [ statistics-file path_name; ]
     [ auth-nxdomain yes_or_no; ]
     [ deallocate-on-exit yes_or_no; ]
     [ fake-iquery yes_or_no; ]
     [ fetch-glue yes_or_no; ]
     [ host-statistics yes_or_no; ]
     [ multiple-cnames yes_or_no; ]
     [ notify yes_or_no; ]
     [ recursion yes_or_no; ]
     [ forward ( only | first ); ]
     [ forwarders { [ in_addr ; [ in_addr ; ... ] ] }; ]
     [ check-names ( master | slave | response ) ( warn | fail | ignore); ]
     [ allow-query { address_match_list }; ]
     [ allow-transfer { address_match_list }; ]
     [ listen-on [ port ip_port ] { address_match_list }; ]
     [ query-source [ address ( ip_addr | * ) ]
     [ port ( ip_port | * ) ] ; ]
     [ max-transfer-time-in number; ]
     [ transfer-format ( one-answer | many-answers ); ]
     [ transfers-in number; ]
     [ transfers-out number; ]
     [ transfers-per-ns number; ]
     [ coresize size_spec ; ]
     [ datasize size_spec ; ]
     [ files size_spec ; ]
     [ stacksize size_spec ; ]
     [ cleaning-interval number; ]
     [ interface-interval number; ]
     [ statistics-interval number; ]
     [ topology { address_match_list }; ]
  };

Definition and Use

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-names response 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 master fail;
  check-names slave warn;
  check-names response ignore;

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:


  listen-on { 5.6.7.8; };
  listen-on port 1234 { !1.2.3.4; 1.2/16; };

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


  topology { localhost; localnets; };

Converting From BIND 4.9.x

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.

Appendix C BIND 8.1 Enhanced Features

Appendix D Server Configuration Migration

BIND 8 Highlights

MPE documents

BIND Configuration File Guide — Logging Statement

Syntax

Definition and Usage

The Channel Phrase

The Category Phrase

BIND Configuration File Guide—Zone Statement

Syntax

Definition and Usage (Zone Types)

Class

Options

BIND Configuration File Guide — Options Statement

Syntax

Definition and Use

Pathnames

Boolean Options

Forwarding

Name Checking

Access Control

Interfaces

Query Address

Zone Transfers

Resource Limits

Periodic Task Intervals

Topology

Converting From BIND 4.9.x