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C.2. named.conf Configuration Commands

The named.conf file defines the name server configuration and tells named where to obtain the name server database information. BIND 8 uses the following configuration commands: key, acl, options, logging, zone, server, controls, and trusted-keys. BIND 9 uses the same eight commands and adds the view command.

In addition to these configuration commands, both BIND 8 and BIND 9 provide an include statement used to load an external file that contains any of the configuration commands. For example:

include /var/named/keys

copies the file /var/named/keys, which might be a file containing key and trusted-key commands into the named.conf file.

C.2.4. The server Statement

The server statement defines the characteristics of a remote server. The BIND 8 syntax is:

server address {
  [ bogus yes|no; ]
  [ support-ixfr yes|no; ]
  [ transfers number; ]
  [ transfer-format one-answer|many-answers; ]
  [ keys { key_id [key_id ... ] }; ]
};

The server statement applies to the remote server identified by address.

transfer-format

Sets the format used for zone transfers with this server to either the more efficient many-answers format or the backward-compatible one-answer format.

bogus yes

Prevents the local server from sending queries to this server. The default is no, which permits queries to the remote server.

support-ixfr yes

Indicates that the remote server can support incremental transfers. no, which is the default, says that the remote server cannot perform incremental transfers.

transfers

Defines the maximum number of concurrent inbound transfers permitted from this server.

keys

Identifies the key required by the remote host for transaction security.

C.2.5. The options Statement

The options statement defines global options for BIND and the DNS protocol. The BIND 8 syntax of the options command is:

options {
  [ version string; ]
  [ directory pathname; ]
  [ named-xfer pathname; ]
  [ dump-file pathname; ]
  [ memstatistics-file pathname; ]
  [ pid-file pathname; ]
  [ statistics-file pathname; ]
  [ auth-nxdomain yes|no; ]
  [ deallocate-on-exit yes|no; ]
  [ dialup yes|no; ]
  [ fake-iquery yes|no; ]
  [ fetch-glue yes|no; ]
  [ has-old-clients yes|no; ]
  [ host-statistics yes|no; ]
  [ multiple-cnames yes|no; ]
  [ notify yes|no; ]
  [ recursion yes|no; ]
  [ rfc2308-type1 yes|no; ]
  [ use-id-pool yes|no; ]
  [ treat-cr-as-space yes|no; ]
  [ also-notify { address-list; };
  [ forward only|first; ]
  [ forwarders { address-list; }; ]
  [ check-names master|slave|response  warn|fail|ignore; ]
  [ allow-query { address_match_list }; ]
  [ allow-transfer { address_match_list }; ]
  [ allow-recursion { address_match_list }; ]
  [ blackhole { address_match_list }; ]
  [ listen-on [ port ip_port ] { address_match_list }; ]
  [ query-source [address ip_addr|*] [port ip_port|*] ; ]
  [ lame-ttl number; ]
  [ max-transfer-time-in number; ]
  [ max-ncache-ttl number; ]
  [ min-roots number; ]
  [ serial-queries number; ]
  [ transfer-format one-answer|many-answers; ]
  [ transfers-in  number; ]
  [ transfers-out number; ]
  [ transfers-per-ns number; ]
  [ transfer-source ip_addr; ]
  [ maintain-ixfr-base yes|no; ]
  [ max-ixfr-log-size number; ]
  [ coresize size; ]
  [ datasize size; ]
  [ files size; ]
  [ stacksize size; ]
  [ cleaning-interval number; ]
  [ heartbeat-interval number; ]
  [ interface-interval number; ]
  [ statistics-interval number; ]
  [ topology { address_match_list }; ]
  [ sortlist { address_match_list }; ]
  [ rrset-order { order_spec ; [ order_spec ; ... ] ] };
};

There are almost a dozen different types of values for these options. Two options, check-names and transfer-format, accept keyword values. Boolean options accept either yes or no. All other options expect an appropriate value in a specific format. Some formats (string, number, pathname, domain, type, class, ip_port, and ip_addr) are self-explanatory. Some formats require a little explanation:.

address-list

A list of IP addresses separated by semicolons. This is more limited than an address_match_list.

address_match_list

A list of addresses, acl names, and key_ids.

order_spec

A multi-part rule that defines how resource records are ordered when multiple records are sent in response to a single query. The structure of an order_spec is:

[ class class ][ type type ][ name "domain" ] order order

class, type and domain are self-explanatory. order is one of three possible values:

fixed

The order in which records are defined in the zone file is maintained.

random

Resource records are shuffled into a random order.

cyclic

The resource records are rotated in a round-robin manner, which is the default order.

The BIND 8 options are:

version

The string returned when the server is queried for its version.

directory

The path of the working directory from which the server reads and writes files.

named-xfer

The path to the named-xfer program.

dump-file

The file where the database is dumped if named receives a SIGINT signal. The default filename is named_dump.db.

memstatistics-file

The file where memory usage statistics are written. The default filename is named.memstats.

pid-file

The file where the process ID is stored.

statistics-file

The file where statistics are written when named receives a SIGILL signal. The default filename is named.stats.

auth-nxdomain

yes, which is the default, causes the server to respond as an authoritative server.

deallocate-on-exit

yes writes memory usage to the named.memstats file. The default is no.

dialup

yes optimizes the server for a dial-up network operation. The default is no.

fake-iquery

yes makes the server issue a fake reply instead of an error in response to inverse queries. The default is no.

fetch-glue

yes, which is the default, retrieves all of the glue records for a response.

has-old-clients

yes sets auth-nxdomain and maintain-ixfr-base to yes and rfc2308-type1 to no.

host-statistics

yes keeps statistics on every host. The default is no.

multiple-cnames

yes permits multiple CNAME records for a domain name. The default is no.

notify

yes, which is the default, sends DNS NOTIFY messages when a zone is updated.

recursion

yes, the default, recursively seeks answers to queries.

rfc2308-type1

yes returns NS records with the SOA record for negative caching. no, the default, returns only the SOA record for compatibility with old servers.

use-id-pool

yes tracks outstanding query IDs to increase randomness. no is the default.

treat-cr-as-space

yes treats carriage returns as spaces when loading a zone file. no is the default.

also-notify

Identifies unofficial name servers to which the server should send DNS NOTIFY messages.

forward

first causes the server to first query the forwarders and then look for the answer itself. only causes the server to query only the forwarders.

forwarders

Lists the IP addresses of the servers to which queries are forwarded. The default is not to use forwarding.

check-names

Checks hostnames for compliance with the RFC specifications. Names can be checked when the master server loads the zone (master), when the slave transfers the zone (slave), or when a response is processed (response). If an error is detected, it can be ignored (ignore), a warning can be sent (warn), or the bad name can be rejected (fail).

allow-query

Only queries from hosts in the address list will be accepted. The default is to accept queries from all hosts.

allow-transfer

Only hosts in the address list are allowed to receive zone transfers. The default is to allow transfers to all hosts.

allow-recursion

Only listed hosts are allowed to make recursive queries through this server. The default is to do recursive queries for all hosts.

blackhole

Lists hosts from which this server will not accept queries.

listen-on

Defines the interfaces and ports on which the server provides name service. By default, the server listens to the standard port (53) on all installed interfaces.

query-source

Defines the address and port used to query other servers.

lame-ttl

The amount of time a lame server indication will be cached. The default is 10 minutes.

max-transfer-time-in

The maximum amount of time the server waits for an inbound transfer to complete. The default is 120 minutes (2 hours).

max-ncache-ttl

The amount of time this server will cache negative answers. The default is 3 hours and the maximum acceptable value is 7 days.

min-roots

The minimum number of root servers that must be reachable for queries involving the root servers to be accepted. The default is 2.

serial-queries

The number of outstanding SOA queries a slave server can have at one time. The default is 4.

transfer-format

one-answer transfers one resource record per message. many-answers transfers as many resource records as possible in each message.

transfers-in

Sets the maximum number of concurrent inbound zone transfers. The default value is 10.

transfers-out

Lists the number of concurrent outbound zone transfers.

transfers-per-ns

Limits the number of concurrent inbound zone transfers from any one name server. The default value is 2.

transfer-source

The IP address of the network interface this server uses to transfer zones from remote masters.

maintain-ixfr-base

yes keeps a log of incremental zone transfers. no is the default.

max-ixfr-log-size

Sets the maximum size of the incremental zone transfer log file.

coresize

Sets the maximum size of a core dump file.

datasize

Limits the amount of data memory the server may use.

files

Limits the number of files the server may have open concurrently. The default is unlimited.

stacksize

Limits amount of stack memory the server may use.

cleaning-interval

Sets the time interval for the server to remove expired resource records from the cache. The default is 60 minutes.

heartbeat-interval

Sets the time interval used for zone maintenance when the dialup option is set to yes. 60 minutes is the default.

interface-interval

Sets the time interval for the server to scan the network interface list looking for new interfaces or interfaces that have been removed. The default is every 60 minutes.

statistics-interval

Sets the time interval for the server to log statistics. The default is every 60 minutes.

topology

Forces the server to prefer certain remote name servers over others. Normally, the server prefers the remote name server that is topologically closest to itself.

sortlist

Defines a sort algorithm applied to resource records before sending them to the client.

rrset-order

Specifies the ordering used when multiple records are returned for a single query.

C.2.5.1. The BIND 9 options statement

The BIND 9 syntax of the options command is:

options {
  [ version string; ]
  [ directory pathname; ]
  [ additional-from-auth yes|no; ] 
  [ additional-from-cache yes|no; ]
  [ dump-file pathname; ]
  [ pid-file pathname; ]
  [ statistics-file pathname; ]
  [ auth-nxdomain yes|no; ]
  [ dialup yes|no; ]
  [ notify yes|no|explicit; ] 
  [ notify-source [ip_addr|*] [port ip_port] ; ]
  [ notify-source-v6 [ip_addr|*] [port ip_port] ; ]
  [ recursion yes|no; ]
  [ recursive-clients number; ] 
  [ tcp-clients number; ]
  [ also-notify { address-list; };
  [ forward only|first; ]
  [ forwarders { address-list; }; ]
  [ allow-notify { address_match_list }; ]
  [ allow-query { address_match_list }; ]
  [ allow-transfer { address_match_list }; ]
  [ allow-recursion { address_match_list }; ]
  [ blackhole { address_match_list }; ]
  [ listen-on [ port ip_port ] { address_match_list }; ] 
  [ listen-on-v6 [ port ip_port ] { address_match_list }; ]
  [ port ip_port; ]
  [ query-source [address ip_addr|*] [port ip_port|*] ; ] 
  [ query-source-v6 [address ip6_addr|*] [port ip_port|*] ; ]
  [ lame-ttl number; ]
  [ max-transfer-time-in number; ] 
  [ max-transfer-time-out number; ] 
  [ max-transfer-idle-in number; ] 
  [ max-transfer-idle-out number; ] 
  [ max-refresh-time number; ] 
  [ max-retry-time number; ] 
  [ max-cache-ttl number; ]
  [ max-ncache-ttl number; ]
  [ min-refresh-time number; ] 
  [ min-retry-time number; ]
  [ transfer-format one-answer|many-answers; ]
  [ transfers-in  number; ]
  [ transfers-out number; ]
  [ transfers-per-ns number; ]
  [ transfer-source ip_addr|*] [port ip_port|*]; ] 
  [ transfer-source-v6 ip6_addr|*] [port ip_port|*]; ]
  [ coresize size; ]
  [ datasize size; ]
  [ files size; ]
  [ stacksize size; ]
  [ cleaning-interval number; ]
  [ heartbeat-interval number; ]
  [ interface-interval number; ]
  [ sortlist { address_match_list }; ]
  [ sig-validity-interval number; ]
  [ tkey-dhkey key_name key_tag; ]
  [ tkey-domain domain; ]
  [ zone-statistics yes|no; ]
};

Many BIND 9 options are the same as those used for BIND 8 and perform exactly the same functions. A few options have been added to BIND 9 to handle IPv6, which is an integral part of BIND 9. These options, listen-on-v6, notify-source-v6, query-source-v6, and transfer-source-v6, perform exactly the same functions as the like-named options do for IPv4. Many BIND 8 options are no longer needed because important functions have been incorporated into the new BIND 9 code. However, the list of options is no shorter because many new options have been added:

additional-from-auth

yes, the default, causes the server to use information from any zone for which it is authoritative when completing the additional data section of a response.

additional-from-cache

yes, the default, causes the server to use information from its cache when completing the additional data section of a response.

notify-source

Defines the address and port used to send NOTIFY messages.

recursive-clients

Defines the maximum number of outstanding recursive lookups the server will perform for its clients. The default is 1000.

tcp-clients

Defines the maximum number of concurrent client connections. The default is 1000.

allow-notify

Identifies the servers that are permitted to send NOTIFY messages to the slave servers.

port

Defines the port number used by the server. The default is standard port 53.

max-transfer-time-out

Defines the maximum time allowed for outbound zone transfers. The default is 2 hours.

max-transfer-idle-in

Defines the maximum time that an inbound zone transfer will be allowed to sit idle. The default is 1 hour.

max-transfer-idle-out

Defines the maximum time that an outbound zone transfer will be allowed to sit idle. The default is 1 hour.

max-refresh-time

Sets the maximum refresh time this server will use when acting as a slave. This value overrides the refresh time set in the SOA record of the zone for which this server acts as a slave.

max-retry-time

Sets the maximum retry time this server will use when acting as a slave. This value overrides the retry time set in the SOA record of the zone for which this server acts as a slave.

max-cache-ttl

Sets the maximum amount of time this server will cache data. This value overrides the TTL values defined in the zone from which the data was retrieved.

min-refresh-time

Sets the minimum refresh time this server will use when acting as a slave. This value overrides the refresh time set in the SOA record of the zone for which this server acts as a slave.

min-retry-time

Sets the minimum retry time this server will use when acting as a slave. This value overrides the retry time set in the SOA record of the zone for which this server acts as a slave.

sig-validity-interval

Defines the amount of time that digital signatures generated for automatic updates will be considered valid. The default is 30 days.

tkey-dhkey

Identifies the Diffie-Hellman key used by the server to generate shared keys.

tkey-domain

Defines the domain name appended to shared keys. Normally this is the server's domain name.

zone-statistics

yes causes the server to collect statistics on all zones. The default is no.

Options change over time. Check the documentation that comes with the BIND 9 distribution for the latest list of options.

C.2.6. The logging Statement

The logging statement defines the logging options for the server. The logging statement can include two different types of subordinate clauses: the channel clause and the category clause. The BIND 8 syntax of the command is:

logging {
  [ channel channel_name {
     file pathname
       [ versions number|unlimited ]
       [ size size ]
    |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|no; ]
    [ print-severity yes|no; ]
    [ print-time yes|no; ]
  }; ]

  [ category category_name {
    channel_name; [ channel_name; ... ]
  }; ]
  ...
};

The channel clause defines how logging messages are handled. Messages are written to a file (file), sent to syslog (syslog), or discarded (null). If a file is used, you can specify how many old versions are retained (version), how large the log file is allowed to grow (size), and the severity of the messages written to the log file (severity). You can specify that the time (print-time), category (print-category), and severity (print-severity) of the message be included in the log.

The category clause defines the types of messages sent to the channel. Thus the category clause defines what is logged, and the channel clause defines where it is logged. The categories are listed in Table C-1.

Table C-1. BIND 8 logging categories

Category

Type of messages logged

cname

Messages recording CNAME references.

config

Messages about configuration file processing.

db

Messages that log database operations.

default

Various types of messages. This is the default if nothing is specified.

eventlib

Messages containing debugging data from the event system.

insist

Messages that report internal consistency check failures.

lame-servers

Messages about lame server delegations.

load

Messages about loading the zone.

maintenance

Messages reporting maintenance events.

ncache

Messages about negative caching.

notify

Messages tracing the NOTIFY protocol.

os

Messages reporting operating system problems.

packet

Messages containing dumps of all of the packets sent and received.

panic

Messages generated by a fault that causes the server to shut down.

parser

Messages about configuration command processing.

queries

Messages about every DNS query received.

response-checks

Messages reporting the results of response checking.

security

Messages concerning the application of security criteria. These are most meaningful if allow-update, allow-query, and allow-transfer options are in use.

statistics

Messages containing server statistics.

update

Messages concerning dynamic updates.

xfer-in

Messages recording inbound zone transfers.

xfer-out

Messages recording outbound zone transfers.

C.2.7. The zone Statement

The zone statement identifies the zone being served and defines the source of DNS database information. There are four variants of the zone statement: one for the master server, one for the slave servers, one for the root cache zone, and a special one for forwarding. The BIND 8 syntax of each variant is:

zone domain_name [ in|hs|hesiod|chaos ] { 
  type master;
  file pathname;
  [ forward only|first; ]
  [ forwarders { address-list; }; ]
  [ check-names warn|fail|ignore; ]
  [ allow-update { address_match_list }; ]
  [ allow-query { address_match_list }; ]
  [ allow-transfer { address_match_list }; ]
  [ dialup yes|no; ]
  [ notify yes|no; ]
  [ also-notify { address-list };
  [ ixfr-base pathname; ]
  [ pubkey flags protocol algorithm key; ]
};

zone domain_name [ in|hs|hesiod|chaos ] { 
  type slave|stub;
  [ file pathname; ]
  [ ixfr-base pathname; ]
  masters [port ip_port]{ address-list };
  [ forward only|first; ]
  [ forwarders { address-list; }; ]
  [ check-names warn|fail|ignore; ]
  [ allow-update { address_match_list }; ]
  [ allow-query { address_match_list }; ]
  [ allow-transfer { address_match_list }; ]
  [ transfer-source ip_addr; ]
  [ dialup yes|no; ]
  [ max-transfer-time-in number; ]
  [ notify yes|no; ]
  [ also-notify { address-list };
  [ pubkey flags protocol algorithm key; ]
};

zone "." [ in|hs|hesiod|chaos ] { 
  type hint;
  file pathname;
  [ check-names warn|fail|ignore; ]
};

zone domain_name [in|hs|hesiod|chaos] { 
  type forward;
  [ forward only|first; ]
  [ forwarders { address-list; }; ]
  [ check-names warn|fail|ignore; ]
}; 

The zone keyword is followed by the name of the domain. For the root cache, the domain name is always ".". The domain name is followed by the data class. This is always IN for Internet DNS service, which is the default if no value is supplied.

The type clause defines whether this is a master server, a slave server, a forwarded zone, or the hints file for the root cache. A stub server is a slave server that loads only the NS records instead of the entire domain.

The file clause for a master server points to the source file from which the zone is loaded. For the slave server, it points to the file to which the zone is written, and the master clause points to the source of the data written to the file. For the root cache, the file clause points to the hints file used to initialize the cache. A forwarded domain does not have a file clause because no data for the forwarded domain is stored on the local server.

With the exception of the pubkey option, all of the options available for the BIND 8 zone statement are covered earlier in this appendix. When defined in a zone statement, an option applies only to the specific zone. When specified in the options statement, an option applies to all zones. The specific settings for a zone override the global settings of the options statement.

The pubkey option defines the DNSSEC public encryption key for the zone when there is no trusted mechanism for distributing public keys over the network. pubkey defines the DNSSEC flags, protocol, and algorithm as well as a base64-encoded version of the key. The remote server that will be accessing this domain through DNSSEC defines the same settings using the trusted-key command described earlier in this appendix.

C.2.7.1. The BIND 9 zone statement

The BIND 9 syntax of the four zone statement variants is:

zone domain_name [ in|hs|hesiod|chaos ] { 
  type master;
  file pathname;
  [ forward only|first; ]
  [ forwarders { address-list; }; ]
  [ allow-update { address_match_list }; ] 
  [ allow-update-forwarding { address_match_list }; ]
  [ allow-query { address_match_list }; ]
  [ allow-transfer { address_match_list }; ]
  [ allow-notify { address_match_list }; ]
  [ dialup yes|no; ]
  [ notify yes|no|notify|notify-passive|refresh|passive; ]
  [ also-notify { address-list };
  [ database string; [...] ]
  [ update-policy { policy }; ]
  [ sig-validity-interval number; ]
  [ max-refresh-time number; ] 
  [ max-retry-time number; ] 
  [ max-transfer-idle-out number; ] 
  [ max-transfer-time-out number; ] 
  [ min-refresh-time number; ] 
  [ min-retry-time number; ]
};

zone domain_name [ in|hs|hesiod|chaos ] { 
  type slave|stub;
  [ file pathname; ]
  [ ixfr-base pathname; ]
  masters [port ip_port]{ address-list };
  [ forward only|first; ]
  [ forwarders { address-list; }; ]
  [ check-names warn|fail|ignore; ]
  [ allow-update { address_match_list }; ]
  [ allow-update-forwarding { address_match_list }; ]
  [ allow-query { address_match_list }; ]
  [ allow-transfer { address_match_list }; ]
  [ transfer-source ip_addr; ]
  [ dialup yes|no|notify|notify-passive|refresh|passive; ]
  [ max-transfer-time-in number; ]
  [ notify yes|no; ]
  [ also-notify { address-list };
  [ max-refresh-time number; ] 
  [ max-retry-time number; ] 
  [ max-transfer-idle-in number; ] 
  [ max-transfer-idle-out number; ] 
  [ max-transfer-time-in number; ] 
  [ max-transfer-time-out number; ] 
  [ min-refresh-time number; ] 
  [ min-retry-time number; ]  
  [ transfer-source ip_addr|*] [port ip_port|*]; ] 
  [ transfer-source-v6 ip6_addr|*] [port ip_port|*]; ]
};

zone "." [ in|hs|hesiod|chaos ] { 
  type hint;
  file pathname;
};

zone domain_name [in|hs|hesiod|chaos] { 
  type forward;
  [ forward only|first; ]
  [ forwarders { address-list; }; ]
}; 

BIND 9 uses the same four zone command variations as does BIND 8. The difference between the two versions of BIND is that they use different options. Most of the options shown in the BIND 9 syntax were explained in the discussion of the BIND 9 options statement. The two options that are unique to the BIND 9 zone statement are:

allow-update-forwarding

Identifies the systems that are allowed to submit dynamic zone updates to a slave that will then be forwarded to the master.

database

Specifies the type of database used for storing zone data. The default is rbt, which is the only database type supported by the standard BIND 9 executable.

C.2.8. The controls Statement

The BIND 8 controls statement defines the control channels used by ndc. ndc can use a Unix socket or a network socket as a control channel. The controls statement defines those sockets. The syntax is:

controls {
  [ inet ip_addr 
    port ip_port 
    allow { address_match_list; }; ]
  [ unix pathname 
    perm file_permissions
    owner uid
    group gid; ]
};

The first three options, inet, port, and allow, define the IP address and the port number of a network socket and the access control list of those systems allowed to control named through that channel. Because BIND 8 has weak authentication, creating a control channel that is accessible from the network is a risky thing to do. Whoever gains access to that channel has control over the name server process.

The last four options, unix, perm, owner, and group, define the Unix control socket. The Unix socket appears as a file in the filesystem. It is identified by a normal file pathname, for example, /var/run/ndc. Like any file, the Unix socket is assigned the user ID (uid) of its owner and a valid group ID (gid). It is protected by standard file permissions. Only numeric uid, gid, and file_permissions values are acceptable. The file_permissions value must start with a 0. For example, to set owner read and write, group read, and world no permissions, the numeric value would be 0640.



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