Zone Files - Red Hat ENTERPRISE LINUX 3 Reference Manual

Chapter 12. Berkeley Internet Name Domain (BIND)

12.3. Zone Files

Zone files contain information about a namespace and are stored in the
, by default. Each zone file is named according to the
/var/named/
statement, usually in a way that relates to the domain in question and identifies the file as containing
zone data, such as
example.com.zone
Each zone file may contain directives and resource records. Directives tell the nameserver to perform
tasks or apply special settings to the zone. Resource records define the parameters of the zone and as-
sign identities to individual hosts. Directives are optional, but resource records are required to provide
name service to a zone.
All directives and resource records should go on their own individual lines.
Comments can be placed after semicolon characters (
12.3.1. Zone File Directives
Directives begin with the dollar sign character (
appear at the top of the zone file.
The following are commonly used directives:
— Configures
• $INCLUDE
directive appears. This allows additional zone settings to be stored apart from the main zone file.
— Appends the domain name to unqualified records, such as those with the hostname
•
$ORIGIN
and nothing more.
For example, a zone file may contains the following line:
$ORIGIN example.com
Any names used in resource records that do not end in a trailing period (
appended to them.
Note
The use of the
because the zone name is used as the value for the
— Sets the default Time to Live (TTL) value for the zone. This is the length of time, in
• $TTL
seconds, a zone resource record is valid. Each resource record can contain its own TTL value,
which overrides this directive.
Increasing this value allows remote nameservers to cache the zone information for a longer period
of time, reducing the number of queries for the zone and lengthening the amount of time required
to proliferate resource record changes.
12.3.2. Zone File Resource Records
The primary component of a zone file is its resource records.
There are many types of zone file resource records. The following are used most frequently:
— Address record, which specifies an IP address to assign to a name, as in this example:
• A
host IN
If the value is omitted, then an
host
namespace. This system is the target for all non-FQDN requests.
.
to include another zone file in this zone file at the place where the
named
directive is unnecessary if the zone is specified in
$ORIGIN
A IP-address
) in zone files.
;
) followed by the name of the directive. They usually
$
$ORIGIN
record points to a default IP address for the top of the
A
working directory,
named
option data in the
file
) will have
. example.com
/etc/named.conf
directive by default.
189
zone