10.3. Editing Zone Files

As outlined in Section 10.1.1, “Nameserver Zones”, zone files contain information about a namespace. They are stored in the named working directory located in /var/named/ by default, and each zone file is named according to the file option in the zone 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.

Table 10.5. The `named` service zone files

Path	Description
`/var/named/`	The working directory for the `named` service. The nameserver is not allowed to write to this directory.
`/var/named/slaves/`	The directory for secondary zones. This directory is writable by the `named` service.
`/var/named/dynamic/`	The directory for other files, such as dynamic DNS (DDNS) zones or managed DNSSEC keys. This directory is writable by the `named` service.
`/var/named/data/`	The directory for various statistics and debugging files. This directory is writable by the `named` service.

A zone file consists of 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 assign identities to individual hosts. While the directives are optional, the resource records are required in order to provide name service to a zone.

All directives and resource records should be entered on individual lines.

10.3.1. Common Directives

Directives begin with the dollar sign character (that is, $) followed by the name of the directive, and usually appear at the top of the file. The following directives are commonly used in zone files:

$INCLUDE

The $INCLUDE directive allows you to include another file at the place where it appears, so that other zone settings can be stored in a separate zone file.

Example 10.7. Using the `$INCLUDE` directive

$INCLUDE /var/named/penguin.example.com

$ORIGIN

The $ORIGIN directive allows you to append the domain name to unqualified records, such as those with the hostname only. Note that the use of this directive is not necessary if the zone is specified in /etc/named.conf, since the zone name is used by default.

In Example 10.8, “Using the $ORIGIN directive”, any names used in resource records that do not end in a trailing period (that is, the . character) are appended with example.com.

Example 10.8. Using the `$ORIGIN` directive

$ORIGIN example.com.

$TTL

The $TTL directive allows you to set the default Time to Live (TTL) value for the zone, that is, how long is a zone record 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.

Example 10.9. Using the `$TTL` directive

$TTL 1D