12.3. Zone Files

Zone files contain information about a namespace and are stored in the named working directory, /var/named/, by default. Each zone file is named according to the file option data 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.
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 assign 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 be entered on individual lines.
Comments can be placed after semicolon characters (;) in zone files.

12.3.1. Zone File Directives

Directives begin with the dollar sign character ($) followed by the name of the directive. They usually appear at the top of the zone file.
The following are commonly used directives:
  • $INCLUDE — Configures named to include another zone file in this zone file at the place where the directive appears. This allows additional zone settings to be stored apart from the main zone file.
  • $ORIGIN — Appends the domain name to unqualified records, such as those with the hostname and nothing more.
    For example, a zone file may contain the following line:
    $ORIGIN example.com.
    Any names used in resource records that do not end in a trailing period (.) are appended with example.com.

    Note

    The use of the $ORIGIN directive is unnecessary if the zone is specified in /etc/named.conf because the zone name is used as the value for the $ORIGIN directive by default.
  • $TTL — Sets the default Time to Live (TTL) value for the zone. This is the length of time, in 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.