Zone File Directives

RFC 1035 defines a number of directives for use in zone files. These are summarised below:

• $TTL - Mandatory as first entry in a BIND 9 zone file. Defines the default TTL (or cache life) for any Resource Record which does not contain one.
• $ORIGIN - changes the 'zone name' which is added to any 'unqualified' name. The dot is optional at the end of a name appearing in an ORIGIN directive.
• $INCLUDE - allows the contents of a file to be inserted into the zone file. The critical point to note is that if an INCLUDE'd file contains an $ORIGIN statement it's scope (is valid) for the INCLUDE'd file only, the original values of ORIGIN and 'zone name' are restored once the INCLUDE'd file has been fully processed.

BIND additionally provides $GENERATE, a non-standard directive to simplify generation of reverse delegations in in-addr.arpa files. If you think you may want to change DNS software do not use $GENERATE.