Zone Data File Controls
The data files for all name servers, whether Microsoft or BIND, can include two control entries: $ORIGIN and $INCLUDE. $ORIGIN changes the origin, and $INCLUDE inserts a new file into the current file. These control entries are not resource records; they facilitate the maintenance of DNS data. They were designed back in the “good old days” as a shortcut for people who had to edit zone data files by hand. If you make changes to your zones with the DNS console only, you won’t encounter these controls: the Microsoft DNS Server doesn’t use them in the zone data files it generates. However, some day you might need to work with zone data files created by hand, so it’s important that you understand these controls.
Changing the Origin in a Data File
The default origin for a DNS data file is just the domain name of the zone. The origin is a domain name that is appended automatically to all names not ending in a dot. This origin can be changed within the zone data file using $ORIGIN, which must be followed by a domain name. (Don’t forget the trailing dot if you give the full domain name!) From that point in the file on, the new will be origin appended to all names not ending in a dot.
If we didn’t have the DNS console to make changes and had to edit files by hand, we’d run into times when $ORIGIN would save us some work. For example, if your name server were responsible for a number of subdomains, you could use the $ORIGIN entry to reset the origin and simplify ...