This common DNS trick is a part of every DNS geek's knowledge base. It works by using a CNAME record on an hostname instead of a PTR record. The idea being that the owner of the hostname of the CNAME record will be able to manipulate it to his will. This is commonly used for when an ISP wants to relinquish only partial control over an zone (i.e. for colocate purposes). Confused? Here's an example:

Normally, an entry in a reverse resolve zone would look like this: IN PTR

However, an entry in the reverse resolve zone using the CNAME trick looks like this: IN CNAME

Moving over to      IN PTR

That way, the owner of has ultimate control of the reverse resolve by using his own zone. This is opposed to having to get ahold of the owner of the zone every time the hostname associated with the IP address ( and, respectively) changes.

Cool, huh?
