This common DNS
trick is a part of every DNS geek
's knowledge base. It works
by using a CNAME record
on an in-addr.arpa 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
control over an in-addr.arpa zone
(i.e. for colocate
? Here's an example
Normally, an entry in a reverse resolve zone would look like this:
220.127.116.11.in-addr.arpa. IN PTR targethost.foo.com.
However, an entry in the reverse resolve zone using the CNAME trick looks like this:
18.104.22.168.in-addr.arpa. IN CNAME 192.168.20.1.foo.com.
Moving over to foo.com:
192.168.20.1.foo.com. IN PTR targethost.foo.com.
That way, the owner of foo.com 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 in-addr.arpa zone every time the hostname associated with the IP address (targethost.foo.com and 192.168.20.1, respectively) changes.