How to check reverse DNS

The DNS is used to determine what IP address is associated with a given host name, so to reverse resolve a known IP address is to lookup what the associated host name for it. A reverse lookup is often referred to simply as reverse resolving, or more specifically reverse DNS lookups.

Use of reverse DNS.

Anti-spam
Network troubleshooting
Avoid spammers and phishers using a forward confirmed reverse DNS etc

Check reverse DNS for given IP address under Linux or Windows XP/Server 2003.
You can use standard UNIX / Linux utilities such as nslookup, dig or hosts to find out reverse DNS of a given IP address.

eg; under Linux/UNIX/
$ host 66.65.123.34
or
dig -x IP (66.65.123.34)
and under Linux/UNIX/Windows
nslookup 66.65.123.34