DNS

What is DNS

DNS Explained on Wiki

Why Reverse DNS required

http://en.wikipedia.org/wiki/Domain_Name_System#Reverse_lookup

http://en.wikipedia.org/wiki/Reverse_DNS_lookup

DNS Video: Basics and DNS Zones

http://www.youtube.com/watch?v=srBQSzRRNF4

http://www.youtube.com/watch?v=WYCPTuGNj7U

http://www.youtube.com/watch?v=R6wxLjKkXCI

http://www.youtube.com/watch?v=72snZctFFtA

http://pctechstream.com

DNS Management Software for Linux

PTR is reverse lookup..