Reverse ip, find domain names on ip address

Question

How and from where websites like this http://www.yougetsignal.com/tools/web-sites-on-web-server/ are getting this information from? How can I develop such tool?

Thank you.

Answer 1

You can use nslookup on the IP. Reverse DNS is defined with the .in-addr.arpa domain.

Example:

nslookup somedomain.com

yields 123.21.2.3, and then you do:

nslookup 123.21.2.3

this will ask 3.2.21.123.in-addr.arpa and yield the domain name (if there is one defined for reverse DNS).