Reverse ip, find domain names on ip address

You can use ping -a <ip> or nbtstat -A <ip>

They're just trawling lists of web sites, and recording the resulting IP addresses in a database.

All you're seeing is the reverse mapping of that list. It's not guaranteed to be a full list (indeed more often than not it won't be) because it's impossible to learn every possible web site address.

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).