Reverse IP Domain Check?

Question

There is a website which you can query with a domain and it will return a list of all the websites hosted on that IP. I remember there being a method in C# that was somethin

Answer 1

Jeremy's answer is based around Reverse DNS, which is the normal programmatical way to look up IP->hostname. It relies an a PTR record being set up for that server; this is often but not always set up to something useful.

For example look up, thedailywtf.com and you'll get 74.50.106.245, but since there is no PTR record for “245.106.50.74.in-addr.arpa”, Dns.GetHostEntry() won't return anything useful.

Similarly, many server farms will just give you a generic hostname like 123.45.67.89-dedicated.bigexamplehost.com.

What yougetsignal is doing is different, it's “Passive DNS Replication”. They run some DNS servers people are querying, and remember every hostname that was looked up. Then you can query their records of past lookups by the address that was returned. Put 74.50.106.245 into yougetsignal and you'll get a list of hostnames that previously resolved to the dailywtf server when people queried them, not anything to do with the Reverse DNS PTR entry.