The YouGetSignal (http://www.yougetsignal.com/) is a website that provides a reverse IP lookup service. In layman’s terms, the website will try to get the IP address for every hostname entered and then it will do a reverse IP lookup on it, so it will discover other hostnames that are associated with that particular IP.
A classic situation is when the website is hosted on a shared server. If we had the task of penetrating a website, then we could do a reverse lookup for the website hostname on YouGetSignal and then attempt to break into other sites (if in scope). Then we could escalate privileges to get into the target website hosted on the same server.
Reverse IP domain check takes a domain name or IP address pointing to a web server and searches for other sites known to be hosted on that same web server. Data is gathered from search engine results, which are not guaranteed to be complete.
For demonstration purposes, I’ll do a reverse IP lookup through YouGetSignal on www.packtpub.com.
As you can see the feature provided us with the other websites on the same server which mean that these websites are sharing the same IP address and this step can help you to collect more info about your target.