It’s possible to find websites that belong to one owner or interconnected websites using DNS information, specifically IP addresses. This is not always 100 percent reliable, however, as websites that belong to many different owners can have the same IP address in shared hosting scenarios. Even so, sites that have the same IP address often belong to a single owner and it’s usually a fairly good indicator.
Also, it’s possible to locate shared Name Servers and the combination of those two things – shared IP address and Name Server – can significantly help the investigation.
All domains under a single IP can be checked, as well as all other domains hosted on the same Name Server. Reverse Name Server and Reverse IP Lookups can be effective methods to map domains together in the case where there is a common IP address or Name Server. This can be used both as a way to validate connections between unauthorized domains as well as to eliminate possible ‘false positives.’