Few IP's are making large amount of hits on our server. We are planning to block these IP's but before we lock IP's want to make sure if these are familiar to the site or not.
Having done the initial investigation of these IPs and carried out WHOIS lookup - many of these IPs look like hosting platforms.
United States Lexington Gomez Advisors
How and where can these be checked?
I'm not sure if I understand what if these are familiar to the site mean ...
If I get you correctly and someone tries (D)DoS on your servers he can do it from any IP if only he can control it (using virus, malware, etc).
I think better way is to take a look at other ways to prevent from DoS attacks, like reverse proxy: An effective defense against an HTTP flood can be the deployment of a reverse proxy.