Lot of new webmasters keeps asking me what is C class IP, so its simple if you see any ip address its divided in to 4 parts – AAA.BBB.CCC.DDD. Third section is called Class IP.
Whats the importance of C class IP in SEO?
In the era of spam, many webmasters started creating multiple website on same server and linked each other to increase the sites backlink and ranking. Search Engines identified this issue and started avoiding links coming from similar IPs – given its easy to get different D class ips on same server, Search Engines also started avoiding Links from same C Class IP. So when Search Engine see that you’ve a link coming from same C Class IP on which your website is located, the backlink will not have any importance. Please note you’ll not get penalized if you’ve link coming from same C class IP, but you’ll not get any advantage either. So if you are doing the link exchange specially if you don’t have your own server, do check if the person you are linking to has a different C class ip than yours.
Recommended C class IP checker Tool : http://www.validrank.com/pages/class-c.php