what is effect of c class IP related to seo?

[RK]

[Peter]

Class C refers to the third set of numbers in an IP.
AAA.BBB.CCC.DDD

If all the links came from the same C subnet, they're 'likely' less trusted.

The 'theory' (calling it a theory because i don't think its ever really been proven) is that multiple links from the same C subnet are less valuable because its likely that they come from an owner of multiple websites.

I wouldn't label them as 'bad'

But if you're link building, it's probably a good idea to get links from different subnets

[Jake]

To clarify the fundamentals, before there were countless free social hosts from which to get backlinks, it was standard procedure to create a network of your own sites to provide backlinks to boost the ranking of the main money site. Search engines give little credit to links between your own properties, webmasters try to conceal the common owner with private domain registration or different registration information, and sites on different hosts with IP addresses different enough to not appear to be the same host.
Search engines probably assume 2 different sites with the same (or close to the same) IP address are on the same file server and are likely to have the same owner.

[Richard]

Basically, Google prefer backlinks to come from natural sources (like other websites willingly linking to you). So the more diverse, the IP address of the linking source, the more natural it may seem.