Do search engines penalize related/linked sites that are hosted on the same class C network?
I say NO, it’s much worse than that. Here’s why: there is much more information out there to need to rely on a simplified class C network address analysis.
I’ve heard certain authorities state that hosting multiple sites on a single IP address will not help positioning in search engine rankings. This is mostly in regard to interlinking sites that are all hosted on the same IP address. There are also people that say it is just as bad to host/interlink sites that reside in the same class C address space. I think that most people underestimate the amount of information that is available to search engines and how that information is used. I’m specifically referring to WHOIS. Most people know that WHOIS contains information about owners of domains. But did you know that it also contains information about owners of netblocks?
(Disclaimer: I have no affiliation with Vortech Inc. I have never hosted with them and am only using them as an example of how much information is available through WHOIS.)
A WHOIS query on this address (whois.arin.net) reveals that there are 16 neighboring class C address spaces that they own
“CIDR: 126.96.36.199/20” which is equivalent to the addresses 188.8.131.52 – 184.108.40.206. Why wouldn’t the search engines use this more reliable information instead of fixating on class C address spaces?
To take it a step further, run a whois query on “Vortech Inc.” You’ll notice that they have control of many network blocks:
Vortech Inc. (VTC1)
Vortech Inc. (AS32065) VORTECH-INC 32065
Vortech Inc. VORTECH-BLK-1 (NET-216-157-128-0-1) 220.127.116.11 – 18.104.22.168
Vortech Inc. VORTECH-BLK-2 (NET-216-81-64-0-1) 22.214.171.124 – 126.96.36.199
Vortech Inc. VORTECH-BLOCK-1 (NET-66-103-145-0-1) 188.8.131.52 – 184.108.40.206
Vortech Inc. VORTECH-BLOCK-2 (NET-66-103-153-0-1) 220.127.116.11 – 18.104.22.168
Vortech Inc. VORTECH-BLOCK-4 (NET-72-21-10-0-1) 22.214.171.124 – 126.96.36.199
Vortech Inc. VORTECH-BLOCK-3 (NET-66-103-149-0-1) 188.8.131.52 – 184.108.40.206
If I’m running related and inter-linked flower shop sites on different network blocks at Vortech, it’s easy as a search engine to flag those sites since they are hosted by the same provider.
The WHOIS Goldmine
Ok, just one more step of paranoia. It’s also easy to look at the WHOIS information of one domain that is linking to another and look for similarities (name, address, phone, zip code) and assess the chances of those domains having some sort of relationship. I’ve been told that amateurs use their real information when registering their domains, intermediates use some sort of privacy guard or proxy to shield their information, and the experts just put fake information in when registering their domains. I do not condone the third method because ICANN states that domain registration information needs to be correct and up to date.
So, put on your tinfoil hats and be careful what you do and say. Somebody is always watching you.