What is a "C" Block Address?

[Bicoastal]

I have a silly question... What is a "C" Block Address?

I received a webmaster newsletter today with an article saying that an incoming link from a C Block Address should be avoided. But when I check my incoming links on link harvester they are all classified as C Block Addresses separated into different categories. I don't get it?

If someone could enlighten me, that would be great.

Thanks,

Bicoastal

[mcanerin]

A "C" Block address is based on your IP. In general, webhosts are given a different class C, so if you have a different C block, you are usually talking about two different webhosts.

I'm talking about the actual hardware owners here, of course. If two resellers of the same host sell you two hosting accounts, there is a good chance they are both on the same Class C.


Google assumes that sites hosted by two different hosts are probably separate, and therefore links between sites hosted on them are more likely to be from different people. There are problems with that assumption, but it's one of the things they look at anyway (gotta look at *something*).

Let's say you had an account with a shared IP address. So, for example, you had two sites that both used 192.168.5.1 as an IP. Google would tend to assume that these two sites are related, since they are on the same IP. This can be an issue with free or cheap hosts, which may have thousands of websites hosted on the same shared IP. You would normally try to avoid this if you had multiple sites that were likely to link to each other.

Now let's say that you got yourself 2 different (static) IP - your host would probably give you 192.168.5.2 and 192.168.5.3, in this example. Well these are two different IP's all right, but they are right next to each other, aren't they? Google would also likely consider these to be related.

But what if you hosted with another site across town? Perhaps they would be assigned a group of IP's to hand out that look like 192.168.122.XXX. Well, that 122 now indicates a different ISP, and therefore two sites hosted at this level are more likely to be considered unrelated.

To make a long story short:

192.168.006.001

is a standard, fully qualified IP address. The blocks in this case are:

AAA.BBB.CCC.001-254

That's not a Typo - Class D and E look totally different. The last 3 digits are actually called the Rest Field

So these are within the same class C:

192.168.222.111
192.168.222.230

And these are different Class C IP's:

192.167.111.233
192.168.222.233

Note: A class C is not the only thing Google looks at to detect relationships - telling someone to "get a different class C" is not necessarily a fix for anything.

Also, I run several websites on *gasp* a shared and dynamic IP - about the worst thing you can do as far as some of these SEO tech-heads will tell you. But I do very well in the SERPS, thank you very much.

IP's only become a real issue when you are looking at duplication issues, sites on related IP's coming up for the same keywords, and for significant amounts of interlinking, IMO.

For most people, there are a lot better and more effective things to think about. You should only worry about IP's if your rankings have given you a reason to worry about them, or if you are trying to spam the search engine (which I obviously don't recommend!).

In short, you should be aware of some of the issues, but for someone to say that you NEED different Class "C"'s is an exaggeration, IMO.

Ian

[AussieWebmaster]

Text book answer there Ian.

[Bicoastal]

Thanks Ian, now I get it...

But this really concerns me because I host about a dozen medical sites with Earthlink (Reseller Acct). Some are hosted on their Pasadena server and similar sites (not duplicates--they are more detailed, individual mini-sites broken out from a larger, broader topic--and do not cross link) are hosted on their Atlanta server. I notice that in link harvester that all the Pasadena sites have the same IP addresss--and Atlanta has a different one.

Most of these sites have been hosted for several years but still come up top 10 in the SERPs even though they ALL have the same registered owner. In google I hold the #1 (larger main site) and #3 position (detailed mini-site) for a particular keyword. But this now makes me nervous.

Is this something I should be worried about? Or planning for in the future?

The only reason I went with Earthlink to begin with is that when I first got into this business in 1995 my ISPs were going out of business all the time. I got tired of moving the sites every year so I went with the big guys thinking they would be around a while.

Bicoastal

[evilgreenmonkey]

From the way I understand your set-up, this should not be a problem. You only need to worry about IP addresses when sites are heavily interlinking with one another (appearing like doorway pages).