It has been documented that Google, among other search engines, adds value to domains that have static IP addresses. I suppose that Google must view the expenditure on a static IP address as a sign of how serious the webmaster or domain owners’ intentions are moving forward. It would make sense that spam sites would go through a great expense to get all of their autogenerated websites on separate IP address’s. This would also go hand and hand with the information about the length of domain registration and age of domain having significant influence on your search results.

You may have heard of people in the link building world discussing C Class IP adddress. This is the 3 block of numbers in an IP address which is usually the one that remains static when assigning IP address to multiple domains on one server.

Example: An IP consist of 4 parts AAA.BBB.CCC.xxx - the first part is called A-class, the second part B-class and the third part C-class. So any IP under the last part will be in the same C-class. So for example:

111.222.333.1 and 111.222.333.2 are in the same C-class but
111.222.332.1 and 111.222.333.1 are in two different C-classes

Most small hosts manage very few C Class IP addresses. The search engines have discovered in the past link builders whom had multiple sites on the same C class IP linking to one another.  Google has since devalued or removed any value from links from the same C class IP addresses. They have also reduced the ability of multiple sites on one IP to pass link juice to any other website.

Until recently hosts did not care about keeping sites on dedicated C class IP’s. Recently you have seen a rise on SEO (search engine optimization) hosting services. These are people who have figured this C class IP address formula out and are offering the ability to have lots of C class IP addresses.