SEO hosting is sometimes called C-Class IP hosting. It uses multiple C-Class IP addresses so that search engines recognize them discretely, even though they reside on the same server.
Ordinarily, if you were to create numerous websites with the same IP address, at a certain point, search engines would recognize this and filter them out. Internet Vikings holds 160,000 IP addresses derived from 35 A-Class, 70 B-Class, and 1200 C-Class IPs.