Several years ago, Google imposed host crowding filters to keep one domain from dominating the search results with multiple listings. They decided that only two results from any one domain should rank for any given search.

Many SEOs also believe that a host crowding filter can kick in on the Google results pages when two or more websites that are trying to rank for the same term or terms have the same IP address.

This is likely a reaction to the mini-nets that were so popular a few years back. With a mini-net, one created multiple small websites, all optimized for the same or very similar terms. Then, well-thought-out linking patterns were used to push PageRank to a main ”money” site, that focused on the sale or another form of conversion. Mini-nets were usually hosted together and host crowding filtering helped to prevent several sites in a network from all ranking for the same term(s).

Unfortunately, this filter means that if another website hosted on a shared IP address with your website outranks you for certain terms, your pages may never have a chance of ranking for those terms. This can be very discouraging, so what do you do?

Well, you can reoptimized your pages to rank for different terms or you can move your hosting. However, the very best option is to pay what it takes to have your very own IP address and not to share an address with any other websites.  (It’s okay to have several of your own sites share an IP address, as long as they are not optimized for the same terms.)

Having your own unique IP address also protects you from any fallout that can be brought on by sharing with a site that is flagged for web spam, email spam, adult content or other online evils. 

Until recently, subdomains snuck in under the radar of this Google filter because they were pretty much viewed as separate domains. In December of 2007, Google announced that they tweaked the host crowding filters to remove any slight advantage previously given to subdomains.