When you are submitting your websites to web directories it is important that your links come from web directories with different Class C IPs. This will tell the search engines that your links are coming from different sources and not from network sites that are created to promote a particular website. It is not an uncommon practice to create a network of websites by webmasters to create back links for a target website. All these network websites were hosted in the same server. Search engines soon realized the pattern of links created using network sites and such links were not given credit by search engines. Sometimes, websites that used such link building practices were penalized by the search engines