Sub-domains are websites that are located within a directory of your main site and have their own domain name. Because they use the same resources as the main website, they are normally much cheaper than getting another hosting account. Their low cost and flexibility make sub-domains a great device for directing traffic to your site without breaking the bank.

*Sub-domains as Portal Sites*
One of the best uses of sub-domains is portal websites. Portal websites are sites that link to your main website and have a similar theme. Basically, they provide another portal, or doorway, for visitors and search engines to get to your main website.

Since creating content for a website takes time, often webmasters simply modify the existing text of the main site and reuse it on the portal site. It is important that the content is not exactly the same and the portals do not just redirect to the main site. Otherwise, search engines may not index them.

*More Portals, More Visitors*
Portal websites can be submitted to the search engines just like your main site. If your website is doing alright in the search engines, then imagine having five more websites out there for the spiders to find. Five more listings means that Web surfers have five times as many ways to find your network of websites.

*Search Engines and Links*
More and more search engine algorithms take into consideration the number and ranking of sites that link to you. By linking your sub-domains to your main site and to each other, the ranking of all of your sites is improved.

*Banner Exchange Programs*
Banner exchange programs allow members to share advertising space on each other