Implementing redirects is of the utmost importance when it comes to SEO. Whether running a Microsoft IIS or an Apache server, webmasters need the ability to implement redirects for old and alternate versions of your URLs. For example, if users are able to access the www version and non-www version of a website, these versions of the URLs are considered separate entities by the search engines and negative issues could arise.
For instance, both versions of your website could essentially be “diluting” your PageRank. If you have several inbound links to the www version of the site and several more pointing to the non-www version of the site, the importance Google assigns to you based on your inbound links is adversely affected. PageRank (represented by the little green icon on the Google toolbar) is the importance Google assigns to a page based on an automatic calculation that factors in the link structure of the web and many other variables. The green icon on the toolbar shows a scale of 1-10, with a PageRank of 10 being the highest. The magic numbers of 8-10 are usually reserved for the “big guns” such as Google, Yahoo and Amazon.com.
A page that is linked to by many pages with a high PageRank receives a high rank itself. If there are no or very few links to a web page there is no support for that page. Although it has been argued that there is very little correlation between PageRank and your actual rankings in Google, it is still an effective way to gauge how important Google thinks your website is. Once the correct redirects are implemented, the search engines should transfer link popularity from the old URL to the new one so that the search engine rankings are not affected. The same behavior occurs when additional domains are set to point to the main domain through a 301 redirect.
The search engine friendly way to redirect URLs is to use what is know as a 301 (Moved Permanently) redirect. Multiple domains (www vs. non-www or separate domains publishing the exact content) can be deemed to be duplicate content by the search engines and your website could get penalized with automatic “de-indexing” or rank reduction in the search engines. Avoiding this is crucial to your website’s SEO success and survival.