The below video explains how to test to see if you have the Apache Mod_Rewrite already setup to remove duplicate URLs:
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Here’s a great site on how to use Apache Mod_Rewrite to automatically rewrite your URLs so it always has “www” before the domain name. Without this, people can access the same content either by going to http://domainname.com/file.html or http://www.domainname.com/file.html which will dilute your linking for that URL. This site gives more information on the importance of it, but believe me it’s IMPORTANT!
http://www.thesitewizard.com/apache/redirect-domain-www-subdomain.shtml
