rocknbil - 7:16 pm on Feb 11, 2011 (gmt 0)

This is either a configuration at the hosting level or a mod_rewrite rule in .htaccess at the root of your domain. In either case it's a good thing that it's one or the other, your site's position in the serps is not divided among two different URL's - which is how the SE's would see them. The 301 redirect to one or the other puts all the weight in one URL for identical content, which is what you want.