My sites CMS has a manual page alias feature which is in wide use. I recently noticed that the aliased pages and the original pages are showing up in GA with separate traffic.For example:www.example.com/subfolder/pagename.aspxwww.example.com/pagename/these two pages are serving the exact same content from the cms, so it is in effect duplicate content which is bad for SEO. From this extremely helpful page it seems the best option is to add a  canonical link to the header. Can anyone verify that as the preferred solution?I would also like to know if this is a common problem among CMS platforms. The one we are using is called Ektron.
How should I fix the problem of duplicate content created by my CMS system's manual page alias feature?
seo;cms;canonical url
duplicate content by itself is not 'bad for SEO' (unless it's done on purpose to manipulate search engines). It has a slight effect in that the SE may decide to crawl, say, 1MB from your site today, and duplicate files will mean that less of your site gets crawled.  The other effect is that, when the search engine decides that your page shows as a result of a search, how does it know which of the two pages to show? (this is where the 'canonical' link acts. It tells the search engine use this page, otherwise the search engine will pick one of them at random which may not be your preferred URL to show)