I’ve been in contact with a client’s developer this past few days regarding URL rewrites of plain old *.html files to *.aspx. The SEO principle involve in this is pretty simple, “301 redirect all old *.html pages to each equivalent new *.aspx pages”. This is pretty tricky and requires more advance coding skills and familiarity with server side scripting, but once implemented properly, you don’t have to worry about URL rewrites affecting your search engine rankings.
Why use 301 redirect?
There are several types of redirects to choose from, but 301 redirect which stands for “permanent redirection” transfers link power from the old pages to new pages.
What if im having problems with my webhost and I can’t do 301 or any server redirects?
Many developers would be tempted to use client-side redirects as a substitute, but the best thing you can do is use the “rel=canonical” element. Place this canonical element in “<head>”section of all “*.html” pages and use the new *.aspx” pages as target href of the canonical element.