As the discussion on duplicate content drones on (to the dismay of some), it's only natural that some really excellent how to guides come about. Part of the duplicate content discussion is the best way to avoid domain and canonical URL issues when linking internally, fixing typos in URL's, and redirects on your site. WebmasterWorld has one of the best technical guides that I have seen of late on how to fix these duplicate content issues in Google that arise from some of the URL canonicalization issues.
For those that need a refresher on about URL canonicalization, it is summarized as "choosing what single domain you want to use for your site, and what single URL should be used to request each of your pages," having urls that are outside this standard can cause problems in the search engines and part of this guide instructs you how to fix that. According to jdMorgan, the following are some step you can take to ensure you are not in terrority where duplicate content would be flagged on your pages:
- Canonicalize the domain (e.g. redirect non-www and IP address to www)
- Canonicalize my index pages (redirect "/index.html" to "/")
- Remove multiple slashes in the URL
- Remove spurious query strings (my sites' pages are mostly 'static' with a few exceptions)
- Fix-up common typos in type-in URLs
- Fix-up invalid inbound links caused by bad HTML mark-up
- Fix-up URLs resulting from bad copy-and-pastes
- Fix-up outdated or otherwise incorrect query strings
- Suppress the fix-up redirect if the resulting URL does not resolve to an existing file
- Suppress the fix-up if the link is on my own site (In this case, I want to see the 404 error)
- Suppress the fix-up if the remote user is me or a site tester (Again, we want to see the 404 error)
- Avoid recursion in mod_rewrite running in a per-directory .htaccess context
- Avoid the nasty mod_rewrite bug in Apache 1.3.x
- Do all of the above using a single 301-Moved Permanently redirect
Definately worth a look at this thread. Continued discussion at WebmasterWorld - Guide to Fixing URL Canonicalization isssues
