Resolving the canonicalization issue can be a big headache because not all webmasters have the kind of server administration control that allows complete control over which version of your domain name is displayed to the world. However, it is important to note that while the optimal way to ensure that all search engines see only one version of your domain is by redirecting the non-canonical version to the canonical one, it’s not the only way.
First, the canonicalization issue is only an issue if search engines find your site under the “wrong” version. If search engine indexes are only showing your site under your preferred version, then it is less of a problem.
If you want to find out if your site has a problem, type site:yourdomain.com into the query box for each search engine like this:
If all the listings are for the same version of your domain as shown here, canonicalization is not yet a pressing issue for you:
However, this does not mean you are in the clear. Depending on how your site is built, all it would take is one other site to link to you using the non-canonical version and your site could end up with pages in search engine indexes from both versions of your domain. This could result in a canonicalization issue whereby some pages don’t receive the link value that they deserve and that can affect rankings.
To prevent this with Google, just register with Webmaster Tools and set a preferred domain. Other search engines do not have this option, so if you’re worried about how your results may be displayed in Yahoo or Live.com, a more universal fix may be in order.
What if you do have a problem? If your site is already showing pages from both versions of the domain in the index, using Google’s preferred domain tool is not the way to go. It can actually cause pages of your site to fall out of the index and this is definitely not a good solution. Poorly linked pages are better than no pages at all!
To make this a more universal fix, ensure that all the link references on your site are absolute rather than relational. What this means is that instead of linking to internal pages using code like this:
format all anchor tag link references to include the complete domain name:
This way, even if a spider does find one of your pages under the wrong version, it will not proceed to crawl the rest of the site under the wrong domain.
This last solution will work to resolve the canonicalization issue even if the search engines have already found your site under both versions, although not as quickly. By changing all link references on the site to refer to the absolute version of the preferred domain, eventually search engines will also prefer the pages from that preferred domain because the pages of the non-preferred version will show fewer in-bound links. Once these non-preferred pages have been replaced in the indexes, you can clinch the deal by setting your preferred domain with Google’s Webmaster Tools.