The preferred domain is the one that you would liked used to index your site's pages (sometimes this is referred to as the canonical domain). Links may point to your site using both the www and non-www versions of the URL (for instance, http://www.example.com and http://example.com). The preferred domain is the version that you want used for your site in the search results.
Once you tell us your preferred domain name, we use that information for all future crawls of your site and indexing refreshes. For instance, if you specify your preferred domain as http://www.example.com and we find a link to your site that is formatted as http://example.com, we follow that link as http://www.example.com instead. In addition, we'll take your preference into account when displaying the URLs. If you don't specify a preferred domain, we may treat the www and non-www versions of the domain as separate references to separate pages.
It may take some time before you see this change fully reflected in our index. All pages that currently display the non-preferred version of the URL in the index will remain in the index that way until we refresh our indexing of those pages.
Specify a preferred domain:
- On the Webmaster Tools Home page, click the site you want.
- Under Site configuration, click Settings.
- In the Preferred domain section, select the option you want.
You may need to verify ownership of both the www and non-www versions of your domain. Because setting a preferred domain impacts both crawling and indexing, we need to ensure that you own both versions. Typically, both versions point to the same physical location, but this is not always the case. Generally, once you have verified one version of the domain, we can easily verify the other using the original verification method. However, if you've removed the file, meta tag, or DNS record, you'll need to repeat the verification steps.
Note: Once you've set your preferred domain, you may want to use a 301 redirect to redirect traffic from your non-preferred domain, so that other search engines and visitors know which version you prefer.