Many webmasters will be happy to know that Google has announced its support for using the rel=”canonical” link element across different domains.
This is important news because when the canonical tag (as it’s become known) was introduced by all three search engines during our SMX West Conference this past February, they only supported its use inside a single domain. You could use the tag, for example, to indicate that yourdomain.com/page1.html was the canonical version of yourdomain.com/page2.html, and avoid duplicate content issues by doing so. Now, if you have a legitimate reason to have similar content on separate domains, Google will recognize your use of the rel=”canonical” link element.
Google has updated its webmaster help page to indicate how it supports the tag:
Can rel=”canonical” be used to suggest a canonical url on a completely different domain?
There are situations where it’s not easily possible to set up redirects. This could be the case when you need to migrate to a new domain name using a web server that cannot create server-side redirects. In this case, you can use the rel=”canonical” link element to specify the exact URL of the domain preferred for indexing. While the rel=”canonical” link element is seen as a hint and not an absolute directive, we do try to follow it where possible.
Google also has some additional Q&A posted on the blog announcement, so be sure to read that if you need more information.
Yahoo and Bing have not (yet?) announced cross-domain support for the rel=”canonical” link element.
Postscript: An update on Bing’s plans can be found here: Bing Still Working On Canonical Tag Support, Suggests Other Ways To Manage Duplicate Content