Google supports cross domain canonical link element
It came as no suprise to hear Google officially announce support for the canonical link element, what came as a suprise was that it came before the christmas break. News of impending cross-domain support was announced by Google back in October at SMX East as a means of handling legitimate cross domain content duplication.
The webmaster help pages advise further of how this should be correctly utilised
Can rel=”canonical” be used to suggest a canonical url on a completely different domain?
Yahoo and Bing have both formally to announce support, however it should be noted that Google do still advise this should be a last resort, and other avenues should potentially be considered before utilising rel="canonical".
Where possible, the most important step is often to use appropriate 301 redirects. These redirects send visitors and search engine crawlers to your preferred domain and make it very clear which URL should be indexed. This is generally the preferred method as it gives clear guidance to everyone who accesses the content. Keep in mind that in order for search engine crawlers to discover these redirects, none of the URLs in the redirect chain can be disallowed via a robots.txt file. Don't forget to handle your www / non-www preference with appropriate redirects and in Webmaster Tools.
However there are certain situations where this may not be possible, for example on hosts where 301's may not be able to be configured. The following points taken from the Official Google announcement should also be considered
The news has been generally greeted positively by the industry, however it will still be interesting to see the takeup of this in general.
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