Although Google is great at determining which site to credit the duplicate content to they can sometimes be mistakes which means your main site may be filtered out of the search results. For some websites there are however many legitimate duplicate sites, you may have caused a duplicate site for the following legitimate reasons

• Having another site for another market
• Migrating sites and not being able to redirect your old site to your new one

Google has released the rel=canonical tag to try and combat this duplicate content issue, this tag however only worked to combat internal duplicate content. The tag can now be used cross domain to resolve any legitimate external duplicate content issues you may have.

Below I have listed a few examples of how you should handle legitimate external duplicate content

• 1. Reduce internal duplication – Before looking to resolve external duplicate content you should resolve internal duplicate content with 301 redirects or canonical tags
• 2. Have a preferred domain – Search engines will generally filter your copied site out of the result pages, generally search engines are very good at this and will still keep your main domain in their index. However to ensure they index the correct site you should pick a domain and 301 the duplicate domains to it
• 3. Use the cross domain rel=canonical tag – If you don’t have the access to set up 301 redirects, or perhaps you are hosted on an IIS server you should use the cross domain rel=canonical tag. You should specify the exact URL for the preferred domain. Be careful though as Google has stated that this is only a hint and they won’t always follow it
• 4. Targeting mutiple countries – In some circumstances you may wish to target multiple countries with different domains. You will come accross a duplicate content issue with the same speaking countries, such as the UK, US and Austrailia. In this circumstance you should Geo Target your site to the appropriate country in Webmaster Tools. This will resolve the duplicate content issues as Google will now know the websites are for different markets

If you have any questions about any of my comments above don’t hesitate to contact me using the contact form on this site