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Thanks. Why is it not available on tools page?

Hi Amarjit, If you set up the preferred domain in Google Webmaster, in reality that should be fine for most SEO purposes. That said, it's still best practices to redirect visitors to one version or another. It's doubtful you'll see much SEO benefit from it, but it might make things easier from a consistancy point of view, and it's long been a regular practice of most SEOs. You can read more about it here: http://www.seomoz.org/learn-seo/redirection Best of luck!