Is the fact that the same page using non-www and www URLs and get 2 identical pages with different page ranks important. Does google really think I have 2 identical home pages? Can this cause me to be penalized?
The problem is when I do a redirect it interferes with my shopping cart causing a script error.

Google will consider as Two different this better we need to put 301 redirect for website.

you have put redirection for this page. if you will not duplication problem will create . so its better to put 301 redirection.

Offcourse those are treated as different pages and there are cent percentage chances that your site will get penalized. 301 redirection is one solutions and another is to configure through webmasters.

Unlike DNS, Google can't determine the changes in the pages of the same URL. That's where 301 redirect comes in

301 redirect rules in that case. Google can determine the main mirror itself, the question is whether this will be the one you want to be the main.

A small code in .htaccess file can do a redirection for you. make sure to setup permission as 755.




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Tier 2

301 error is a serious issue in SEO, after panda updates, is has become more important than earlier. Now if you webpage has 301 error, Google will consider them duplicate page.