Large sections of content within a domain that are a close or exact match are considered duplicate content by Google. Although the occurrence is usually unintentional, this could have a negative impact on SEO.

A few examples of non-malicious duplicate content identified by Google are:

• Discussion forums that generate stripped-down pages targeted at mobile devices in addition to regular content
• Multiple distinct URLs pointing to the same product in a store
• “Printer-only” iterations of pages

Here are a few suggestions from Google to address issues with duplicate content:

• Use 301 redirects (“RedirectPermanent”) in your .htaccess file to smartly redirect users, Googlebot, and other spiders.
• Keep your internal linking consistent. For example, don’t link to http://www.site.com/page/ and http://www.site.com/page and http://www.site.com/page/index.htm.
• Use top-level domains to help Google serve the most appropriate version of a document (http://www.site.de instead of http://www.site.com/de or http://de.site.com).
• Use Google Webmaster Tools to indicate how you prefer your site to be indexed: (http://www.site.com or http://site.com).
• Minimize similar content: expand the content of each page if a two exist with extensive similarities, or consolidate the two into a single page.