Avoid Duplicate URL

To prevent users from linking to one version of a URL and others linking to a different version (this could split the reputation of that content between the URLs), focus on using and referring to one URL in the structure and internal linking of your pages. If you do find that people are accessing the same content through multiple URLs, setting up a 301 redirect from non-preferred URLs to the dominant
URL is a good solution for this.
Avoid:

• Having pages from subdomains and the root directory (e.g. "domain.com/page.htm" and "sub.domain.com/page.htm") access the same content
• Mixing www. and non-www. versions of URLs in your internal linking structure
• Using odd capitalization of URLs (many users expect lower-case URLs and remember them better)

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