Guide- How to deal with Duplicate Content different solutions. This great article was published by Ben Jarriola at SEOmoz.

Alternate Link Tag –  Meta Robots
Canonical Link Tag –  301 Redirect –  Robots.txt

• Alternate Link Tag
  • International pages, multilingual pages, intended for different countries.

• Canonical Link Tag
  • Multiple categories and subcategories with different category paths, but the same content.
    Example:

    http://www.example.com/products/laptops/sony/

    http://www.example.com/products/sony/laptops/

  • Tracking codes, Session IDs mainly because redirection sometimes interferes with the functionality of the tracking codes and sessions.
    Example:

    http://www.example.com/path/file.php?SID=BG47JF448JD6I7TGF439LVFD476

    http://www.example.com/path/file.php?utm_whatever=5uck3rs

    http://www.example.com/path/file.php

  • Different variable orders due to how some CMS platforms are created.
    Example:

    http://www.example.com/path/file.php?var1=x&var2=y

    http://www.example.com/path/file.php?var2=y&var1=x

• 301 Redirect
  • Cases where a redirection does not bother the user experience such as www and non-www, index files, trailing slashes, hosting IP address.
    Example:

    http://www.example.com/

    http://example.com/

    http://www.example.com/index.html

    http://www.example.com

    http://123.123.123.123/

  • Domain changes, and URL changes of pages that no longer exist.
    Example:
    http://www.example.com/old_folder/old_file 301 redirects to http://www.example.com/new-folder/new-file/
    http://www.example.net/ 301 redirects to http://www.example.com/

• Meta Robots NoIndex/Follow
  • Probably the best place to use this is in a list of archived post, such as a blog. Where the main URL of the individual blog post or the permalink may have content that is posted as a duplicate somewhere in the archive view by date, the category view, the author view, tag topic views, or in the pagination of older blog post from the blog homepage. You cannot really do a 301 redirect, nor do a canonical link tag since these pages may have more than 1 blog post listed and you will have to finalized where the 301 redirect should go or where the canonical link tag should point to. Thus I would take my chances using the Meta Robots tag, NoIndex,Follow, and hopefully all the links still help.

• Robots.txt
  • I no longer see a need to use robots.txt in duplicate content issues. The natural linking is something too precious to lose. Just use robots.txt to really block of content that does not need to be indexed at all, duplicate content or not.