The Global Redirect module is extremely important to use when enabling the Pathauto module. Essentially, the Pathauto module will generate the appropriate aliases. However, it does not delete the old ones. So, if you had an alias of http://www.example.com/keyword1/keyword2.htm for the path http://www.example.com/node/23, you would be able to access the page from either URL. This will result in duplicate content.

What Global Redirect will do:

• checks to see if the current URL has an existing alias, and if it does, it will automatically perform a 301 redirect to that alias
• check if the current URL is marked as the front page and will redirect if so
• verify that the url is being generated in clean mode
• check for a trailing slash at the end of the URL and remove it if it exists to keep files consistent

This module is easy to use as you simply need to enable it in your modules setting. Global Redirect will automatically do the rest.

NOTE: If you change your Pathauto aliases for whatever reason, Global Redirect will not redirect your old alias to your new one. You will have to do a 301 Redirect in your .htaccess file to accomplish this.