Explanation of Zones in Alternate Access Mappings

Zones represent different logical paths (URLs) of gaining access to the same Web application. You can use zones to enforce different access and policy conditions for group of users.    
                                  

Each Web application can have a maximum of 5 zones. The 5 possible zones are:

·        Default:

·        Intranet

·        Internet

·        Custom

·        Extranet

When you create a Web application, the Default zone is created. You can then extend the Web application to create other zones.

Each zone can only be selected once per Web application. For example, you can only have one Default zone in a Web application.

Each zone is represented by a different Web site in IIS.

Configuration of AAM:
http://technet.microsoft.com/en-us/library/cc263208.aspx

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