Functional levels determine the features that are available and the domain controllers that are supported. In a previous article, you learned about the three domain functional levels that are supported under Windows Server 2008. There are also functional levels at the forest level.

Windows Server 2008 supports the following three forest functional levels:

• Windows 2000 Native
• Windows Server 2003 Interim
• Windows Server 2003

Windows 2000 Native

Windows 2000 native is the default forest functional level. It provides support for Windows 2000, 2003 and 2008 domain controllers. This functional level support all of the default AD DS features.

Windows Server 2003

This forest functional level supports Windows Server 2003 and 2008 domain controllers. Along with the default features, the following features are introduced at this level:

• Forest trust
• Domain rename
• Linked-value replication
• Read-only domain controller
• Improved Knowledge Consistency Checker
• Ability to create the dynamic auxiliary class named dynamicObject
• Ability to create instances on new group types to support role-based authorization
• Deactivation and redefinition of attributes and classes in the schema

Windows Server 2009

The third forest functional level is Windows Server 2008. As the name implies, only domain controllers running Windows Server 2008 are supported. No additional features are introduced at this level.