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Enabling Windows Server 2003 Functional Levels in a New Windows Server 2003 Forest

Updated: March 28, 2003

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

After you have installed the first domain controller in a new Windows Server 2003 forest, functional levels are set by default to the following levels, and remain at these levels until they are raised manually:

  • Windows 2000 mixed domain functional level

  • Windows 2000 forest functional level

Functional levels are set at these levels to allow you the option of adding Windows 2000 or Windows NT 4.0–based domain controllers to your new Windows Server 2003 forest.

After you create a forest root domain, the domain functional level for each additional domain that you add to the Windows Server 2003 forest is set to Windows 2000 mixed.


  • If the forest is operating at the Windows Server 2003 functional level, and you attempt to install Active Directory on a Windows 2000–based member server, the installation will fail. If you install Active Directory on a Windows Server 2003–based member server in order to create a new regional domain, the domain functional level is set to Windows Server 2003.

After you deploy the new Windows Server 2003 forest and the domain functional level is set in all domains, raise the domain functional level and then the forest functional level to Windows Server 2003. This enables you to take advantage of all Windows Server 2003 forest- and domain-level features. Thereafter, all new domains that you create are set at the Windows Server 2003 domain functional level.

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