Raise the Functional Levels of Domains and Forests
Applies To: Windows Server 2008, Windows Server 2008 R2
To enable all Windows Server 2008 advanced features in Active Directory Domain Services (AD DS), raise the functional level of your forest to Windows Server 2008. This will automatically raise the functional level of all domains to Windows Server 2008. To enable all Windows Server 2008 R2 advanced AD DS features, raise the functional level of your forest to Windows Server 2008 R2. This will automatically raise the functional level of all domains to Windows Server 2008 R2.
Warning
Do not raise the forest functional level to Windows Server 2008 R2 if you have or will have any domain controllers running Windows Server 2008 or earlier.
Important
After you set the forest functional level to a certain value, you cannot roll back or lower the forest functional level, with one exception: when you raise the forest functional level to Windows Server 2008 R2 and if Active Directory Recycle Bin is not enabled, you have the option of rolling the forest functional level back to Windows Server 2008. You can lower the forest functional level only from Windows Server 2008 R2 to Windows Server 2008. If the forest functional level is set to Windows Server 2008 R2, it cannot be rolled back, for example, to Windows Server 2003.
For more information about the Active Directory Recycle Bin, see Active Directory Recycle Bin Step-by-Step Guide (https://go.microsoft.com/fwlink/?LinkId=133971).
Use the following procedure to raise the forest functional level to Windows Server 2008.
Membership in Domain Admins or Enterprise Admins, or equivalent, is the minimum required to complete this procedure. Review details about using the appropriate accounts and group memberships at Local and Domain Default Groups (https://go.microsoft.com/fwlink/?LinkId=83477).
To raise the forest functional level
Open the Active Directory Domains and Trusts snap-in. Click Start, click Administrative Tools, and then click Active Directory Domains and Trusts.
In the console tree, right-click Active Directory Domains and Trusts, and then click Raise Forest Functional Level.
In Select an available forest functional level, do one of the following:
To raise the forest functional level to Windows Server 2003, click Windows Server 2003, and then click Raise.
To raise the forest functional level to Windows Server 2008, click Windows Server 2008, and then click Raise.
To raise the forest functional level to Windows Server 2008 R2, click Windows Server 2008 R2, and then click Raise.
For more information about Windows Server 2008 advanced AD DS features, see Enabling Advanced Features for AD DS.