Before you start
Objectives: Learn what are domain and forest functional levels.
Prerequisites: no prerequisites.
Key terms: domain, forest, functional level
Functional Levels
A functional level determines which functions are available in our Active Directory domain or forest. In different situations we will have different functional level, depending on the existing constraints. Functional level defines which Active Directory Domain Services (AD DS) will be available to the domain or forest and which Windows Server operating systems can be run on domain controllers in the domain or forest. When it comes to workstations that we join to our domain (or servers that we join to our domain), we don’t have to worry about functional levels. So, functional levels don’t affect operating systems that we can run on workstations.
Different versions of Windows Server OS will support different domain and forest functional levels. For example, Windows Server 2008 supports the following domain functional levels:
- Windows 2000 Native
- Windows Server 2003
- Windows Server 2008
Windows Server 2008 supports the following forest functional levels:
- Windows 2000
- Windows Server 2003
- Windows Server 2008
One thing to keep in mind is that we cannot have Windows NT domain controllers and Windows Server 2008 domain controllers in the same forest.