In a previous article, you learned about the four domain functional levels that are supported under Windows Server 2003. Knowing the domain functional levels is important if you are on your way to achieving an MCSA or MCSE. However, you also need to know the forest functional levels, as well.
Windows Server 2003 supports the following three different functional levels:
- Windows 2000
- Windows Server 2003 Interim
- Windows Server 2003
Windows 2000 is the default forest functional level. It provides support for Windows NT, 2000, and 2003 domain controllers. Under this functional level, all the features included with Windows 2000 are supported.
Windows Server 2003 Interim
This forest functional level is normally used when upgrading from Windows NT to Windows Server 2003. This is the recommended forest level when performing upgrades. However, Windows 2000 domain controllers are not supported.
Windows Server 2003
The third forest functional level is Windows Server 2003. As the name implies, only domain controllers running Windows Server 2003 are supported. Once you upgrade to this level, no domain controllers running previous versions of Windows can be added to the forest. However, all the advanced features of Windows Server 2003 are activated.
You can find out more about the three forest functional levels from this Microsoft Knowledge Base article.