If you are studying for your MCSA or MCSE certification, you may have already come across the various domain functional levels. There are four different domain functional levels in Windows Server 2003. You need to be familiar with each of the four levels and what you can or can not do at each one.

The four domain functional levels are:

• Windows 2000 Mixed

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

Windows 2000 Mixed
When you configure a new Windows Server 2003 domain, the default domain functional level is Windows 2000 mixed. Under this domain functional level, Windows NT, 2000, and 2003 domain controllers are supported. However, certain features such as group nesting, universal groups, and so on are not available.

Windows 2000 Native
Upgrading the functional level of a domain to Windows 2000 Native should only be done if there are no Windows NT domain controllers remaining on the network. By upgrading to Windows 2000 Native functional level, additional features become available including: group nesting, universal groups, SIDHistory, and the ability to convert security groups and distribution groups.

Windows Server 2003 Interim
The third functional level is Windows Server 2003 Interim and it is often used when upgrading from Windows NT to Windows Server 2003. Upgrading to this domain functional level provides support for Windows NT and Windows Server 2003 domain controllers. However, like Windows 2000 Mixed, it does not provide new features.

Windows Server 2003
The last functional level is Windows Server 2003. This domain functional level only provides support for Windows Server 2003 domain controllers. If you want to take advantage of all the features included with Windows Server 2003, you must implement this functional level. One of the most important features introduced at this functional level is the ability to rename domain controllers.

Read this knowledge base article to find out more information about domain functional levels under Windows Server 2003.