Raising the Roof on Domain Functional Levels
Elevating your Windows Server 2003 Active Directory domain and forest functional levels can deliver enhanced functionality, but is it worth the time and hassle?
For many administrators, domain functional levels on Windows Server 2003 are somewhat of an afterthought. Because the default domain functional level works adequately for most environments, the procedure for raising the domain functional level is seen as an unnecessary complication. In reality, the raising procedure is straightforward and the benefits gained can prove to be well worth the minimal investment in time required to perform the raising procedure.
In simple terms, the domain functional level dictates the implementation of Active Directory that is in use on your network. As you would expect, the higher the domain functional level, the more functionality that is available. In some cases, the additional functionality might be in the form of features, such as the ability to deactivate unnecessary attributes from the schema, that may not interest you all that much. In other cases, features like the ability to configure caller ID recognition for remote access users make the justification behind raising the domain functional level much clearer.
Domain functional levels are not a new concept in Active Directory, although in Windows 2000 Server they are referred to as ‛modes,’ and there are only two of them: Native and Mixed. Windows Server 2003 increases the number of domain functional levels available to four: Windows 2000 Mixed, Windows 2000 Native, Windows Server 2003 Interim, and Windows Server 2003.
The default domain functional level for a newly installed Windows Server 2003 system is actually Windows 2000 mixed, even if it is the first and only Windows Server 2003 domain controller on the network. The Windows 2000 Mixed domain functional level is the most versatile, as it supports Windows NT 4.0, Windows 2000, and Windows Server 2003 domain controllers. However, it also offers the lowest level of functionality.
In comparison, Windows 2000 Native supports Windows 2000 Server and Windows Server 2003 systems, and provides enhancements over the Windows 2000 Mixed domain functional level. You should use the Windows 2000 Native domain functional level if you intend to keep both Windows 2000 Server and Windows Server 2003 domain controllers on the network.
The Windows Server 2003 domain functional level only supports Windows Server 2003 domain controllers and offers the highest level of functionality. The Windows Server 2003 Interim domain functional level is only used when you are in the process of upgrading Windows NT 4.0 domain controllers to Windows Server 2003. One key consideration for the above information is that the domain functional level only affects domain controllers, not member (stand-alone) servers.