Taking Advantage of Functional Levels

Many of the items discussed in this chapter are new Windows Server 2003 features that are only available when domain controllers are operating in Windows Server 2003 functional modes. In essence, to get some of the new features available to Active Directory, all domain controllers must be running Windows Server 2003.

The functional levels of Windows Server 2003 are similar to the mixed and native modes of Windows 2000 Active Directory. They provide for backward-compatibility to earlier operating systems and a migration path to the newest operating system. This section will explain the various domain and forest functional levels and point out which new features are available at each level.

Windows 2000 Mixed Domain Functional Level

The Windows 2000 Mixed Domain Functional level provides for backwards -compatibility with a Windows 2000 Active Directory running in Mixed mode. Installed at this level, Windows Server 2003 domain controllers will be able to communicate with both Windows NT 4.0 and Windows 2000 domain controllers throughout the forest. At this level, Windows Server 2003 shares the same limitations present in the Windows 2000 Mixed mode domain.

Windows Server 2003 servers in the Mixed mode domain and forest levels can take advantage of installing Active Directory from Media. This feature will be discussed in the next section.

Windows 2000 Native Functional Level

The Windows 2000 Native Functional Level is the initial operating level of Windows Server 2003 domain controllers installed into a Windows 2000 Native mode domain. At this level there are no NT 4.0 domain controllers. All authentication is performed by Windows 2000 and Windows Server 2003 domain controllers.

At this level, Active Directory can use Universal Groups and Windows Server 2003 domain controllers can cache Universal Groups. These features are discussed in following sections.

Windows Server 2003 Interim Functional Level

The Windows Server 2003 Interim Functional Level is the initial operating level of Windows Server 2003 domain controllers installed into a Windows NT 4.0 domain. This level is provided primarily as a stepping stone during a migration from Windows NT 4.0 to Windows Server 2003. The Interim Functional level comes into play for those companies that have not upgraded to Windows 2000, but instead migrate directly to Windows Server 2003 Active Directory.

Windows Server 2003 Functional Level

To gain the full functionality of a Windows Server 2003 Active Directory, the Windows Server 2003 Functional Level is the final goal for domain and forest functional levels. Functionality at this level enables many of the new features available to Windows Server 2003, such as renaming domains and domain controllers, schema deactivation , and cross-forest trusts. In order for you to promote your Active Directory to the full Windows Server 2003 Functional level, all domain controllers must be upgraded to Windows Server 2003. Individual domains can be promoted to the Windows Server 2003 functional level, but the forest can only be promoted to this functional level after all the domains in the forest are operating at this highest level.

At this level, Active Directory can benefit from all the new Windows Server 2003 features, including domain rename, cross-forest trusts, schema deletes, partial global catalog synchronization, and linked-value replication. All these new Active Directory features are discussed in the following sections.