Understanding AD DS Functional Levels

Understanding AD DS Functional Leve...

Updated: October 23, 2009

Applies To: Windows Server 2008, Windows Server 2008 R2

Functional levels determine the available Active Directory Domain Services (AD DS) domain or forest capabilities. They also determine which Windows Server operating systems that you can run on domain controllers in the domain or forest. However, functional levels do not affect which operating systems you can run on workstations and member servers that are joined to the domain or forest.

When you deploy AD DS, set the domain and forest functional levels to the highest value that your environment can support. This way, you can use as many AD DS features as possible. For example, if you are sure that you will never add domain controllers that run Windows Server 2003 to the domain or forest, select the Windows Server 2008 functional level during the deployment process. However, if you might retain or add domain controllers that run Windows Server 2003, select the Windows Server 2003 functional level.

Important
After you raise the domain or forest functional level, you cannot go back to a lower functional level.

When you deploy a new forest, you are prompted to set the forest functional level, and then set the domain functional level. You cannot set the domain functional level to a value that is lower than the forest functional level. For example, if you set the forest functional level to Windows Server 2008, you can set the domain functional level only to Windows Server 2008. The Windows 2000 native and Windows Server 2003 domain functional level values are not available on the Set domain functional level page of the Active Directory Domain Services Installation Wizard. In addition, all domains that you subsequently add to that forest have the Windows Server 2008 domain functional level by default.

The following sections describe the features that are available at the different functional levels.

Features that are available at domain functional levels

The following table shows the features that are available at each domain functional level.

Domain functional level	Available features	Supported domain controller operating systems
Windows 2000 native	All of the default AD DS features and the following directory features are available: Universal groups for both distribution and security groups. Group nesting Group conversion, which allows conversion between security and distribution groups Security identifier (SID) history	Windows 2000 Windows Server 2003 Windows Server 2008 Windows Server 2008 R2
Windows Server 2003	All the default AD DS features, all the features that are available at the Windows 2000 native domain functional level, and the following features are available: The domain management tool, Netdom.exe, which makes it possible for you to rename domain controllers Logon time stamp updates The lastLogonTimestamp attribute is updated with the last logon time of the user or computer. This attribute is replicated within the domain. The ability to set the userPassword attribute as the effective password on inetOrgPerson and user objects The ability to redirect Users and Computers containers By default, two well-known containers are provided for housing computer and user accounts, namely, cn=Computers,<domain root> and cn=Users,<domain root>. This feature allows the definition of a new, well-known location for these accounts. The ability for Authorization Manager to store its authorization policies in AD DS Constrained delegation Constrained delegation makes it possible for applications to take advantage of the secure delegation of user credentials by means of Kerberos-based authentication. You can restrict delegation to specific destination services only. Selective authentication Selective authentication makes it is possible for you to specify the users and groups from a trusted forest who are allowed to authenticate to resource servers in a trusting forest.	Windows Server 2003 Windows Server 2008 Windows Server 2008 R2
Windows Server 2008	All of the default AD DS features, all of the features from the Windows Server 2003 domain functional level, and the following features are available: Distributed File System (DFS) replication support for the Windows Server 2003 System Volume (SYSVOL) DFS replication support provides more robust and detailed replication of SYSVOL contents. Advanced Encryption Standard (AES 128 and AES 256) support for the Kerberos protocol Last Interactive Logon Information Last Interactive Logon Information displays the following information: The time of the last successful interactive logon for a user The name of the workstation that the used logged on from The number of failed logon attempts since the last logon Fine-grained password policies Fine-grained password policies make it possible for you to specify password and account lockout policies for users and global security groups in a domain. For more information, see Step-by-Step Guide for Fine-Grained Password and Account Lockout Policy Configuration (http://go.microsoft.com/fwlink/?LinkID=91477).	Windows Server 2008 Windows Server 2008 R2
Windows Server 2008 R2	All default Active Directory features, all features from the Windows Server 2008 domain functional level, plus the following features: Authentication mechanism assurance, which packages information about the type of logon method (smart card or user name/password) that is used to authenticate domain users inside each user’s Kerberos token. When this feature is enabled in a network environment that has deployed a federated identity management infrastructure, such as Active Directory Federation Services (AD FS), the information in the token can then be extracted whenever a user attempts to access any claims-aware application that has been developed to determine authorization based on a user’s logon method.	Windows Server 2008 R2

Features that are available at forest functional levels

The following table shows the features that are available at each forest functional level.

Forest functional level	Available features	Supported domain controllers
Windows 2000 native	All of the default AD DS features are available.	Windows Server 2008 R2 Windows Server 2008 Windows Server 2003 Windows 2000
Windows Server 2003	All of the default AD DS features, and the following features are available: Forest trust Domain rename Linked-value replication Linked-value replication makes it possible for you to change group membership to store and replicate values for individual members instead of replicating the entire membership as a single unit. Storing and replicating the values of individual members uses less network bandwidth and fewer processor cycles during replication, and prevents you from losing updates when you add or remove multiple members concurrently at different domain controllers. The ability to deploy a read-only domain controller (RODC) Improved Knowledge Consistency Checker (KCC) algorithms and scalability The intersite topology generator (ISTG) uses improved algorithms that scale to support forests with a greater number of sites than AD DS can support at the Windows 2000 forest functional level. The improved ISTG election algorithm is a less-intrusive mechanism for choosing the ISTG at the Windows 2000 forest functional level. The ability to create instances of the dynamic auxiliary class named dynamicObject in a domain directory partition The ability to convert an inetOrgPerson object instance into a User object instance, and to complete the conversion in the opposite direction The ability to create instances of new group types to support role-based authorization. These types are called application basic groups and LDAP query groups. Deactivation and redefinition of attributes and classes in the schema	Windows Server 2003 Windows Server 2008 Windows Server 2008 R2
Windows Server 2008	All of the features that are available at the Windows Server 2003 forest functional level, but no additional features are available. All domains that are subsequently added to the forest, however, operate at the Windows Server 2008 domain functional level by default.	Windows Server 2008 Windows Server 2008 R2
Windows Server 2008 R2	All of the features that are available at the Windows Server 2003 forest functional level, plus the following features: Active Directory Recycle Bin, which provides the ability to restore deleted objects in their entirety while AD DS is running. All domains that are subsequently added to the forest will operate at the Windows Server 2008 R2 domain functional level by default. If you plan to include only domain controllers that run Windows Server 2008 R2 in the entire forest, you might choose this forest functional level for administrative convenience. If you do, you will never have to raise the domain functional level for each domain that you create in the forest.	Windows Server 2008 R2

Guidelines for raising domain and forest functional levels

The following guidelines apply to raising the domain or forest functional levels:

You must be a member of the Domain Admins group to raise the domain functional level.
You must be a member of the Enterprise Admins group to raise the forest functional level.
You can raise the domain functional level on the primary domain controller (PDC) emulator operations master only. The AD DS administrative tools that you use to raise the domain functional level (the Active Directory Domains and Trusts snap-in and the Active Directory Users and Computers snap-in) automatically target the PDC emulator when you raise the domain functional level.
You can raise the forest functional level on the schema operations master only. Active Directory Domains and Trusts automatically targets the schema operations master when you raise the forest functional level.
You can raise the functional level of a domain only if all domain controllers in the domain run the version or versions of Windows that the new functional level supports.
You can raise the functional level of a forest only if all domain controllers in the forest run the version or versions of Windows Server operating system that the new functional level supports.
You cannot set the domain functional level to a value that is lower than the forest functional level.
You cannot lower the domain or forest functional level after you have raised it.
You cannot reverse the operation of raising the domain and forest functional levels. If you have to revert to a lower functional level, you must rebuild the domain or forest, or restore it from a backup copy.