Forest functional level is the state of entire forest which when upgraded or raised provides some added features forest wide. Before raising forest functional level you need to be sure that all the domain controllers of all the domains in the entire forest are at least at the respective domain functional levels at which you are about to upgrade your forest functional level. For example if you want to raise your forest functional level to Windows server 2003 first of all you need to raise domain functional levels of all the domain controllers of all the domains of the forest to Windows server 2003 functional level. You can raise the forest functional level in Windows server 2003 by following the steps given below:
- Logon to the domain controller with administrator account.
- Click on Start button.
- From the start menu go to Administrative Tools and from the submenu click on Active Directory Domains and Trusts.
- From Active Directory Domains and Trusts snap-in right click on Active Directory Domains and Trusts node and from the context menu click on Raise Forest Functional Level.
- From Forest Functional Level box from the drop-down list choose the appropriate forest functional level as required and click on Raise button.
- On the confirmation box click on Ok button and on the message box again click on Ok button to accept and confirm your configuration.
- Close Active Directory Domains and Trusts snap-in.
Raising forest functional level is one-way process which cannot be reverted back. This means that if once the forest functional level is raised you cannot downgrade the functional level.