Forest upgrades and functional levels

by Mitch Tulloch [Published on 12 April 2013 / Last Updated on 12 April 2013]

A tip on performing forest upgrades in Active Directory environments.

After upgrading your schema, you might want to raise your forest and domain functional levels. As a best practice, follow these practices:

  • Before changing your forest functional level, take at least one domain controller offline from each domain in your forest.
  • Before changing the domain functional level of any domain, take at least one domain controller offline from the domain.

In both cases, you should make sure that the domain controllers you take offline do not hold any flexible single master operations (FSMO) roles in the forest or domains.

Keep the domain controllers offline for 48 to 72 hours after changing functional levels; if no issues are found, you can return the offline domain controllers to service. If issues are discovered, however, you can use your offline domain controllers as the source for rebuilding servers if a rollback to a previous functional level is required.

This tip is excerpted from my latest book Training Guide: Installing and Configuring Windows Server 2012 from Microsoft Press.

Mitch Tulloch is an eight-time recipient of the Microsoft Most Valuable Professional (MVP) award and a widely recognized expert on Windows administration, deployment and virtualization.  For more information see http://www.mtit.com

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