I am preparing to migrate our OLD 2003 Windows Server to a Windows 2012r2 Server. I have discovered we actually have a 2000 forest, not 2003. To put a Windows 2012r2 server member on the domain it must have a 2003 or greater forest.

So my question now is --- can I upgrade the active directory forest level from 2000 to 2003 while the domain is in use? Note: Nobody will be adding users or computers during this, just accessing the domain.

Of your I expect the answer is Yes but I have never done this before and my boss would not like it if I messed up our domain.

  • How would you do it when the domain is not in use though exactly? I think you just do as per the Microsoft best practices once you have a good backup of your domain controllers. We've always done these sort of changes late in the day in case there are issues it wouldn't have such a big impact while you work on reverting but we've never had issues when upgrading forest functional level from 2000 to 2003 that I recall so I think you'll be safe to proceed as long as you have a backup and follow the standards per Microsoft. – Pimp Juice IT Oct 28 '15 at 17:45

Active Directory does not have an "offline mode" or anything similar. All updates to the data or the schema are made live, and replicated accordingly. AD schema modifications are non-reversable, but I've never had any of Microsoft's schema updates cause a problem.


The answer is yes as you suspected, but that doesn't mean it can't go wrong.

As with any changes to AD make sure you have tested (I can't stress the word tested enough) backups, in case it does go wrong.

  • Of course we have studied this for years, and have a fool proof proven backup and restore that works at a press of a single button :-). We know everybody tests everything enough so we do to. – Ron Whites Oct 28 '15 at 19:34

Yes, you should be able to raise the functional level without interruptions to the end-users.

Might want to read up on the process from this page on Microsoft Support, "How to raise Active Directory domain and forest functional levels": https://support.microsoft.com/en-us/kb/322692


It should not disrupt services or user activity. I have never seen it break anything. There is no real reason to prohibit other AD activities, as the change is virtually instantaneous.

You will have to raise the domain functional level before raising the forest functional level.

There are new features available at each AD domain/forest level, so there is little reason to stay at a lower level unless you have DCs running that OS. E.g., if all of your DCs are 2008 R2 or higher, you should consider moving to that functional level.

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