We're going to be upgrading our servers from Server 2003 SP1 to Server 2012 R2 soon (finally), but I wanted to doublecheck that once the Domain Controller is upgraded from 2003 SP1 OS to Server 2012 R2 OS at a 2012 R2 functional level, will the other Server 2003 SP1 machines still be able to join the domain and function properly for a while until they are upgraded as well?

I found this answer:

Join Windows 2003 R2 guest to Windows 2012 R2 domain controller

But it was asking about 2003 R2. I'm asking about the older 2003 Vanilla with Service Pack 1.

1 Answer 1


The forest and domain functional levels will prohibit only having Domain Controllers with a lesser OS. You can join 2003 Member Servers to a 2012 Domain Functional level. See here - AD DS Functional Levels

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