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.


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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