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I am migrating our company's AD from a Windows SBS 2008 to a news Windows 2012 R2 Essentials server. Everything went fine and the new AD now is in production stage. The last step is adding an additional DC to the new domain for replica pourposes: I need to promote a Windows Server 2008 R2 that used to do the same in the old SBS domain.

The problem that arises when trying to use the dcpromo command is the following: "The Functional Level of the forest is incompatible with this operating system"

I understand that I need to lower the Active Directory domain/forest Functional Level from 2012/2012R2 to 2008 R2, but I would like to understand how this could affect the current domain (and the attached clients).

Thanks

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You'll need both the Domain Functional Level and the Forest Functional Level to be 2008 R2. To understand the differences, consult this page from Microsoft:

http://technet.microsoft.com/en-us/library/understanding-active-directory-functional-levels%28v=ws.10%29.aspx

You'll note that there's no difference between 2008 R2 and 2012 R2 FFL - so that should be a safe operation.

There are some minor differences between 2012 R2 and 2008 R2 DFL, however, and you'll need to research into those and ensure you're not relying on any of the features.

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  • Hello Dan, I just realized that I never thanked you (even though I had immediately accepted your answer).
    – kar.bon
    Nov 19, 2015 at 10:57

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