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Can we downgrade Domain functional level from Win2008 R2 to Win2008

We are planning on upgrading our Domain/Forest functional level from Windows 2003 to Windows 2008 R2.  I understand we cannot go back to Windows 2003 DFL once we upgrade to Win2008 R2, without going through the Forest Restore.  We have some older software that we need to continue to support and have verified with the vendor that this software will run OK if we upgrade straight from Win2003 DFL/FFL to Win2008 R2 DFL/FFL.  My question is, in spite of our discovery if we encounter some type of issue with one of these applications running in the Win2008 R2 DFL can we downgrade to Win2008 DFL/FFL?
Thank you,
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You can go from 2008 R2 to 2008 DFL.

There's actually a technet article on it here:

Newest member in the A-Team, Aman Sahota, gives us insights on some simple, yet important steps in Active Directory management.

In Windows Server 2008 R2 and Windows Server 2012, you can lower the Forest and Domain functional level from 2012 to 2008 R2, or from 2008 R2 to 2008. But you cannot lower it beyond 2008. Also, this is not possible by GUI, you have to use PowerShell for doing this. Let’s see how you can do it in the following steps:


Great article.  Thank  you for your assistance!