Raising the functional level has nothing to do with member server,even though DFL is windows 2008, you can still run member server of lower OS version(2000/2003) , that means once you have your DFL to windows 2008, you cant have dc's running on windows 2000 or 2003,so application dependent on them for authentication will not work, but i have never heard of any application.

So,if you have any doubt, you can test in a lab or take system state back up before raising the DFL.

DFL once raised can't be reverted back & it can only be reverted by  restoring to previous backup.

• Marked as answer by Nina Liu - MSFTModerator Monday, January 31, 2011 6:09 AM

Hello,

raising the functional levels have only effect on DCs, not on member servers. The only "risk" is that you can't go back to Windows server 2003 anymore.

To be sure create a lab with the major server roles you have or where you have thoughts it can result in trouble and test it there first, which btw. should be always done before doing such steps in production domains.

I will caution, you our SAN had to be upgraded prior to us pulling the plug and moving forward.  You should be able to bring up a virtual SAN to simulate your environment.  Also (Unrelated to AD but the o/s), check your backup and AV and verify that they are certified for 2008 R2, we have had a lot issues with vendors covering this.

--
Paul Bergson
MVP - Directory Services
MCITP: Enterprise Administrator
MCTS, MCT, MCSE, MCSA, Security+, BS CSci
2008, Vista, 2003, 2000 (Early Achiever), NT4
http://www.pbbergs.com    Twitter @pbbergs
http://blogs.dirteam.com/blogs/paulbergson

Please no e-mails, any questions should be posted in the NewsGroup. This
posting is provided "AS IS" with no warranties, and confers no rights.

The key thing is moving the FSMO roles to the 2008 R2 DCs, in particular the PDC emulator introduces new objects.  If you upgrade to Windows 2008 R2 domain/forest then you can't use 2003 DCs anymore.

Computer browser service is disabled by default in Windows 2008 R2

Backup software need to be verified as working with 2008 R2 as well.  Other than that there is minimumal risk

Transitioning a Windows 2003 Domain to Windows 2008 R2
http://networkadminkb.com/Shared%20Documents/Transitioning%20a%20Windows%202003%20Domain%20to%20Windows%202008%20R2.aspx

I will caution, you our SAN had to be upgraded prior to us pulling the plug and moving forward.  You should be able to bring up a virtual SAN to simulate your environment.  Also (Unrelated to AD but the o/s), check your backup and AV and verify that they are certified for 2008 R2, we have had a lot issues with vendors covering this.

--
Paul Bergson
MVP - Directory Services
MCITP: Enterprise Administrator
MCTS, MCT, MCSE, MCSA, Security+, BS CSci
2008, Vista, 2003, 2000 (Early Achiever), NT4
http://www.pbbergs.com    Twitter @pbbergs
http://blogs.dirteam.com/blogs/paulbergson

Please no e-mails, any questions should be posted in the NewsGroup. This
posting is provided "AS IS" with no warranties, and confers no rights.

Hi,

Do you need to restart any Domain Controllers or Exchange Servers after the Domain/Forest Functionality level from 2003 to 2008R2 ?

Hi,

Do you need to restart any Domain Controllers or Exchange Servers after the Domain/Forest Functionality level from 2003 to 20

Hi,

Do you need to restart any Domain Controllers or Exchange Servers after the Domain/Forest Functionality level from 2003 to 20

Thanks Branko, what about trasnferring or migrating the FRS into another Domain Controller ?

https://msdn.microsoft.com/en-us/library/windows/desktop/ff384840%28v=vs.85%29.aspx

because from that website it says that it is obs