Server 2012 R2 Domain Controllers at 2008 r2 functional level?

I'm looking to get rid of our Server 2008 R2 domain controllers and moving to one 2012 R2 Full Domain Controller, with a few 2012 R2 Core edition replica domain controllers.
Will I need to upgrade the functional level of domain controller/AD to 2012 R2? Or can it continue to function at 2008 R2 level until I make that switch?
I'm not sure if raising the functional level to 2012 R2 will have a adverse effect on the environment or if they would be any pre-requisites to carry that out, or if it's just a simple action.
garryshapeAsked:
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Thomas GrassiSystems AdministratorCommented:
Keep the functional level at 2008 until you switch over every thing to 2012.

I just upgraded from 2003 to 2012 and that's what I did had no problems with AD at all

Once all my 2003 DC's where demoted and removed I was able to raise my level.

HTH
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Will SzymkowskiSenior Solution ArchitectCommented:
Will I need to upgrade the functional level of domain controller/AD to 2012 R2? Or can it continue to function at 2008 R2 level until I make that switch?

You have no choice but to leave the functional level at 2008R2 until ALL of your 2008R2 DC's are out of the environment. Once they are all removed (2008R2) you can keep the funcitonal level the same or at this point you can raise it.

I'm not sure if raising the functional level to 2012 R2 will have a adverse effect on the environment or if they would be any pre-requisites to carry that out, or if it's just a simple action.

When you raise the functional level (domain/forest) this simply opens new features that are usable to the domain controllers only. This does not have any affect on the members servers or client directly.

Forest/Domain raises are one way and cannot be un-done. So you need to make sure that you have a Full System State backup in case something goes wrong.

However as long as your AD replication and overall health of the domain controllers are good there it typically nothing to worry about.

Some of the commands you can run are below...
repadmin /replsum
repadmin /showrepl
repadmin /bridgeheads
DCDiag /v

Will.
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garryshapeAuthor Commented:
ok great thank you
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