What to check before upgrading the forest functional level

[thanhtien19]

Our system have active directory server 2012 r2 and forest functional level 2008 R2 and domain function 2008 R2 . Child domain functional level 2008 R2. Now we want upgrade functional level to 2012 r2 and after that to domain functional level . Please guide help me what to check before upgrade ? And can downgrade it have problem ?

[#2]

I'd check that the domain health is 100% before making any changes or upgrades. (dcdiag, repadmin tool)

[#3]

Just checking if there's any progress or updates?

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[#4]

do you need check another application Compatible as Exchange, Sharepoint....and OS ?

[#5]

Yes, I'd check them to be on the safe side.