Functional Level Question

[Martstone]

Had 2 x 2012 servers, 2 domains with a trust relationship between the 2. Replaced one of the servers with a 2016 server (it says functional level is 2016) now anyone in the 2012 domain is unable to access resources in 2016 domain.... We think possibly because of functional level.

I guess I cant raise the 2012 to 2016 but i could take 2016 backwards to 2012, what are the implications? Is this a bad thing to do? Will my current 2016 domain be messed up?

Any advice as I have never messed with functional levels :-)

[Norphy]

You can upgrade the functional level of a domain but you can't downgrade it. Once it's been set, it can't be de-set

 

The functional level of a domain mostly controls what version of Windows a domain controller can run. However, it shouldn't affect trusts between two domains; I have a domain running at 2016 level and another running at 2008 R2 level and they're trusting one another quite happily. It may be worth re-creating your trust?

[HPlum78]

@Norphy since server 2012R2 you can roll forward and back the forest and domain functional levels, that said I don't know that this has caused the issue that the op is experiencing.

 

You could try rolling back using PS commands:-

set-adforestmode

set-addomainmode