Recently, I started building up a new test lab with Microsoft Server 2016. In this lab, I had the domain and forest functional level set to Server 2016. This was fine until a few days later, when I needed to test an application that was not supported for functional domains and forest levels greater than Server 2012R2. Rather than starting from scratch with this lab, I decided to test lowering the functional levels from Server 2016 to Server 2012R2. I was able to follow the steps in a TechNet article that referenced the same process for Server 2008R2 to Server 2008.
The first step is to open an Administrative Active Directory PowerShell, and yes it does need to be run as an Administrator.
Next, you should verify the current functional levels. It’s not absolutely necessary, but definitely a good idea.
Get-ADDomain | Format-Table Name , DomainMode
Get-ADForest | Format-Table Name , ForestMode
To raise the functional levels, use the following PowerShell commands one at a time and accept the confirmation.
Set-ADDomainMode –Identity domain.com –DomainMode Windows2012R2Domain
Set-ADForestMode –Identity domain.com –ForestMode Windows2012R2Forest
Now if you run the Get-ADDomain and Get-ADForest commands used earlier, you’ll see that the forest and domain both show functional levels of Server 2012R2.
It’s a straightforward process, but be aware of possible implications the change can have on other applications, etc. You should carefully evaluate this decision—just as you would when raising the functional levels.
Lucas Guth, Infrastructure Engineer, PEI