ADC Domain Functional Level

Question

We had three DCs (one PDC - win 2019, one ADC - Wind 2012, and one ADC - Win2008). Now we have successfully demoted Windows 2008 ADC from the forest. Now we have left two DCs (Win 2019 where all FSMO roles are migrated and ADC). The functional level is still Windows 2008.
Now my question is can I raise the functional level to windows 2012? I am concerned that I have a few Windows 2008 member servers joined to this domain. If I raise the functional level, will it have an effect?

Answer 1

Yes, you can raise DFL to the level (2012) of lowest domain controller OS. The operating systems of member servers does not have any impact.

To activate the newest domain features, all the domain controllers must be running the newest Windows Server operating system version in the domain. If this requirement is met, the administrator can raise the domain functional level.

To activate the newest forest-wide features, all the domain controllers in the forest must be running the Windows Server operating system version that corresponds to the desired forest functional level. Additionally, the current domain functional level must already be at the newest level. If these requirements are met, the administrator can raise the forest functional level.
https://learn.microsoft.com/en-us/troubleshoot/windows-server/identity/raise-active-directory-domain-forest-functional-levels#summary

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Answer 2

Hello there,

Yes, you can raise the functional level, and here is why the forest functional level also dictates the minimum functional level at which all DCs in the forest should operate. Any DC that runs on a lower version of the Windows server will be demoted from the DC position. This restriction, however, is only applicable to DCs. Member servers and workstations in the forest will remain unaffected. So, the best practice is to raise the domain functional level first and then raise the forest functional level. Although, raising the forest functional level will automatically raise the domain functional level too.

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