I'm working with a root and sub-domain setup and need to upgrade both domain and forest functional levels to at least Windows Server 2016. This is needed because I'm planning to replace some domain controllers. I've heard that you can't add a Windows Server 2025 DC if the forest level is below 2016. Currently, both of my domains are on Windows 2012 R2 and the forest is also on Windows 2012 R2. I'm considering the following upgrade order: 1) Upgrade the sub-domain DFL to Windows 2016 2) Upgrade the root domain DFL to Windows 2016 3) Upgrade the forest FFL to Windows 2016. I also have a few questions: 1) Can I perform a DFL and FFL raise on any DC server, or do I need a server with an FSMO role? 2) Is a domain admin account enough for raising the DFL in the tree domain? 3) Can the FFL be raised in the root domain using just an enterprise admin account? 4) Do I need to wait for replication between DFL and FFL raise operations since there are 20 DCs involved? 5) Lastly, how can I verify that the DFL and FFL operations were successful? Is there a specific Event ID to check?
2 Answers
For your upgrades, if all your servers are at least Server 2016, you can just proceed with raising the DFL and FFL without concerns. Your proposed upgrade order looks good! Just make sure you have the right permissions set up for each step. Also, raising the levels doesn't change or remove any existing features; it just unlocks new ones, which is helpful!
Yeah, you really should stay away from Windows Server 2025 for now; I've heard it has quite a few issues. Stick with 2022 if you can. As for your questions, you don't need an FSMO role holder to raise the DFL and FFL, and a domain admin account is typically sufficient for raising the DFL. For the FFL, an enterprise admin account works just fine. It's also a good idea to wait for replication between the raises, especially with a large number of DCs like you have – better to be safe than sorry!
What about verification? Is there a specific Event ID we should be looking for after the raises?
So, is it true that raising the DFL and FFL is a straightforward process? Can you really just go ahead and do it?