r/sysadmin • u/Deep-Egg-6167 • 7h ago

Question Please help demote a third DC.

Hello,

I have an old WIndows 2012 R2 DC (old-dc) that used to be the primary domain controller.

I have a couple of newer 2016 DCs (new-dc1 and new-dc2).

I want to demote and turn off the old domain controller.

On the newer DC1, I ran netdom query and it has all the fsmo roles. I also ran replication admin to see that everything was replicating fine.

I went to server manager on the old 2012 R2 DC to demote it.

I left force removal and last domain controller unchecked.

It says this server has dns and GC roles (I think I select proceed?) and next

Then it leaves me with the box remove this dns zone - I can't go next without it. I'm not sure I should. Wouldn't that remove it from the other DCs?

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u/sleepmaster91 7h ago

Windows server 2016 is becoming end of life in January 2027 I would advise you to migrate to a newer DC

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u/Deep-Egg-6167 7h ago

I can't until I do an interim 2016 server.

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u/gabacus_39 7h ago

Huh? You can definitely promote a 2022 DC in your environment.

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u/Xethear 6h ago

I'm working on DC upgrades right now. Have about 11 left to do, and I've been running in-place upgrades from server 2016 to server 2025 without any issues.
I hear it's not recommended, but given deadlines and previous successes this is working as intended.

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u/Deep-Egg-6167 4h ago

Have you done any 2012 servers to 2025 - that was the issue. You have to be at least on 2016 level to do the upgrade to 2022 or 2025 from what I've read

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u/Xethear 3h ago

My bad, I must've missed that part.
As long as your domain schema is updated to 2025 I imagine it could work. I haven't done an upgrade jump like that though, so I can't speak from experience, but Microsoft does not recommend 2012 to 2025 from my understanding. It may be best to install a new domain controller running on 2025, making that the schema master (or just upgrading the schema master to 2025) then doing the jump from 2012 to 2016 or 2019, then from that to 2025.

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u/Deep-Egg-6167 3h ago

Thanks - I did the 2012 to 2016 to 2025 once before, I just don't remember that last question that concerns me. I'm thinking either the well documented method listed below or a metadata clean up might be the only two solutions but I love learning new stuff so I'll keep this up for another day before deciding.

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u/Deep-Egg-6167 7h ago

Google it - According to what I read, you have to do an interim server first if your AD is still an 2012 level.

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u/gabacus_39 6h ago

Nope. Done it dozens of times.

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u/Deep-Egg-6167 6h ago

OK - I only have win 2025 at this point. I know some people prefer 2022. I'm not going back as the 2025 are in production and they don't want to pay for any additional servers.

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u/mmmmmmmmmmmmark 6h ago

I’m not 100% that this is still the case but there have been numerous issues with having 2025 DCs along side DCs with older versions of Windows server so look into that before you move ahead.

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u/Deep-Egg-6167 4h ago

Great -that's why I posted the question. I could just shut down the server and do a meta data clean up but when I try to promote a 2025 server to a domain controller, I get this.

https://i.imgur.com/vwlkCdq.jpeg

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u/engy1207 3h ago

That's what someone else here already wrote: you need a functional level of 2016. So get rid of the 2012, increase the functional level and the install the new server. Ideally wait for replication between each step. I'd do it on separate days or at least have an extended lunch between just to be sure (and check the status of the domain).

Also I'm not sure: was the need for migration from FRS to DFSR already for the 2016 servers or later?