What’s the safest way to move DHCP while replacing domain controllers?
Asked by
VelvetHarbor27
I'm migrating three domain controllers from Windows Server 2016 to 2022. Two of the existing domain controllers host DHCP in a failover load-balancing configuration. I'd like to move DHCP before replacing the domain controllers, while ultimately keeping the same hostnames and IP addresses for the replacements.
My proposed plan is to break the existing DHCP failover relationship, export the DHCP configuration to a temporary server, complete the domain controller migration, import the configuration onto the new primary server, and then recreate the failover relationship with the second new domain controller. Does that sequence make sense? This is a small environment with about 22 users and 30 servers, so I'm also considering whether DHCP should remain on the domain controllers at all.
Answers
If your firewall or network equipment supports reliable DHCP and can provide the same reservations, options, and failover behavior you need, that’s worth considering. Otherwise, two inexpensive VMs or small Server Core machines are a clean option. The important part is to treat the DHCP move as a separate change, test address assignment and renewals, and only then proceed with the domain controller cutover.
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That sequence is reasonable: remove the existing failover relationship, move the configuration to a temporary server, replace the domain controllers, import the scopes and settings onto the new primary server, and then configure failover with the second server.
Export the scopes, reservations, filters, and DHCP options, and pay attention to the existing leases. Test a client renewal before retiring the temporary server. Also make absolutely sure the old and new systems are never online with the same IP address at the same time. Keeping DHCP separate from the domain controller migration also gives you one less moving part during the cutover.
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This is also a good opportunity to move DHCP off the domain controllers permanently. DHCP can run on a firewall, managed network appliance, or a couple of small Server Core VMs. Even with only 22 users and around 30 servers, separating DHCP from AD DS reduces the number of services tied to a domain controller and makes future migrations easier.
VelvetHarbor27: I hadn’t planned to add dedicated DHCP servers, but moving it separately would make the replacement process simpler. I’m weighing that against keeping the current setup because the environment is small.
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VelvetHarbor27: That makes sense. I could also build two small Windows Server 2022 VMs specifically for DHCP, but I’m unsure whether that’s worthwhile in such a small environment.