Many small companies have a small network and they have limited IT staff or manage IT services to take care of their network. I have seen old network devices, application, plan for cleaning up but it’s been forgotten which creates a problem in the future. The worse part is when the company doesn’t have a strict policy, budget or just don’t want to change, so things just build up until it reaches to a dead end. The domain controller is very important part of the network, if it keeps up to date and removed the old controller, then it could cause major issues. Here is how to clean up an old domain controller. Make sure you have a good backup and primary domain controller is a good healthy state.
Open Active Directory Users and Computers
Select domain>Domain Controllers>on right side it will list your domain controllers on the right side panel. You will see DC Type GC (Global Catalog) and Read-Only, GC Domain Controller.
Right click on the domain controller you want to delete, select delete. You will see confirmation screen select Yes
Select the options to clean up when your old domain controller deletes
Then it’s going to have confirmation and list of operations, based on your selection, once check then click OK
If your domain controller is part of GC, you will see: “This Active Directory Domain Controller is a global catalog“, before you click Yes, make sure you have at least one Global Catalog domain controller.
That will remove your old domain controller, then clean up any other metadata left around. If you have multi sites, open Active Directory Sites and Services: Sites>Delete old site
You will get Confirm Subtree Deletion message, click yes if nothing else is on that site
Then check your primary domain controller health and logs, to make sure everything is fine. Keep your eyes open on any application/services that may have any issues, it should not, but just in case. That’s it