The domain naming operations master role holder is responsible for adding domain controllers and removing domains controllers from the Active Directory forest. When you add or remove a domain controller for the forest, it will contact the domain naming operation master role holder via the Remote Procedure Call (RPC) connection, and if it fails, it will not allow you to add or remove the domain controller from the forest. This is a forest-wide role, and only one domain naming operations master role holder can exist in one forest.

In the Active Directory forest, the domain naming operations master role owner can be found using the following command:

Get-ADForest | select DomainNamingMaster