All servers running Windows-based services rely on the information stored in the Active Directory to function correctly. If you experience problems with domain controllers in the Windows Server domain, you must repair them immediately. If the problems occur, you might experience minor complications with your servers running Windows-based services, or these services might stop functioning.
To make sure one of the domain controllers is available at all times, make sure that you have more than one domain controller in each Active Directory domain. Therefore, if a single domain controller fails, the replicated Active Directory information is still available in the remaining domain controllers.