The Netlogon service on the DC registers a number of records in DNS that enable other DCs and computers to find Active Directory-related information. If the DC is pointing to the Internet service provider's (ISP) DNS server, Netlogon does not register the correct records for Active Directory, and errors are generated in Event Viewer. The preferred DNS setting for the DC is itself; no other DNS servers should be listed. The only exception to this rule is with additional DCs. Additional DCs in the domain must point to the first DC (which runs DNS) that was installed in the domain and then to themselves as secondary.