HKLM\SYSTEM\CurrentControlSet\Services\
The Netlogon subkey stores information for the Net Logon service.
The Net Logon service verifies logon requests and registers, authenticates, and locates domain controllers. Also, to maintain backward compatibility, Net Logon manages replication of the user account database to backup domain controllers running Windows NT 4.0 and earlier.
For Windows 2000, Net Logon manages replication only when it involves servers running Windows NT 4.0 and earlier. Net Logon for Windows 2000 does not manage replication between two servers running Windows 2000.