Server for NIS can operate in a master mode or subordinate mode. (If Server for NIS is used in a domain, the master server in the domain must be Server for NIS.) In UNIX, the primary difference between the two is that both subordinate and master servers can read map data, while only the master server can update maps. Additionally, the master Network Information Service (NIS) server provides periodic updates of the maps to subordinate servers.

In the Windows environment running Server for NIS, because the data is stored in Active Directory Domain Services (AD DS), both master and subordinate servers share the same replicated AD DS database. This makes them peers as far as map updates or write access are concerned. Server for NIS in either master mode or subordinate mode allows updates to Network Information Service (NIS) map data stored in AD DS. Changes to AD DS on any of these servers are propagated to other computers running Server for NIS in the domain by the AD DS synchronization mechanism.

Although these servers operate as peers for data updates, there must still be only one master server for UNIX-based subordinate servers and clients. UNIX subordinate servers continue to receive map updates from the Windows-based domain controller running Server for NIS that is designated as the master server. Similarly, they will continue to send passwd changes only to the master server.

For information about changing a subordinate server to a master server, see Change a subordinate server to a master server.