The three types of NIS systems are as follows:
Master server
Slave servers
Clients of NIS servers
Any system can be an NIS client, but only systems with disks should be NIS servers, either master or slave. Servers are also clients, typically of themselves.
NIS servers come in two varieties, master and slave. The system designated as master server contains the set of maps that the system administrator creates and updates as necessary. Each NIS domain must have one, and only one, master server, which can propagate NIS updates with the least performance degradation.
You can designate additional NIS servers in the domain as slave servers. A slave server has a complete copy of the NIS maps in the master server. Whenever maps in the master server are updated, the updates are propagated among the slave servers. Slave servers can handle any overflow of requests from the master server, minimizing "server unavailable" errors.
Normally, the system administrator designates one master server for all NIS maps. However, because each individual NIS map has the host name of the master server encoded within it, you could designate different servers to act as master and slave servers for different maps. To minimize confusion, designate a single server as the master for all the maps you create within a single domain. The examples in this chapter assume that one server is the master for all maps in the domain.
NIS clients run processes that request data from maps on the servers. Clients do not make a distinction between master and slave servers, since all NIS servers should have the same information.