By definition, an NIS server is a machine storing a set of maps that are available to network machines and applications. The NIS server does not have to be the same machine as the NFS file server.
NIS servers come in two varieties, master and slave. The machine designated as master server contains the set of maps that you, the NIS administrator, create and update as necessary. Each NIS domain must have one, and only one, master server. This should be a machine that 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 master set of NIS maps. Whenever the master server maps are updated, the updates are propagated among the slave servers. The existence of slave servers allows the system administrator to evenly distribute the load resulting from answering NIS requests. It also minimizes the impact of a server becoming unavailable.
Normal practice is to designate one master server for all NIS maps. However, because each individual NIS map has the machine name of the master server encoded within it, you could designate different servers to act as master and slave servers for different maps. Note, however, that randomly designating a server as master of one map and another server as master of another map can cause a great deal of administrative confusion. For that reason it is best to have a single server be 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.