Within a network there must be at least one machine acting as a NIS server. You can have multiple NIS servers, each serving different NIS "domains" - or you can have cooperating NIS servers, where one is the master NIS server, and all the other are so-called slave NIS servers (for a certain NIS "domain", that is!) - or you can have a mix of them...
Slave servers only have copies of the NIS databases and receive these copies from the master NIS server whenever changes are made to the master's databases. Depending on the number of machines in your network and the reliability of your network, you might decide to install one or more slave servers. Whenever a NIS server goes down or is too slow in responding to requests, a NIS client connected to that server will try to find one that is up or faster.
NIS databases are in so-called DBM format, derived from ASCII databases. For example, the files /etc/passwd and /etc/group can be directly converted to DBM format using ASCII-to-DBM translation software (makedbm, included with the server software). The master NIS server should have both, the ASCII databases and the DBM databases.
Slave servers will be notified of any change to the NIS maps, (via the yppush program), and automatically retrieve the necessary changes in order to synchronize their databases. NIS clients do not need to do this since they always talk to the NIS server to read the information stored in it's DBM databases.
Old ypbind versions do a broadcast to find a running NIS server. This is insecure, due the fact that anyone may install a NIS server and answer the broadcast queries. Newer Versions of ypbind (ypbind-3.3 or ypbind-mt) are able to get the server from a configuration file - thus no need to broadcast.
NIS+ is a new version of the network information nameservice from Sun. The biggest difference between NIS and NIS+ is that NIS+ has support for data encryption and authentication over secure RPC.
The naming model of NIS+ is based upon a tree structure. Each node in the tree corresponds to an NIS+ object, from which we have six types: directory, entry, group, link, table and private.
The NIS+ directory that forms the root of the NIS+ namespace is called the root directory. There are two special NIS+ directories: org_dir and groups_dir. The org_dir directory consists of all administration tables, such as passwd, hosts, and mail_aliases. The groups_dir directory consists of NIS+ group objects which are used for access control. The collection of org_dir, groups_dir and their parent directory is referred to as an NIS+ domain.