The Network Information Service, or NIS (originally called Yellow Pages or YP), is a client–server directory service protocol for distributing system configuration data such as user and host names between computers on a computer network.
Because British Telecom PLC owned the name "Yellow Pages" as a registered trademark in the United Kingdom for its paper-based, commercial telephone directory, Sun changed the name of its system to NIS, though all the commands and functions still start with "yp".
Administrators have the ability to configure NIS to serve password data to outside processes to authenticate users using various versions of the Unix crypt(3) hash algorithms.
The original NIS design was seen to have inherent limitations, especially in the areas of scalability and security, so other technologies have come to replace it.
However, some functions—such as the distribution of netmask information to clients, as well as the maintenance of e-mail aliases—may still be performed by NIS or LDAP.