In the AIX Version 4.3.3 and later releases, the NIS-compatibility mode supports DNS forwarding. The main server is called the master server, and the backup servers are called replicas . At the time NIS was developed, it was assumed that most of the information NIS would store would be static. NIS updates are handled manually, and its maps have to be remade and propagated in full every time any information in the map changes. Changes must still be made to the master database on the master server, but once made, they are automatically propagated to the replica servers.
Propagation now takes only a matter of minutes.
For instance, the hosts table stores information about workstation addresses, while the passwd table stores information about users of the network. The master server stores the original tables, and the replicas store copies. The tables' information is loaded into memory as requests are made to the database. Keeping data in memory in the order requested minimizes calls to the disk, thereby improving request-response time. At the time NIS was developed, the type of information it stored would change infrequently, NIS was developed with an update model that focused on stability.