Posted by arlene

NIS stores important information for servers on a network in a central database. When important information is stored in a central location, management of the data becomes much easier. The network administrator can make the necessary changes to the maps on an NIS master server and let NIS take care of informing the affected slave servers on the network about the change. The NIS master server also works to authenticate users against its database. However, to provide a backup, slave servers on the network also keep copies of the same files maintained by the NIS master server. This redundancy enables users to keep working if an NIS master server is offline for a short period. The master/slave method also can be used to provide for load balancing so that the master NIS server does not become overloaded on a large network.

The kind of data that NIS can manage for Unix servers includes the standard /etc/password and /etc/group files. It also includes other important files containing data about remote file systems, other hosts on the network, and so on.

NIS Maps

When you initially set up NIS, important system files are converted into databases that are referred to as NIS maps. In addition to the typical, the following files also are candidates for NIS management:

• /etc/ethers—This file results in two NIS maps: ethers . byaddr and ethers. byname. The Revers Address Resolution (RARP) uses this information when resolving Ethernet hardware (MAC) addresses to IP addresses. Typically, this is used by diskless workstations that need to discover their assigned IP address (which might not be stored locally) during the boot sequence.
• /etc/networks—This file also results in the creation of two NIS maps: networks. byname and networks. byaddr. You probably can guess that these maps store information used to associate network names with IP network addresses.
• /etc/services—Only one NIS map is created from this file. It contains a list of network servic and the TCP and UDP ports associated with these service port numbers.
• /etc/protocols—Two NIS maps result from this file. The first is called protocols. byname and the second is called protocols .byaddr. These maps work similarly to the services maps, in that they act to cross-reference protocol numbers with the names of the protocols.
• /etc/netmasks—The NIS map created by this file is called netmasks . byaddr, and it is used to store the subnet masks for the network.
• /etc/hosts—This field also results in two NIS maps, hosts. byname and hosts .byaddr. The standard hosts file used in TCP/IP is almost an antique today but still has a few uses. These maps can be used to translate hostnames to IP addresses for computers. The Domain Name System (DNS) servers typically perform this function on most networks today.
• /etc/aliases—This file also results in two NIS maps. They are mail. aliases and mail. byadd r. These maps are used to define alias email addresses.

The ypserve daemon runs on a central server and manages the NIS maps created from the standard systems files. The ypbind daemon runs on workstations and is responsible for interacting with the ypserve daemon to satisfy user requests and information interchange.

In addition to these files, other files that can be used on most NIS implementations include the following:

• Shadow password files—A user authorization file that is not world-readable like the /etc/passwd file. Instead, only root can manage this file.
• bootparams—Specific parameters for booting computers on the network.
• netgroup—Used to define networkwide groups (as opposed to the /etc/group groups). This makes managing groups of users on the network a simpler task.

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