Network Information Service
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The Network Information Service or NIS (originally called Yellow Pages or YP) is Sun Microsystems’ client-server directory service protocol for distributing system configuration data such as user and host names between computers on a computer network.
Sun licenses this technology to virtually all other Unix vendors.
As the name “Yellow Pages” was a registered trademark in the United Kingdom of British Telecom PLC for their (paper) commercial telephone directory, Sun changed the name of their system to NIS, though all the commands and functions still start with “yp”.
NIS/YP is used for maintenance and distribution of a central directory of user and group information, hostnames, e-mail aliases and other text-based tables of information in a computer network. For example, in a common UNIX environment, the list of users for identification is placed in /etc/passwd, and secret authentication hashes in /etc/shadow. NIS adds another “global” user list which is used for identifying users on any client of the NIS domain.
Technically NIS can be configured to serve password data used to authenticate users against as well; however, not only is this cumbersome to do without resorting to DES encrypted passwords (which are known to be weak) if multiple OSs are in use, it also allows any NIS client to retrieve the whole password database for offline inspection. Kerberos was designed to handle authentication in a more secure manner.
In many environments other directory services, which may be considered to be more modern and secure than NIS, such as LDAP, have come to replace it. For example, the 'slapd' daemon generally runs as a non-root user, and SASL-based encryption of LDAP traffic is natively supported.
The nameserver functionality NIS or LDAP can provide is probably better handled by DNS servers when used on large LANs, leaving just site-wide identification information for NIS master and slave systems to serve. 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.
[edit] External links
- The NIS-HOWTO from the Linux Documentation Project
- Distributed Authentication System (DAS) Handbook by Van Emery
- NFS and NIS Security by Kristy Westphal - Securityfocus article Jan. 22, 2001
- Red Hat Linux 9: Red Hat Linux Security Guide - 5.3. Securing NIS
- Linux Focus: Yellow Pages - Includes some details on the underlying RPC calls
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