Distributed Networks Distributed Networks






Linux Unix Network Administration  «Prev  Next»
Lesson 2 Basic nslookup operation
Objective Explain the basic use of the nslookup program.

Basic nslookup Operation

The nslookup program operates interactively. When you start the program from the UNIX command line, it uses the /etc/resolv.conf file to locate a name server, and initially directs its queries at that server.
$ nslookup
Default Server: dns.class.com
Address: 196.241.12.122
>
To look up the IP address of a host name, or the host name for an IP address, simply type the name or address to the prompt:
$ nslookup
Default Server: dns.class.com
Address: 196.241.12.122
> www.microsoft.com
Server: dns.class.com 
Address: 196.241.12.122
Name: www.microsoft.com
Addresses: 207.68.156.58, 207.68.156.61, 
207.46.130.14, 207.46.130.15,207.46.130.16, 
207.46.130.17, 207.46.130.138, 207.46.130.139,
207.46.130.149,207.46.130.150, 207.46.130.151,
207.46.130.164, 207.46.130.165, 207.46.131.13,
207.46.131.15, 207.46.131.16, 207.46.131.141,
207.68.137.53, 207.68.137.56, 207.68.137.59,
207.68.156.16, 207.68.156.49, 207.68.156.52
> 207.68.156.52
Server: dns.class.com 
Address: 196.241.12.122
Name:  www.microsoft.com
Address: 207.68.156.52


Evidently, Microsoft operates quite a few machines under the name www.microsoft.com.
You may see the phrase non-authoritative answer in the output from nslookup. This phrase means that nslookup obtained the information from a server cache, rather than by consulting an authoritative source such as an authoritative server or secondary server.
  1. authoritative server: A primary or secondary server for a zone is called an authoritative server when it obtains its information directly from data files describing the zone.
  2. secondary server: In addition to its primary server, a zone may have one or more secondary servers. A secondary server provides an alternative source for information on the zone.