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Linux Unix Network Administration  «Prev  Next»
Lesson 4 Basic nslookup operation
Objective Explain the Basic Use of the nslookup Program.
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.