nslookup

nslookup is a network administration command-line tool available for many computer operating systems for querying the Domain Name System (DNS) to obtain domain name or IP address mapping or for any other specific DNS record.

Background

The name nslookup means name server lookup. Nslookup uses the operating system's local Domain Name System resolver library to perform its queries. Thus, it is configured automatically by the contents of the operating system file resolv.conf.^[1]

Even though the nslookup program is very old, its usage is still taught in computer courses such as the Cisco Networking Academy, and it is still installed by default on most versions of Windows including Windows XP, Windows Vista, and Windows 7.

Usage

nslookup operates in interactive or non-interactive mode. When used interactively, when the program is invoked without arguments (another option exists), the user issues parameter configurations or requests when presented the nslookup prompt ('>') in line by line fashion. In non-interactive mode parameters and the query are specified as command line arguments in the invocation of the program.

The general command syntax is:

 nslookup [-option] [name | -] [server]

Example

The following example queries the Domain Name System for the IP address of the domain name example.com by issuing the command nslookup example.com to the command line interpreter (shell):

$ nslookup example.com
Server:         192.168.0.254
Address:        192.168.0.254#53
 
Non-authoritative answer:
Name:   example.com
Address: 192.0.32.10

This is an example of interactive, prompted use of the nslookup application. The user executes the program without any arguments and issues parameters and queries at the program prompt ('>'):

 $ nslookup
 Default Server:  dsldevice.lan
 Address:  192.168.1.1
 
 > server 8.8.8.8
 Default Server:  google-public-dns-a.google.com
 Address:  8.8.8.8
 
 > set type=mx
 > wikipedia.org
 Server:  google-public-dns-a.google.com
 Address:  8.8.8.8
 
 Non-authoritative answer:
 wikipedia.org   MX preference = 10, mail exchanger = mchenry.wikimedia.org
 wikipedia.org   MX preference = 50, mail exchanger = lists.wikimedia.org
 > exit

In this example, the program first displays its default name server configuration, after which the user changes the name server to be used to the host at IP address 8.8.8.8. The type of query to be performed is specified by setting the type of record to be fetched (MX record). Finally, the user simply issues the domain name at the prompt to receive the query results. The command exit ends the interactive session and terminates the program.

See also

• Domain Information Groper (dig)
• whois
• host (Unix), a simple utility for performing Domain Name System lookups

References

1. ^ "DNS and BIND, Fourth Edition: Chapter 12. nslookup and dig". O'Reilly. http://docstore.mik.ua/orelly/networking_2ndEd/dns/ch12_01.htm. Retrieved 2010-07-20. 

External links

• Microsoft Windows
  • nslookup – Microsoft TechNet library
  • Using NSlookup.exe - Microsoft Knowledgebase
• Unix-like OSs
  • nslookup(1) – Linux User Commands Manual
• Other
  • DNS Web Tools at the Open Directory Project (includes web-version of nslookup)