How to use the nslookup command: 2-Minute Linux Tip

Hi, this is Sandra Henry-Stocker, author of the “Unix as a Second Language” blog on NetworkWorld.
In this Linux tip, we’re going to look at the nslookup command. nslookup will provide information on naming services and demonstrate how your system looks up hostnames prior to connecting to them.
It works with the name server that your system is configured to use as defined in the /etc/resolv.conf file. Let’s check it out …
In this response to this command, we see a lot of information:

A “non-authoritative answer” simply means that the name server you are communicating with has received this information from another name server. It is non-authoritative because it isn’t the source for this information.
You can also use nslookup to do what is called a “reverse lookup”. In other words, you start with an IP address and ask what system it belongs to. Let’s check the IP address we got in our earlier nslookup command:

Note that the bytes in the IP address are in reverse order. 10.42.178.108 => 108.178.42.10
To quit nslookup, type “exit”.
You can also use nslookup in a line-by-line mode. Provide an argument, get an answer and you’re back at the command prompt:
$ nslookup linuxqanda.org
109.178.42.10
$
That’s your Linux tip for today.
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