ServerBuddies Support Blog

Understanding the dig command

dig will let you perform any valid DNS query, the most common of which are A (the IP address), TXT (text annotations), MX (mail exchanges), and NS nameservers.

The command dig is a tool for querying DNS nameservers for information about host addresses, mail exchanges, nameservers, and related information.

This tool can be used from any Linux (Unix) or Macintosh OS X operating system. The most typical use of dig is to simply query a single host.

A quick way to just get the answer only is to run the following command:

Use the following command to get a list of all the mailservers for mt-example.com:

Use the following command to get a list of authoritative DNS servers for mt-example.com:

dig, or domain information groper, provides the ability to query any domain server for information about the domains it serves. It operates in both an interactive mode and a batch query mode.

Using dig is much like using host, in that in its simplest mode you enter just the command and the name to lookup.

However, dig is more verbose by default and presents a much wider array or information, though in a somewhat less readable form.

Just like host, it is possible to query your default system resolver, or you can query a name server specified on the command line. For example, I could query name server about the google.com domain.

Above, we have a large amount of information, though not all of it is generally useful to us. First is the version of dig, and the command line options we specified.

The comes some status information, including the NOERROR designator that indicates the name was retrieve without error. If the domain did not exist, or could not be queried, there would be an NXDOMAIN error or some other error. Next are the flags of the query.

In this case, we have one query and one answer which are contained in the QUESTION and ANSWER sections below it. The next two items inform us of the number of AUTHORITY and ADDITIONAL sections that follow. In this case, the authority section gives us the primary and secondary name servers for this domain, ns1.serverbuddies.com and ns2.serverbuddies.com, and the additional section provides the IP addresses of those name servers.

The last few lines give the time the query required, the server that was queried and the port on which it was queried, the time and date on which the query was made, and the size of the message received from the name server.

Like host, dig has a mode in which you can query all of the information available about the domain. This can be done by appending the ANY argument to the end of the command line. Furthermore, the options NS, MX, CNAME, etc. are also available and do just what you would expect.

Reference - for more please check - http://doxfer.com/Webmin/