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The TCP/IP Guide

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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP Administration and Troubleshooting Utilities and Protocols

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TCP/IP Address Resolution Protocol Utility (arp)
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TCP/IP DNS Registry Database Lookup Utility (whois/nicname)
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TCP/IP DNS Name Resolution and Information Lookup Utilities (nslookup, host and dig)
(Page 5 of 5)

The dig Utility

The second alternate to nslookup is dig, which stands for “Domain Information Groper” (likely a play on the supposed origin of the name “ping”). It differs from the host command in that it provides considerably more information about a domain, even when invoked in the simplest of ways. It is also quite a bit more complicated, with a large number of options, and features such as a batch mode for obtaining information about many domains.

The basic syntax for the dig command is different from nslookup or host, because if a non-default name server is specified, it is prepended with an at sign (“@”) and comes before the host to be looked up. A specific type of resource record can also be specified, like this:

dig [@<server>] <host> [<type>]

Table 294 shows the output from running dig on the same domain ( that I used as an example for nslookup and host. You can see that it provides much more information about the domain.

Table 294: DNS Name Resolution Using the dig Utility

; <<>> DiG 9.2.1 <<>>
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15912
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 0

; IN A



;; Query time: 1840 msec
;; WHEN: Tue Nov 18 16:05:08 2003
;; MSG SIZE rcvd: 109Server:

The dig command also allows specific types of resource records to be looked up, and includes dozens of options and settings. Since this topic is already getting very long and dig is by far the most advanced of the three utilities, I will stop here; consult your system’s documentation for the full instructions on how dig works and a list of its parameters.

Key Concept: Most TCP/IP implementations provide one or more utilities that can be employed by an administrator to manually resolve DNS domain names to IP addresses or perform related searches for DNS information. One of the most common is nslookup, which allows a host name to be translated to an address or vice-versa; it has both interactive and non-interactive modes. On some operating systems, nslookup has been replaced by the host utility for simple DNS lookups, and the dig program for more detailed inspections of DNS resource information.

On The Web: The dig utility is very useful, but has still not been implemented on some systems. Fortunately, there is an online dig utility you can access using your browser on the Internet. Find it at

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