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TCP/IP DNS Name Resolution and Information Lookup Utilities (nslookup, host and dig)
(Page 2 of 5)
The nslookup Utility
To support all of these needs, modern
TCP/IP implementations come equipped with one or more DNS name resolution
and information lookup utilities. One of the most common DNS diagnostic
utilities is nslookup (“name server lookup”), which
has been around for many years. The details of how the program is implemented
of course depend on the operating system, though most of them are quite
similar in operation and settings. The utility can normally be used
in two modes: interactive or non-interactive.
Non-Interactive Use of nslookup
The non-interactive version of nslookup
is the simplest, and is most often used when an administrator wants
to just quickly translate a name into an address or vice-versa. It is
run by issuing the nslookup command using the following simple
syntax:
nslookup <host> [<server>]
Here, “<host>” can
be a DNS domain name, in which case a normal
resolution will be performed, or it may
be an IP address, which will cause nslookup to do a reverse
resolution to return the associated DNS
domain name. The “<server>” parameter is optional; if
omitted, the program uses the default name server of the host where
the command was issued. Table 290
shows a simple example of non-interactive use of nslookup.
Table 290: DNS Name Resolution Using the nslookup Utility
D:\aa>nslookup
www.pcguide.com
Server: ns1-mar.starband.com
Address: 148.78.249.200
Non-authoritative answer:
Name: pcguide.com
Address: 209.68.14.80
Aliases: www.pcguide.com
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This example was done on
my home PC that uses the Starband satellite Internet service; it is
configured to use Starband’s name server (“ns1-mar.starband.com”).
The answer provided here is labelled “non-authoritative” because
it came not from one of the DNS name servers that is a DNS
authority for www.pcguide.com, but rather
the Starband name server’s DNS
cache.
 Note: It is also possible to specify one or more options to modify the behavior of the lookup in non-interactive mode. These options are the same as the parameters controlled by the nslookup set command described in Table 291; they are specified by preceding them with a dash. For example, “nslookup -timeout=10 www.pcguide.com” would perform the same lookup as in Table 290 but with the timeout interval set to 10 seconds.
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