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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

TCP/IP Address Resolution Protocol Utility (arp) 1 2 3 4 5 TCP/IP DNS Registry Database Lookup Utility (whois/nicname)

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.

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.

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.

TCP/IP Address Resolution Protocol Utility (arp) 1 2 3 4 5 TCP/IP DNS Registry Database Lookup Utility (whois/nicname)