Product Reviews

A Few of My Favorite Things: NSLookup

Compaq knows a thing or two about troubleshooting large networks. Here are some of the utilities and programs it uses most and likes best for Windows 2000.

• By Kendall Wright
• 08/01/2001

Many problems with Internet communications result from the inability to resolve a domain name to an IP address. NSLookup is a command-line utility designed for troubleshooting Domain Name Service (DNS) problems such as host name resolution. In Win2K, the utility is installed automatically with TCP/IP. NSLookup displays all types (“A” records, CNAME, PTR, MX and so on) and classes (IN, CS, CH and so on) of DNS resource records. By default, only Type A records are returned.

The utility can be used either interactively or non-interactively. To use nslookup interactively, type “nslookup” at the command prompt. From the nslookup prompt, type “help” or “?” for a list of supported commands. Non-interactive mode puts all commands on one line, preceding subcommands with a dash.

In interactive mode (see figure), the default server and its address are listed by the utility. Set the DNS server to one of Compaq’s public network nameservers to get Compaq’s view of its public network. Then set the “type” to “any,” to find all types of records for “compaq.com.” The returned data shows the domain’s nameservers, information about the DNS database on the primary nameserver, MX (mail exchanger) records for compaq.com and the Internet addresses for the nameservers and mail exchangers.

NSLookup can tell you a lot more than just a server's IP address. (Click image to view larger version.)

To see only the MX records for compaq.com, invoke nslookup with the subcommand preceded by a dash (-q=MX, setting the query type to MX records), followed by the DNS name you want to resolve and the server you want to utilize for that resolution.

One nifty trick to isolate problems is to use someone else’s DNS server to see if they can resolve a name your server can’t. To do this in interactive mode, run through the interactive session, looking up the domain whose server you’d like to use. Type:

server

Finally, enter the domain name you wish to resolve. If the other server can resolve the name, maybe the problem is with your DNS server. If not, perhaps the name is wrong or there may be a problem with that domain’s DNS server.