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Windows NT TCP/IP Network Administration by Robert Bruce Thompson, Craig Hunt

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Using nslookup

nslookup is a debugging tool provided with Windows NT 4.0. It allows anyone to directly query a name server and retrieve any of the information known to the DNS system. It is helpful for determining if the server is running correctly and is properly configured, or for querying for information provided by remote servers.

nslookup is used in the Windows NT command window to resolve queries either interactively or directly from the command line. Below is a command-line example of using nslookup to query for the IP address of a host:

C:\>nslookup www.fnc.gov
Server: thoth.ttgnet.com
Address: 172.16.12.1

Non-authoritative answer:
Name: www.fnc.gov
Address: 128.150.6.53

Here, a user asks nslookup to provide the address of www.fnc.gov. nslookup displays the name and address of the server used to resolve the query, and then it displays the answer to the query. Notice the “Non-authoritative” message in the response. thoth.ttgnet.com is our local server. This messages tells us that the local server retrieved this answer from its cache. As we’ll see shortly, when you need to do so, nslookup allows you to go directly to the remote authoritative server for an answer.

The real power of nslookup is seen in interactive mode. To enter interactive mode, type nslookup on the command line without any arguments. Terminate an interactive session by entering Control-C (^C) or the exit command at the nslookup prompt. Redone in an interactive session, the query shown earlier is:

C:\>nslookup ...

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