Chapter 8: Using nslookup

nslookup is a debugging tool provided as part of the BIND software package. It allows anyone to directlyquery a nameserver and retrieve any of the information known to the DNS system. It is helpful fordetermining if the server is running correctly and is properly configured, or for querying for informationprovided by remote servers.
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Chapter 8: Using nslookup [Chapter 8] 8.3 Configuring named The first time you run it, watch for error messages. named logs errors to the messages file. [11] Once named is running to your satisfaction, use nslookup to query the nameserver to make sure it is providing the correct information. [11] This file if found at /usr/adm/messages on both our Linux and Solaris sample systems but it might be located somewhere else on your system. Check your systems documentation. Previous: 8.2 Configuring TCP/IP Network Next: 8.4 Using nslookup the Resolver Administration 8.2 Configuring the Resolver Book Index 8.4 Using nslookup [ Library Home | DNS & BIND | TCP/IP | sendmail | sendmail Reference | Firewalls | Practical Security ]Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch08_03.htm (13 of 13) [2001-10-15 09:18:25] [Chapter 8] 8.4 Using nslookup Previous: 8.3 Configuring Chapter 8 Next: 8.5 Summary Configuring DNS Name named Service 8.4 Using nslookup nslookup is a debugging tool provided as part of the BIND software package. It allows anyone to directly query a nameserver 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. The nslookup program is used 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: % nslookup almond.nuts.com Server: peanut.nuts.com Address: 172.16.12.2 Name: almond.nuts.com Address: 172.16.12.1 Here, a user asks nslookup to provide the address of almond.nuts.com. nslookup displays the name and address of the server used to resolve the query, and then it displays the answer to the query. This is useful, but nslookup is more often used interactively. 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 CTRL-D (^D) or the exit command at the nslookup prompt. Redone in an interactive session, the previous query shown is: % nslookup Default Server: peanut.nuts.com Address: 172.16.12.2 > almond.nuts.com Server: peanut.nuts.com Address: 172.16.12.2 Name: almond.nuts.com Address: 172.16.12.1 > ^DPlease purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch08_04.htm (1 of 4) [2001-10-15 09:18:26] [Chapter 8] 8.4 Using nslookup By default, nslookup queries for A records, but you can use the set type command to change the query to another resource record type, or to the special query type ANY. ANY is used to retrieve all available resource records for the specified host. The following example checks MX records for almond and peanut. Note that once the query type is set to MX, it stays MX. It doesnt revert to the default A-type query. Another set type command is required to reset the query type. % nslookup Default Server: peanut.nuts.com Address: 172.16.12.2 > set type=MX > almond.nuts.com Server: peanut.nuts.com Address: 172.16.12.2 almond.nuts.com preference = 5, mail exchanger = almond.nuts.com almond.nuts.com inet address = 172.16.12.1 > peanut.nuts.com Server: peanut.nuts.com Address: 172.16.12.2 peanut.nuts.com preference = 5, mail exchanger = peanut.nuts.com peanut.nuts.com inet address = 172.16.12.2 > exit You can use the server command to control the server used to resolve queries. This is particularly useful for going directly to an authoritative server to check some information. The following example does just that. In fact, this example contains several interesting commands: q First we set type=NS and get the NS records for the zoo.edu domain. q From the information returned by this query, we select a server and use the server command to direct nslookup to use that server. q Next, using the set domain command, we set the default domain to zoo.edu. nslookup uses this default domain name to expand the hostnames in its queries, in the same way that the resolver uses the default domain name defined in resolv.conf. q We reset the query type to ANY. If the query type is not reset, nslookup still queries for NS records. q Finally, we query for information about the host tiger.zoo.edu. Because the default domain is set to zoo.edu, we simply enter tiger at the prompt. % nslookup Default Server: peanut.nuts.com Address: 172.16.12.2 > set type=NSPlease purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch08_04.htm (2 of 4) [2001-10-15 09:18:26] [Chapter 8] 8.4 Using nslookup > zoo.edu Server: peanut.nuts.com Address: 172.16.12.2 Non-authoritative answer: zoo.edu nameserver = NOC.ZOO.EDU zoo.edu nameserver = NI.ZOO.EDU zoo.edu nameserver = NAMESE ...