nslookup(1C)

NAME

nslookup − query name servers interactively

SYNOPSIS

nslookup [ host-to-find | − [ server address | server name ]]

DESCRIPTION

Nslookup is a program to query DARPA Internet domain name servers. Nslookup has two modes: interactive and non-interactive. Interactive mode allows the user to query the name server for information about various hosts and domains or print a list of hosts in the domain. Non-interactive mode is used to print just the name and Internet address of a host or domain.

ARGUMENTS

Interactive mode is entered in the following cases:

a)when no arguments are given (the default name server will be used), and

b)when the first argument is a hyphen (−) and the second argument is the host name of a name server.

Non-interactive mode is used when the name of the host to be looked up is given as the first argument. The optional second argument specifies a name server.

INTERACTIVE COMMANDS

Commands may be interrupted at any time by typing a control-C. To exit, type a control-D (EOF). The command line length must be less than 80 characters. N.B. an unrecognized command will be interpreted as a host name.

host [server]
Look up information for host using the current default server or using server if it is specified.

server domain

lserver domain
Change the default server to domain. Lserver uses the initial server to look up information about domain while server uses the current default server. If an authoritative answer can’t be found, the names of servers that might have the answer are returned.

rootChanges the default server to the server for the root of the domain name space. Currently, the host sri-nic.arpa is used. (This command is a synonym for the lserver sri-nic.arpa.) The name of the root server can be changed with the set root command.

finger [name] [> filename]

finger [name] [>> filename]
Connects with the finger server on the current host. The current host is defined when a previous lookup for a host was successful and returned address information (see the set querytype=A command). Name is optional. > and >> can be used to redirect output in the usual manner.

ls domain [> filename]

ls domain [>> filename]

ls -a domain [> filename]

ls -a domain [>> filename]

ls -h domain [> filename]

ls -h domain [>> filename]
List the information available for domain. The default output contains host names and their Internet addresses. The -a option lists aliases of hosts in the domain. The -h option lists CPU and operating system information for the domain. When output is directed to a file, hash marks are printed for every 50 records received from the server.

view filename
Sorts and lists the output of the ls command with more(1).

help

?Prints a brief summary of commands.

set keyword[=value]
This command is used to change state information that affects the lookups. Valid keywords are:

allPrints the current values of the various options to set. Information about the current default server and host is also printed.

[no]debug
Turn debugging mode on. A lot more information is printed about the packet sent to the server and the resulting answer.
(Default = nodebug, abbreviation = [no]deb)

[no]defname
Append the default domain name to every lookup.
(Default = nodefname, abbreviation = [no]def)

domain=name
Change the default domain name to name. The default domain name is appended to all lookup requests if the defname option has been set.
(Default = value in /etc/resolv.conf, abbreviation = do)

querytype=value
Change the type of information returned from a query to one of:

Athe host’s Internet address (the default).

CNAMEthe canonical name for an alias.

HINFOthe host CPU and operating system type.

MDthe mail destination.

MXthe mail exchanger.

MGthe mail group member.

MINFOthe mailbox or mail list information.

MRthe mail rename domain name.

Other types specified in the RFC883 document are valid but aren’t very useful.
(Abbreviation = q)

[no]recurse
Tell the name server to query other servers if it does not have the information.
(Default = recurse, abbreviation = [no]rec)

retry=number
Set the number of retries to number. When a reply to a request is not received within a certain amount of time (changed with set timeout), the request is resent. The retry value controls how many times a request is resent before giving up.
(Default = 2, abbreviation = ret)

root=host
Change the name of the root server to host. This affects the root command.
(Default = sri-nic.arpa, abbreviation = ro)

timeout=number
Change the time-out interval for waiting for a reply to number seconds.
(Default = 10 seconds, abbreviation = t)

[no]vc
Always use a virtual circuit when sending requests to the server.
(Default = novc, abbreviation = [no]v)

TUTORIAL

The domain name space is tree-structured and currently has five top-level domains:

•COM (for commercial establishments),

•EDU (for educational institutions),

•GOV (for government agencies) and

•ORG (for not for profit orginizations)

•MIL (for MILNET hosts).

If you are looking for a specific host, you need to know something about the host’s organization in order to determine the top-level domain it belongs to. For instance, if you want to find the Internet address of a machine at UCLA, do the following:

a)Connect with the root server using the root command. The root server of the name space has knowledge of the top-level domains.

b)Since UCLA is a university, its domain name is ucla.edu. Connect with a server for the ucla.edu domain with the command server ucla.edu. The response will print the names of hosts that act as servers for the domain ucla.edu. Note that the root server does not have information about ucla.edu but knows the names and addresses of hosts that do. All future queries will be sent to the UCLA name server.

c)To request information about a particular host in the domain (e.g. locus), just type the host name. To request a listing of hosts in the UCLA domain, use the ls command. The ls command requires a domain name (in this case, ucla.edu) as an argument.

Note that if you are connected with a name server that handles more than one domain, all lookups for host names must be fully specified with its domain. For instance, the domain harvard.edu is served by seismo.css.gov, which also services the css.gov and cornell.edu domains. A lookup request for the host aiken in the harvard.edu domain must be specified as aiken.harvard.edu. However, the set domain=name and set defname commands can be used to automatically append a domain name to each request.

After a successful lookup of a host, use the finger command to see who is on the system or to finger a specific person. To get other information about the host, use the set querytype=value command to change the type of information desired and request another lookup. (Finger requires the type to be A.)

DIAGNOSTICS

If the lookup request was not successful, an error message is printed. Possible errors are:

Time-out
The server did not respond to a request after a certain amount of time (changed with set timeout=value) and a certain number of retries (changed with set retry=value).

No information
Depending on the query type set with the set querytype command, no information about the host was available, though the host name is valid.

Non-existent domain
The host or domain name does not exist.

Connection refused

Network is unreachable
The connection to the name or finger server could not be made at the current time. This error commonly occurs with finger requests.

Server failure
The name server found an internal inconsistency in its database and could not return a valid answer.

Refused
The name server refused to service the request.

The following error should not occur and it indicates a bug in the program.

Format error
The name server found that the request packet was not in the proper format.

FILES

/etc/resolv.confinitial domain name and name server addresses.

Museum

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