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Manual page for NSLOOKUP(8C)

nslookup - query domain name servers interactively

SYNOPSIS

nslookup [ -l ] [ address ]

DESCRIPTION

nslookup is an interactive program to query Internet domain name servers. The user can contact servers to request information about a specific host or print a list of hosts in the domain.

OPTIONS

-l: Use the local host's name server instead of the servers in /etc/resolv.conf. (If /etc/resolv.conf does not exist or does not contain server information, the -l option does not have any effect).
address: Use the name server on the host machine with the given Internet address.

USAGE

Overview

The Internet domain name-space is tree-structured, with top-level domains such as:

COM: commercial establishments
EDU: educational institutions
GOV: government agencies
MIL: 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:

Connect with the root server using the root command. The root server of the name space has knowledge of the top-level domains.
Since UCLA is a university, its domain name is ucla.edu. Connect with a server for the ucla.edu domain with the command serverucla.edu. The response will print the names of hosts that act as servers for that domain. Note: the root server does not have information about ucla.edu, but knows the names and addresses of hosts that do. Once located by the root server, all future queries will be sent to the UCLA name server.
To request information about a particular host in the domain (for instance, 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: 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.)

Commands

Commands may be interrupted at any time by typing CTRL-C. To exit, type CTRL-D (EOF). The command line length must be less than 80 characters. Note: 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.
root: Changes 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 `lserver sri-nic.arpa'.) The name of the root server can be changed with the set root command.
finger [ name]: Connect with the finger server on the current host, which is defined by a previous successful lookup for a host's address information (see the set querytype=A command). As with the shell, output can be redirected to a named file using > and >>.
"ls [-ah]: 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. As with the shell, output can be redirected to a named file using > and >>. When output is directed to a file, hash marks are printed for every 50 records received from the server.
viewfilename: Sort and list the output of the ls command with more.1
help
?: Print a brief summary of commands.
setkeyword [ = value ] This command is used to change state information that affects the lookups. Valid keywords are:

all: Prints the current values of the various options to set. Information about the current default server and host is also printed.
[no]deb[ug]: Turn debugging mode on. A lot more information is printed about the packet sent to the server and the resulting answer. The default is nodebug.
[no]def[name]: Append the default domain name to every lookup. The default is nodefname.
do[main]=filename: Change the default domain name to filename. The default domain name is appended to all lookup requests if defname option has been set. The default is the value in /etc/resolv.conf.
q[querytype]=value: Change the type of information returned from a query to one of:

A: The host's Internet address (the default).
CNAME: The canonical name for an alias.
HINFO: The host CPU and operating system type.
MD: The mail destination.
MX: The mail exchanger.
MB: The mailbox domain name.
MG: The mail group member.
MINFO: The mailbox or mail list information.

: (Other types specified in the RFC883 document are valid, but are not very useful.)
[no]recurse: Tell the name server to query other servers if it does not have the information. The default is recurse.
ret[ry]=count: Set the number of times to retry a request before giving up to count. When a reply to a request is not received within a certain amount of time (changed with set timeout), the request is resent. The default is count is 2.
ro[ot]=host: Change the name of the root server to host. This affects the root command. The default root server is sri-nic.arpa.
t[timeout]=interval: Change the time-out for a reply to interval seconds. The default interval is 10 seconds.
[no]v[c]: Always use a virtual circuit when sending requests to the server. The default is novc.

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.conf: initial domain name and name server addresses.