NAME

nslookup - query name servers interactively

SYNOPSIS

nslookup [ -l ] [ address ]

DESCRIPTION

nslookup is an interactive program to query ARPA 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/resolve.conf. (If /etc/resolve.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 four top-level domains at present:

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 server ucla.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.

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

To exit, type Ctrl-D (EOF).  The command line length must be
less  than  80  characters.  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.

view filename

Sort and list the output of the ls command with more(1).

help
?    Print a brief summary of commands.

set keyword [ = 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/resolve.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.

FILES

/etc/resolve.conf initial domain name and name server addresses.

SEE ALSO

named(1M), resolver(3N), resolve.conf(4), RFC 882, RFC 883.

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.