Name

nslookup − interactively query servers running BIND, or BIND and Hesiod together

Syntax

/usr/ucb/nslookup [ host ][ server ]
/usr/ucb/nslookup [ − ][ server ]

Description

The nslookup command queries the BIND/Hesiod servers. This command has two modes: interactive and non-interactive. Interactive mode allows you to query the BIND/Hesiod server for information about various hosts and domains. Non-interactive mode allows you to obtain just the name and Internet address of a host or domain.

Use interactive mode if you have no arguments to provide.  In this case, nslookup queries the default BIND/Hesiod server. To specify a BIND/Hesiod server to query, the first argument should be a dash (−) and the second argument should be the name of the server. 

Use non-interactive mode when the name of the host you are looking up is the first argument.  The optional second argument specifies a BIND/Hesiod server.  If you do not supply a second argument, the current BIND/Hesiod server is queried. 

To terminate the nslookup command from within interactive mode, press <CTRL/D>. To terminate only the current lookup activity, press <CTRL/C>.

Non-interactive Options

host [server]
The host option is the name of the host for which you are looking up information.  If you do not specify a server, the default server is queried.  You can specify the server by either name or IP address. 

−  [server]
The − option returns the name and IP address of the default server, or the server you specify.  It then places you in interactive mode.  If you do not specify a server, the default server is queried.  You can specify the server by either name or IP address. 

Interactive Options

The command line length must be less than 80 characters.  Any unrecognized command is interpreted as a host name.  The following are the standard options:

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

server server
Changes the default server to the server specified.  This option uses the current default server. 

lserver server
Changes the default server to the server specified.  This option uses the initial default server to look up information about the server specified. 

rootChanges the default server to the server for the root of the domain name space specified.  Currently, the host nic.ddn.mil is used. 

finger [ name ] [ > [ > ] file ]
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=value command.  The name field is optional; but if used, it specifies a user name.  You can use the > and >> options to redirect output to the file specified. 

ls [ −adhlmst ] domain [ > [ > ] file ]
Lists the information available for the domain specified.  The default output contains host names and their Internet addresses. 

−aLists aliases of hosts in the domain, CNAME entries. 

−dLists all entries in the domain. 

−hLists CPU and operating system information for the domain, HINFO entries. 

−lSame as −d. 

−mLists mail exchangers in the domain, MX entries. 

−sLists well known services in the domain, WKS entries. 

−tLists Hesiod text information, TXT entries. 

If you redirect the output to a file, hash marks are printed for every 50 records received from the server. 

view file
Sorts and lists the output of the ls command with the more command.

help or ?
Print a brief summary of the nslookup commands and options.

set keyword[=value]
Changes the set options that affect the lookups, except for keywords all and ALL which display information. Valid keywords are:

allPrints the current values of the options you can set, as well as information about the current default server. 

ALLPrints the current values of the options you can set, as well as information about the current default server.  In addition, the ALL option prints the server state information. 

[no]debugTurns on debugging mode.  Verbose information is printed about the packet sent to the server and the resulting answer. 

The default is nodebug , which you can abbreviate to [no]deb. 

[no]defname
Appends the default domain name to every lookup. The default is nodefname, which you can abbreviate to [no]def. 

[no]recurse
Tells the BIND/Hesiod server to query other servers if it does not have the information. The default is recurse, and the abbreviation is [no]rec. 

[no]vcUses a TCP connection when sending requests to the server.  The default is novc, and the abbreviation is [no]v. 

domain=name
Changes the default domain to the domain name specified.  The default domain name is appended to all lookup requests if the defname option is set.  The default value is set in the /etc/resolv.conf file, which you can abbreviate to do. 

class=value
Changes the class of information returned from a query to one of the following values:

INInternet (default)

HSHesiod

ANYany

The abbreviation for the class option is cl. 

querytype=value
Changes the type of information returned from a query to value.  The following is a list of the most common values:

Ahost Internet address (default)

CNAMEcanonical name for an alias

MXmail exchanger

NSname server

PTRhost Internet name

SOAStart of authority

TXTA Hesiod data query

WKSA well known service

The abbreviation for the querytype option is q. 

retry=number
Sets the number of retries to the number specified.  If 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 to be resent before giving up.  The default retry number is 2, and the abbreviation for the retry option is ret. 

root=hostChanges the name of the root server to the host name specified.  This affects the root command.  The default is nic.ddn.mil, and the abbreviation is ro. 

timeout=number
Changes the time-out interval for waiting for a reply to the number specified (in seconds).  The default is 10 seconds, and the abbreviation for the timeout option is t. 

Tutorial

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

•ARPA (for ARPAnet hosts) The ARPA domain is currently one of the top-level domains, but is being phased out.

•COM (for commercial establishments)

•EDU (for educational institutions)

•GOV (for government agencies)

•ORG (for not for profit organizations)

•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 host at UCLA, do the following:

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

2.Connect with a server for the ucla.edu domain. The domain name for UCLA, which is a university, is ucla.edu. To connect with this server, you can type:

# nslookup
>  server ucla.edu

The response is the names of the 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 are sent to the UCLA BIND server.

3.Request information about a particular host in the domain, for example, purple. To do this, type the host name. To request a list 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 BIND 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 novel in the harvard.edu domain must be specified as novel.harvard.edu. However, you can use the set domain=name and set defname commands 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 get information about  a specific person. To get other information about the host, use the set querytype=value command, which allows you to change the type of information obtained and request another lookup.  The finger command requires that the information requested information be of type A, a host Internet address.

Hesiod Tutorial

If you  have set up Hesiod on your ULTRIX system and would like to look at this information, you must use the set class=value and set querytype=value commands, where value is HS and TXT respectively.

The following example presumes that the networks database is set up to be distributed with BIND/Hesiod.  The answer received from the nslookup command is that 128.45 is the network number for the network named ethernet in the networks.dec.com domain.

# nslookup
Default Server:  localhost.dec.com
Address:  127.0.0.1
 > set cl=hs
> set q=txt
> ethernet.networks
Server:  localhost.dec.com
Address:  127.0.0.1
 ethernet.networks.dec.com  ethernet:128.45
>

Diagnostics

If the lookup request was not successful, the nslookup command displays one of the following error messages:

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, although the host name is valid. 

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

Connection refused
The connection to the BIND/Hesiod server was refused.

Network is unreachable
The connection to the BIND/Hesiod server cannot be made at the current time.

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

Refused
The BIND/Hesiod server refused to service the request.

Format error
The name server found that the request packet was not in the proper format. Contact your DIGITAL Field Service representative.

Files

/var/dss/namedb BIND server data file directory

/var/dss/namedb/named.boot
BIND server boot file

/var/dss/namedb/hosts.db
BIND primary server hosts file

/var/dss/namedb/hosts.rev
BIND primary server reverse address hosts file

/var/dss/namedb/named.local
BIND server local host reverse address host file

/var/dss/namedb/named.ca
BIND server cache file

/etc/resolv.conf
BIND data file

See Also

finger(1), more(1), nsquery(1), resolver(3), resolver(5), named(8)
Guide to the BIND/Hesiod Service