nslookup(1) nslookup(1)NAME nslookup - query name servers interactively SYNOPSIS nslookup nslookup - server nslookup host-to-find [server] DESCRIPTION nslookup is a program which queries DARPA Internet domain name servers. server is a either the host name or address for a name server. 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. 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 server. INTERACTIVE COMMANDS Commands may be interrupted at any time by typing a CONTROL-C. To exit, enter the end-of-file signal, CONTROL- D. 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 April, 1990 1
nslookup(1) nslookup(1)initial server to look up information about domain while server uses the current default server. If an au- thoritative 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 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 ad- dresses. 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 re- ceived 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: 2 April, 1990
nslookup(1) nslookup(1)all Prints the current values of the various options to set. Information about the current default server and host is also printed. April, 1990 3
nslookup(1) nslookup(1)[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 de- fault domain name is appended to all lookup re- quests 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: A the host's Internet address (the de- fault). CNAME the canonical name for an alias. HINFO the host CPU and operating system type. MD the mail destination. MX the mail exchanger. MG the mail group member. MINFO the mailbox or mail list information. MR the 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 re- quest is resent. The retry value controls how many times a request is resent before giving up. 4 April, 1990
nslookup(1) nslookup(1)(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 re- ply 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) ⊕ 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 deter- mine 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 infor- mation 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, type the host name. To request a listing of hosts April, 1990 5
nslookup(1) nslookup(1)in the UCLA domain, use the ls command. The ls command requires a domain name (in this case, ucla.edu) as an ar- gument. Note that if you are connected with a name server that han- dles more than one domain, all lookups for host name 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 value 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 oc- curs 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. 6 April, 1990
nslookup(1) nslookup(1)Format error The name server found that the request packet was not in the proper format. This error should not occur. It would indicate a bug in the program. FILES /etc/bind/tools/nslookup /etc/resolv.conf initial domain name and name server addresses SEE ALSO named(1M), resolver(4). RFC-882, RFC-883 (DNN Network Information Center, SRI Inter- national) April, 1990 7