Commands Reference, Volume 4

nslookup Command

Purpose

Queries Internet domain name servers.

Syntax

nslookup [ -Option ... ] [ Host ] [ -NameServer ]

Description

The nslookup command queries Internet domain name servers in two modes. Interactive mode allows you to query name servers for information about various hosts and domains, or to print a list of the hosts in a domain. In noninteractive mode, the names and requested information are printed for a specified host or domain.

The nslookup command enters interactive mode when no arguments are given, or when the first argument is a - (minus sign) and the second argument is the host name or Internet address of a name server. When no arguments are given, the command queries the default name server. The - (minus sign) invokes an optional subcommand (-Option... variable). With the exception of the set command, these subcommands are specified on the command line and must precede the nslookup command arguments. The set subcommand options can alternatively be specified in the .nslookuprc file in the user's home directory.

The nslookup command executes in noninteractive mode when the first argument is the name or Internet address of the host being searched for. In this case, the host name or Internet address of the name server is optional.

The noninteractive command looks up information for the specified Host using the default name server or the name server specified by the NameServer parameter. If the Host parameter specifies an Internet address and the query type is A or PTR, the name of the host is returned. If the Host parameter specifies a name and the name does not have a trailing period, the default domain name is appended to the name. To look up a host not in the current domain, append a single period to the name.

Note: If they are specified in the .nslookuprc file of the user's home directory, the set subcommand's domain, srchlist, defname, and search options can affect the behavior of the noninteractive command.

Subcommands

The following commands can be interrupted at any time by entering a Ctrl-C key sequence. To exit, enter a Ctrl-D key sequence or type exit. To treat a built-in command as a host name, precede it with an escape character, which is a \. Unrecognized commands are interpreted as host names.

The following subcommands are recognized by the nslookup command:

finger [Name] [> FileName] finger [Name] [>> FileName]	Connects with the finger daemon server on the current host. The current host is defined when a previous lookup for a host was successful and returned address information, such as that returned with the set querytype=A command. The Name parameter, which specifies a user name, is optional. The > and >> characters can be used to redirect output to a new or existing file.
server Domain lserver Domain	Changes the default server to the value specified by the Domain parameter. The lserver subcommand uses the initial server to look up information about the domain. The server subcommand uses the current default server. If an authoritative answer cannot be found, the names of any additional 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 `ns.nic.ddn.mil` is used. The name of the root server can be changed with the set root subcommand. (The root subcommand is synonymous with the lserver ns.nic.ddn.mil subcommand.)
ls [Option] Domain [> FileName] ls [Option] Domain [>> FileName]	Lists the information available for the Domain specified, optionally creating or appending the output to the file specified by the FileName parameter. The default output contains host names and their Internet addresses. Possible values for the Option parameter are: -t QueryType Lists all records of the specified type. The default record type is A. Valid types are: A Host's Internet address CNAME Canonical name for an alias HINFO Host CPU and operating system type KEY Security Key Record MINFO Mailbox or mail list information MX Mail exchanger NS Nameserver for the named zone PTR Host name if the query is an Internet address; otherwise, the pointer to other information SIG Signature Record SOA Domain's "start-of-authority" information TXT Text information UINFO User information WKS Supported well-known services -a Lists aliases of hosts in the domain (synonymous with the -t CNAME option). -d Lists all records for the domain (synonymous with the -t ANY option). -h Lists CPU and operating system information for the domain (synonymous with the -t HINFO option). -s Lists well-known services of hosts in the domain (synonymous with the -t WKS option). Note: When output is redirected to a file, hash marks are printed for every 50 records received from the server.
view FileName	Sorts the output of previous ls commands and lists them using the more command.
help
?	Prints a brief summary of commands.
exit	Exits the program.
set Keyword[=Value]	Changes state information that affects lookups. This subcommand can be specified on the command line or optionally included in the .nslookuprc file in the user's home directory. Valid keywords are: all Prints the current values of the frequently used options to set. Information about the current default server and host is also printed. class=Value Changes the query class to one of the following. The class specifies the protocol group of the information. The default is IN. IN Internet class CHAOS Chaos class HESIOD MIT Althena Hesiod class ANY Wildcard (any of the above) [no]debug Turns debugging mode on. The default is nodebug (off). [no]d2 Turns comprehensive debugging on. The default is nod2 (off). domain=Name Changes the default domain name to the name specified by the Name parameter. The default domain name is appended to a lookup request, depending on the state of the defname and search options. The domain search list contains the parents of the default domain if the search list has at least two components in its name. For example, if the default domain is `CC.Berkeley.EDU`, the search list is `CC.Berkeley.EDU` and `Berkeley.EDU`. Use the set srchlist command to specify a different list. Use the set all command to display the list. The default of the domain=Name option is the value specified in the system's hostname, /etc/resolv.conf, or LOCALDOMAIN file. srchlst=Name1/Name2/... Changes the default domain name to the name specified by the Name1 parameter, and changes the domain search list to the names specified by the Name1, Name2,..., parameters. A maximum of six names separated by slashes can be specified. Use the set all command to display the list of names. The default values are specified in the system's hostname, /etc/resolv.conf, or LOCALDOMAIN file. Note: This command overrides the default domain name and search list of the set domain command option. [no]defname Appends the default domain name to a single component lookup request (one that does not include a period). The default is defname (append). [no]search Appends the domain names in the domain search list to the request until an answer is received, if the lookup request contains a period other than a trailing period. The default is search. port=Value Changes the default TCP/UDP nameserver port to the number specified by the Value parameter. The default value is 53. querytype=Value
type=Value	Changes the information query to one of the following values. The default is A. A Host's Internet address ANY Any of the options available. CNAME Canonical name for an alias HINFO Host CPU and operating system type KEY Security Key Record MINFO Mailbox or mail list information MX Mail exchanger NS Name server for the named zone PTR Host name if the query is an Internet address; otherwise, the pointer to other information SIG Signature Record SOA Domain's "start-of-authority" information TXT Text information UINFO User information WKS Supported well-known services [no]recurse Tells the name server to query other servers if it does not have information. The default is recurse. retry=Number Sets the number of times a request is retried to the value specified by the Number parameter. When a reply to a request is not received within the time frame specified by the set timeout command, the timeout period is doubled and the request resent. This subcommand controls the number of times a request is sent before timing out. The default value is 4. root=Host Changes the name of the root server to the name specified by the Host parameter. The default is `ns.nic.ddn.mil`. timeout=Number Changes the initial time-out interval for waiting for a reply to the number of seconds specified by the Number parameter. The default value is 5 seconds. [no]vc Uses a virtual circuit when sending requests to the server. The default is novc (no virtual circuit). [no]ignoretc Ignores packet truncation errors. The default is noignoretc (do not ignore).

Examples

To change the default query type to host information (HINFO) and the initial time-out to 10 seconds, enter:
```
nslookup -query=hinfo -timeout=10
```

To set the domain and the search list to three names, lcs.MIT.EDU, ai.MIT.EDU, and MIT.EDU, enter:
```
nslookup -set srchlist=lcs.MIT.EDU/ai.MIT.EDU/MIT.EDU
```
This command overrides the default domain name and search list of the set domain command. Use the set all command to display the list.

To determine whether a name specifies a host, domain, or other entity, enter:

nslookup -querytype=ANY austin.ibm.com

The nslookup command returns all available information about the name austin.ibm.com, including Statement of Authority (SOA), name server, mail exchanger, and host Internet address information, as follows:

Server: benames.austin.ibm.com
Address: 9.3.199.2

austin.ibm.com origin = ausname1.austin.ibm.com
        mail addr = brian.chriss.austin.ibm.com
        serial=1993081210,refresh=3600,retry=300,expire=604800, min=86400
austin.ibm.com  nameserver = ausname1.austin.ibm.com
austin.ibm.com  nameserver = bb3names.austin.ibm.com
austin.ibm.com  nameserver = benames.austin.ibm.com
austin.ibm.com  nameserver = b45names.austin.ibm.com
austin.ibm.com  nameserver = bbcnames.austin.ibm.com
austin.ibm.com  nameserver = netmail.austin.ibm.com
austin.ibm.com  preference = 10, mail exchanger = netmail.austin.ibm.com
austin.ibm.com  inet address = 129.35.208.98
ausname1.austin.ibm.com  inet address = 129.35.17.2
bb3names.austin.ibm.com  inet address = 129.35.208.99
benames.austin.ibm.com   inet address = 9.3.199.2
b45names.austin.ibm.com  inet address = 129.35.49.2
bbcnames.austin.ibm.com  inet address = 129.35.17.68
netmail.austin.ibm.com   inet address = 129.35.208.98

To perform a noninteractive query on host opus, enter:
```
nslookup opus
```
The nslookup command responds similarly to the host command. The command returns the domain name and Internet address of host opus, as follows:
```
Name: opus.austin.ibm.com
Address: 129.35.129.223
```
If host opus had been a name server (a host running the named daemon with an empty /etc/resolv.conf file), the following information would have been displayed:
```
Server: loopback
Address: 0.0.0.0
```

Exit Status

When a lookup request is not successful, the nslookup command returns one of the following error messages:

Timed Out	Indicates the server did not respond to the request after the specified number of retries.
No Response from Server	Indicates that a name server is not running on the server machine.
No Records	Indicates the server does not have the resource records of the specified query type for the host, although the host name is valid.
Non-Existent Domain	Indicates the host or domain name does not exist.
Connection Refused	Indicates the connection to the name or finger server could not be made at the time of the inquiry. This error is typically associated with ls and finger requests.
Network Is Unreachable	Indicates the connection to the name or finger server could not be made at the time of the inquiry. This error is typically associated with ls and finger requests.
Server Failure	Indicates the name server encountered an internal inconsistency and could not return a valid answer.
Refused	Indicates the name server refused to service the request.
Format Error	Indicates the name server refused the request packet because it was not in the proper format.

Files

/usr/bin/nslookup	Contains the nslookup command.
/etc/resolv.conf	Contains the initial domain name and nameserver addresses.
$HOME/.nslookuprc	Contains the user's initial options.
HOSTALIASES	Contains the host aliases.
LOCALDOMAIN	Contains the override default domain.

Related Information

namerslv command, traceroute command.

named daemon.

res_query subroutine, res_search subroutine.

resolv.conf file format for TCP/IP.

TCP/IP Name Resolution in AIX 5L Version 5.2 System Management Guide: Communications and Networks.