What is NSLookup?

This article applies to:

• Firewall Suite 4.X

Question:

Information:

NSLookup is a primary diagnostic tool for debugging a Domain Name System (DNS) architecture. You can use it to display any resource record on any DNS server including UNIX-based DNS implementations. NSLOOKUP from most other DNS implementations should also work against the Microsoft-based DNS server.

This is a command line utility and has the following syntax:

NSLOOKUP [[-option ...] [computer-to-find]] | - [server]

Modes:

NSLOOKUP has two modes: interactive and non-interactive.

• Non-Interactive Mode. If you only need to look up a single piece of data, use non-interactive mode. For the first argument, type the name or IP address of the computer to be looked up. For the second argument, type the name or IP address of a DNS name server. If you omit the second argument, the default DNS name server will be used.
• Interactive Mode. If you need to look up more than one piece of data, you can use interactive mode. Type a hyphen for the first argument and the name or IP address of a DNS name server for the second argument, or omit both arguments and the default DNS name server will be used. NSLookup provides a prompt. You can set options and search make multiple queries.
  

Parameters:

-option
You can specify one or more NSLOOKUP commands as a command-line option. For a list of commands, see below. For more details, enter HELP or ? in an interactive session.

Each option consists of a hyphen (-) followed immediately by the command name and, in some cases, an equal sign (=), and then a value. For example, to change the default query type to host (computer) information and the initial timeout to ten seconds, you would type:

NSLOOKUP -querytype=hinfo -timeout=10

The command line length must be less than 256 characters.

computer-to-find
This instruct NSLOOKUP to Look up information for computer-to-find using the current default server or using server if specified. If computer-to-find is an IP address and the query type is A or PTR, the name of the computer is returned. If computer-to-find is a name and does not have a trailing period, the default DNS domain name is appended to the name. (This behavior depends on the state of the set options: domains, srchlist, defname, and search.) To look up a computer not in the current DNS domain, append a period to the name.

If you type a hyphen (-) instead of computer-to-find, the command prompt changes to NSLOOKUP interactive mode.

server
Use this server as the DNS name server. If you omit server, the default DNS name server is used.

NSLOOKUP Commands:

For more details, enter HELP or ? in an interactive session.

• help
• exit
• finger
• ls
• lserver
• root
• server
• set
• set all
• set cl[ass]
• set [no]deb[ug]
• set [no]d2
• set [no]def[name]
• set do[main]
• set [no]ig[nore]
• set po[rt]
• set q[uerytype]
• set [no]rec[urse]
• set ret[ry]
• set ro[ot]
• set [no]sea[rch]
• set srchl[ist]
• set ti[meout]
• set ty[pe]
• set [no]v[c]
• view

Notes:

Firewall Suite does not perform the DNS lookup function itself. Instead, it seeks help from the network's DNS server as configured on the computer where Firewall Suite is installed.

Not all IP addresses are resolved. There is a hierarchy to DNS servers. If the first DNS server cannot resolve the IP address, Firewall Suite makes a call to another DNS server to find it. It continues that process until it times out. By default, Firewall Suite gives up on the process after 25 seconds and goes on to the next record.

This article was previously published as:

NETIQKB2648