Nslookup (short for name server lookup ) is a network utility program used to get information about internet servers. As its name suggests, it finds the nameserver’s information for the domains by querying the domain name system (DNS).
Most computer operating systems include a built-in command-line program in the same name. Some network providers also host web-based services of this same utility (like Network-Tools.com).
These programs are all designed to perform a name server lookup against a specified domain name.
How to use nslookup in Windows
To use the Windows version of nslookup, open a Command Prompt and type nslookup to get results similar to this but with entries for the DNS server and the IP address your computer is using:
C: > nslookup
This command determines which DNS server the computer is currently configured to use for its DNS lookup. As the example shows, this machine is using an OpenDNS DNS server.
Take note of the> small at the bottom of the output of the command. nslookup still runs in the background after the command is issued. The prompt at the end of the output allows you to enter additional parameters.
Either type the domain for which you want nslookup details or exit nslookup with the exit command (or the Ctrl + C keyboard shortcut) to go another way.
You can use nslookup instead by typing the command before the domain name, all on the same line, like nslookup lifewire.com.
Here is an output example:
> nslookup lifewire.com
Look up the username
In DNS, so-called “unauthorized responses” refer to DNS records stored on third-party DNS servers that they obtain from sourcing “proprietary” servers.
Here’s how to get that information (assuming you entered nslookup into the Command Prompt):
> set type = ns
dns1.p08.nsone.net internet address = 184.108.40.206
dns2.p08.nsone.net internet address = 220.127.116.11
dns3.p08.nsone.net internet address = 18.104.22.168
dns4.p08.nsone.net internet address = 22.214.171.124
ns1.p30.dynect.net internet address = 126.96.36.199
ns2.p30.dynect.net internet address = 188.8.131.52
ns3.p30.dynect.net internet address = 184.108.40.206
ns4.p30.dynect.net internet address = 220.127.116.11
An authoritative address lookup can be performed by identifying one of the domain name registrars. nslookup then uses that server instead of the local system’s default DNS server information.
C: > nslookup lifewire.com ns1.p30.dynect.net
The output no longer mentions the “unauthorized” data because the nameserver ns1.p30.dynect is the primary name server for Lifewire.com, as listed in the “NS Records” section of the entries enter its DNS.
Mail Server Lookup
To find mail server information on a specific domain, nslookup uses the DNS MX record feature. Some websites, like Lifewire.com, support both server and server redundancy.
Mail server queries for Lifewire.com jobs are as follows:
> set type = mx
lifewire.com MX preference = 20, mail exchanger = ALT1.ASPMX.L.GOOGLE.com
lifewire.com MX preference = 10, mail exchanger = ASPMX.L.GOOGLE.com
lifewire.com MX preference = 50, mail exchanger = ALT4.ASPMX.L.GOOGLE.com
lifewire.com MX preference = 40, mail exchanger = ALT3.ASPMX.L.GOOGLE.com
lifewire.com MX preference = 30, mail exchanger = ALT2.ASPMX.L.GOOGLE.com
Other nslookup queries
nslookup supports querying other less commonly used DNS records, including CNAME, PTR, and SOA. Type a question mark (?) At the prompt to print the program’s help instructions.
Several web-based variations of the add-on provide some extra features beyond the standard specifications found in Windows tools.
How to Use Online nslookup Tools
The nslookup online utilities, like the one from Network-Tools.com, allow you to customize further what’s allowed with the command from Windows.
For example, after selecting a domain, server, and port, you can choose from the drop-down list of query types. Examples include an address, hostname, canonical name, start authority, mailbox domain name, mail group member, well-known services, mail exchange, ISDN addresses, NSAP addresses, and many more.
You can also choose the query class; internet, CHAOS, or Hesiod.