About nslookup

In this post, we will explore nslookup (Name Server Lookup) and its practical usage examples.

What is nslookup?

nslookup is a command-line tool that allows you to query DNS (Domain Name System) records. With it, you can:

Obtain the IP address of a given hostname or domain.
Perform reverse DNS lookups (find the hostname associated with an IP address).

Installation

If the nslookup command is not found on your CentOS machine, you need to install the bind-utils package. Here’s how:

Error Example:

$ nslookup google.com
-bash: nslookup: command not found

Installation:

Run the following command:

$ yum install bind-utils

Once installed, you can start using the nslookup command.

nslookup Command Examples

Here are some commonly used nslookup commands:

1. Display the IP Address of a Domain

Use the nslookup command followed by a domain name to retrieve its IP address.

$ nslookup justgeek.in
Server:         8.8.8.8
Address:        8.8.8.8#53

Non-authoritative answer:
Name:   justgeek.in
Address: 151.101.2.159

2. Fetch DNS Records

Retrieve specific DNS records, such as MX (Mail Exchange) records, using the -type option.

Example: Retrieve MX Records

$ nslookup -type=mx justgeek.in
Server:         8.8.8.8
Address:        8.8.8.8#53

Non-authoritative answer:
justgeek.in     mail exchanger = 30 mx3.zoho.in.
justgeek.in     mail exchanger = 20 mx2.zoho.in.
justgeek.in     mail exchanger = 10 mx.zoho.in.

3. Find Name Servers

To list the nameservers of a domain, use the nslookup command without any additional flags.

$ nslookup -type=ns justgeek.in
Server:         8.8.8.8
Address:        8.8.8.8#53

Non-authoritative answer:
justgeek.in     nameserver = jerome.ns.cloudflare.com.
justgeek.in     nameserver = kia.ns.cloudflare.com.

4. Perform Reverse DNS Lookup

Use an IP address as input to find the associated hostname.

$ nslookup 45.77.77.200
200.77.77.45.in-addr.arpa       name = 45.77.77.200.vultrusercontent.com.

5. Query a Specific DNS Server

Specify a particular DNS server to query by appending its address to the nslookup command.

$ nslookup redhat.com ns1.redhat.com
Server:         ns1.redhat.com
Address:        209.132.186.218#53

Non-authoritative answer:
Name:   redhat.com
Address: 209.132.183.105

Conclusion

The nslookup command is a powerful tool for querying and troubleshooting DNS records. Itâs especially useful for network administrators and developers who work with DNS configurations.