nslookup - Linux

Overview

nslookup is a network administration command-line tool available on Unix-like operating systems. It is used for querying the Domain Name System (DNS) to obtain domain name or IP address mapping or any specific DNS record. It is particularly useful in diagnosing DNS problems but is considered deprecated in favor of newer tools like dig.

Syntax

The basic syntax of the nslookup command is:

nslookup [option] [hostname|IP_address] [server]
  • hostname|IP_address: the domain name or IP address you want to query.
  • server: the DNS server you want to use for the query.

Options/Flags

nslookup has several options that can alter its behavior:

  • -version: Displays the version of the nslookup.
  • -query=type or -type=type: Specifies the type of the query (e.g., A, MX, TXT).
  • -port=number: Specifies the DNS server port number.
  • -timeout=seconds: Sets the timeout interval for a response.
  • -retry=number: Sets the number of retries for the command.
  • -debug: Turns on debug mode, which provides detailed information about the query.

Examples

1. Basic DNS query:

nslookup example.com

This command queries the DNS for the IP address associated with example.com.

2. Querying a specific DNS type record:

nslookup -query=MX google.com

This queries the Mail Exchange (MX) records for google.com.

3. Using a specific DNS server:

nslookup example.com 8.8.8.8

This sends the query to the DNS server at IP 8.8.8.8 (Google DNS) instead of the default system DNS server.

Common Issues

  • Timeouts or No Response: This can be due to network issues, incorrect DNS server, or the queried host not existing. Check network connectivity, verify the DNS server address, or ensure the hostname is correct.
  • Non-authoritative answer: This means the answer comes from the server’s cache rather than the authoritative DNS server. Use more specific DNS queries or try a different DNS server.

Integration

nslookup can be combined with other command-line tools for scripting or complex querying:

Example of using nslookup in a script to check DNS records for multiple domains listed in a file:

while read domain; do
  nslookup $domain >> dns_records.txt
done < domains.txt
  • dig: Offers more detailed queries than nslookup and is generally preferred for debugging and analyzing DNS issues.
  • host: Another simple utility for performing DNS lookups.

For additional resources or official documentation, the following links can be helpful:

This manual provides a foundation for using nslookup effectively in various network management and troubleshooting scenarios.