Linux nslookup Command

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nslookup (Name Server Lookup) is a network management tool used to query Domain Name System (DNS) records. It helps users diagnose and resolve DNS-related issues, and is one of the commonly used command-line tools for Linux system administrators and network engineers.

The main functions of nslookup include:

  • Query the IP address corresponding to a domain name
  • Query the domain name corresponding to an IP address (reverse resolution)
  • Query specific types of DNS records (MX, NS, SOA, etc.)
  • Specify a particular DNS server for queries

Basic Syntax

The basic syntax format of the nslookup command is as follows:

nslookup [选项] [域名/IP] [DNS服务器]

Parameter Description

Parameter Description
Domain/IP The domain name or IP address to query
DNS server Specifies the DNS server to use (optional)

Common Options

Option Description
-type=TYPE Specify the query record type, such as A, MX, NS, etc.
-debug Display debug information
-port=PORT Specify the DNS server port (default 53)
-timeout=SEC Set query timeout time (seconds)
-retry=NUM Set number of retries

Usage Examples

1. Basic Domain Query

Query the A record of a domain name (default):

nslookup example.com

Example output:

Server:         8.8.8.8
Address:        8.8.8.8#53

Non-authoritative answer:
Name:   example.com
Address: 93.184.216.34

2. Query with a Specified DNS Server

Use Google's public DNS server (8.8.8.8) to query:

nslookup example.com 8.8.8.8

3. Query Specific Record Types

Query MX record (mail server):

nslookup -type=MX google.com

Query NS record (name server):

nslookup -type=NS google.com

Query TXT record:

nslookup -type=TXT google.com

4. Reverse DNS Lookup (IP to Domain)

nslookup 8.8.8.8

5. Interactive Mode

Enter interactive mode by typing nslookup without parameters:

Examples

nslookup
> set type=MX
> google.com
> server 8.8.4.4
> example.com
> exit

Common DNS Record Types

Record Type Description Example Command
A IPv4 address record nslookup -type=A example.com
AAAA IPv6 address record nslookup -type=AAAA example.com
MX Mail exchange record nslookup -type=MX example.com
NS Name server record nslookup -type=NS example.com
CNAME Alias record nslookup -type=CNAME www.example.com
TXT Text record nslookup -type=TXT example.com
SOA Start of authority record nslookup -type=SOA example.com

Advanced Usage

1. Debug Mode

nslookup -debug example.com

2. Query DNS Root Servers

nslookup -type=NS .

3. Query a Specific Port

nslookup -port=8053 example.com dns-server.example.com

4. Set Timeout and Retries

nslookup -timeout=10 -retry=3 example.com

Troubleshooting

1. Query Not Responding

Possible causes:

  • Network connection issues
  • DNS server unavailable
  • Firewall blocking DNS queries (port 53)

Solutions:

Examples

# Check network connection
ping 8.8.8.8

# Try other DNS servers
nslookup example.com 8.8.8.8

2. What does "Non-authoritative answer" mean?

It indicates that the returned result comes from a DNS cache, not an authoritative DNS server. To get an authoritative answer, you need to query the domain's authoritative DNS servers.

3. How to query a domain's authoritative DNS servers?

nslookup -type=NS example.com

Alternative Tools

Although nslookup is still widely used, modern Linux systems recommend usingdigorhostcommand:

  1. dig- A more powerful DNS query tool

    dig example.com

  2. host- A simpler DNS query tool

    host example.com

Summary

nslookup is a simple and practical DNS query tool. After reading this article, you should be able to:

  1. Understand the basic usage and common options of nslookup
  2. Query various types of DNS records
  3. Diagnose basic DNS-related problems
  4. Understand the differences between nslookup and other DNS tools

To master nslookup, the best way is to practice more. Try querying websites you frequently visit, or your organization's domain servers, and observe the returned results of different types of DNS records.

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