nslookup

Overview

The nslookup command queries Internet name servers for DNS (Domain Name System) information. It’s used for diagnosing DNS problems and verifying DNS records.

Syntax

nslookup [options] [hostname|IP] [server]

Common Options

Option Description
-type=a Address record
-type=aaaa IPv6 address
-type=mx Mail server
-type=ns Name server
-type=soa Start of authority
-type=txt Text record
-type=ptr Pointer record
-type=cname Canonical name
-debug Debug mode
-port=N Server port
-timeout=N Query timeout
-query=type Set query type

Key Use Cases

  1. DNS troubleshooting
  2. Record verification
  3. Mail server lookup
  4. Reverse DNS
  5. Domain validation

Examples with Explanations

Example 1: Basic Lookup

nslookup google.com

Look up IP address

Example 2: Mail Servers

nslookup -type=mx domain.com

Find mail servers

Example 3: Name Servers

nslookup -type=ns domain.com

Find name servers

Understanding Output

Example output:

Server:   192.168.1.1
Address:  192.168.1.1#53

Name:     google.com
Address:  172.217.167.78

Components: - DNS server used - Query result - Record details

Common Usage Patterns

  1. Address lookup:

    nslookup hostname

  2. Reverse lookup:

    nslookup IP_address

  3. Specific server:

    nslookup domain.com 8.8.8.8

Performance Analysis

  • Response time
  • Record availability
  • Server reliability
  • Cache effects
  • Resolution chain

Additional Resources

Best Practices

  1. Verify multiple servers
  2. Check all record types
  3. Document results
  4. Regular testing
  5. Compare responses

Troubleshooting

  1. Resolution failures
  2. Timeout issues
  3. Server problems
  4. Cache issues
  5. Record conflicts

Record Types

  1. A (Address)
  2. AAAA (IPv6)
  3. MX (Mail)
  4. NS (Nameserver)
  5. CNAME (Alias)