dig (Domain Information Groper) DNS Lookup Tool Guide

Table of Contents

• Overview
• Installation
• Basic Syntax
• Query Types
• Advanced Options
• Output Sections
• Troubleshooting
• Best Practices

Overview

dig is a flexible DNS lookup utility that performs DNS lookups and displays the answers from the queried name servers. It’s the preferred tool for DNS troubleshooting by network administrators.

Key Features

• DNS record querying
• DNS server testing
• DNSSEC validation
• Trace DNS resolution path
• Reverse DNS lookups
• Multiple query formats

Installation

Ubuntu (22.04/24.04)

sudo apt update
sudo apt install dnsutils

macOS

# Using Homebrew
brew install bind
 
# Pre-installed on most macOS versions

Basic Syntax

Simple Query

# Basic domain lookup
dig example.com
 
# Short answer
dig example.com +short
 
# Specific record type
dig example.com MX

Query Format

# General format
dig [@server] [domain] [type] [+options]
 
# Example with specific DNS server
dig @8.8.8.8 example.com

Query Types

Common Record Types

# A record (IPv4)
dig example.com A
 
# AAAA record (IPv6)
dig example.com AAAA
 
# MX record (Mail)
dig example.com MX
 
# TXT record
dig example.com TXT
 
# NS record (Nameserver)
dig example.com NS
 
# SOA record (Start of Authority)
dig example.com SOA
 
# CNAME record
dig www.example.com CNAME

Reverse DNS Lookup

# PTR record lookup
dig -x 8.8.8.8
 
# IPv6 reverse lookup
dig -x 2001:db8::1

Advanced Options

Query Options

# Trace DNS resolution path
dig example.com +trace
 
# Use TCP instead of UDP
dig example.com +tcp
 
# Show timing information
dig example.com +stats
 
# Disable recursion
dig example.com +norecurse
 
# DNSSEC validation
dig example.com +dnssec

Multiple Queries

# Multiple record types
dig example.com ANY
 
# Multiple domains
dig example.com google.com
 
# Multiple types for same domain
dig example.com NS MX

Output Control

# Short output
dig example.com +short
 
# Detailed output
dig example.com +noall +answer +authority +additional
 
# Custom output fields
dig example.com +noall +answer +ttl

Output Sections

Understanding dig Output

; <<>> DiG 9.16.1-Ubuntu <<>> example.com
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12345
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
 
;; QUESTION SECTION:
;example.com.			IN	A
 
;; ANSWER SECTION:
example.com.		86400	IN	A	93.184.216.34

Section Explanations

# Show only answer section
dig example.com +noall +answer
 
# Show only authority section
dig example.com +noall +authority
 
# Show only additional section
dig example.com +noall +additional

Troubleshooting

Common Issues

1. DNS Resolution Problems

# Check nameservers
dig example.com NS +short
 
# Verify authoritative servers
dig example.com SOA
 
# Test specific DNS server
dig @8.8.8.8 example.com

2. DNSSEC Validation

# Check DNSSEC
dig example.com +dnssec
 
# Verify DS records
dig example.com DS

3. Response Time Issues

# Show query timing
dig example.com +stats
 
# Compare different servers
dig @8.8.8.8 example.com +stats
dig @1.1.1.1 example.com +stats

Advanced Use Cases

Batch Processing

# Read queries from file
dig -f queries.txt
 
# Output to file
dig example.com > results.txt

DNS Server Testing

# Test response time
dig example.com +tries=1 +retry=0
 
# Check server capabilities
dig chaos txt version.bind @dns.server

AXFR (Zone Transfer)

# Attempt zone transfer
dig @ns1.example.com example.com AXFR
 
# With specific transfer key
dig @ns1.example.com example.com AXFR -k transfer.key

Best Practices

DNS Querying

# Always check authoritative answer
dig example.com +noadditional +noauthority
 
# Verify with multiple DNS servers
dig @8.8.8.8 example.com
dig @1.1.1.1 example.com

Performance Testing

# Measure response time
dig example.com +stats +tries=1
 
# Test multiple queries
for i in {1..5}; do dig example.com +noall +answer; done

Quick Reference

Essential Commands

# Basic lookup
dig example.com
 
# Short answer
dig +short example.com
 
# Specific record
dig example.com MX
 
# Reverse lookup
dig -x IP_ADDRESS
 
# Trace resolution
dig +trace example.com

Common Options

• +short: Brief output
• +trace: Follow delegation chain
• +dnssec: Show DNSSEC info
• +noall: Turn off all display flags
• +answer: Show answer section
• +stats: Show statistics
• +tcp: Use TCP instead of UDP
• +norecurse: Disable recursion

Output Control Options

# Minimal output
dig +noall +answer example.com
 
# Full details
dig +nocmd +noall +answer +authority +additional example.com
 
# Custom timestamp
dig +time=1 +tries=1 example.com

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Remember:

• Always specify record types when needed
• Use +short for scripting
• Check authoritative answers
• Verify DNSSEC when required
• Compare multiple DNS servers
• Document query results

For detailed information, consult the man pages (man dig).