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Dig - DNS Lookup and Troubleshooting ​

Dig (Domain Information Groper) is a powerful command-line tool for DNS lookup and troubleshooting. It's more flexible and provides more detailed output than nslookup, making it the preferred tool for DNS diagnostics and investigation.

Basic Usage ​

Simple DNS Lookup ​

bash
# Basic A record lookup
dig google.com
dig example.com
dig github.com

# Lookup with specific DNS server
dig @8.8.8.8 google.com
dig @1.1.1.1 google.com
dig @208.67.222.222 google.com

# Short output (just the answer)
dig +short google.com
dig +short @8.8.8.8 google.com

Specifying Record Types ​

bash
# A record (IPv4 address)
dig google.com A
dig +short google.com A

# AAAA record (IPv6 address)
dig google.com AAAA
dig +short google.com AAAA

# MX record (mail exchange)
dig google.com MX
dig +short google.com MX

# NS record (name servers)
dig google.com NS
dig +short google.com NS

# TXT record (text records)
dig google.com TXT
dig +short google.com TXT

# CNAME record (canonical name)
dig www.google.com CNAME
dig +short www.google.com CNAME

# SOA record (start of authority)
dig google.com SOA
dig +short google.com SOA

# PTR record (reverse DNS)
dig google.com PTR

# ANY record (all available records)
dig google.com ANY

DNS Server Specification ​

Using Different DNS Servers ​

bash
# Google DNS
dig @8.8.8.8 google.com
dig @8.8.4.4 google.com

# Cloudflare DNS
dig @1.1.1.1 google.com
dig @1.0.0.1 google.com

# OpenDNS
dig @208.67.222.222 google.com
dig @208.67.220.220 google.com

# Quad9 DNS
dig @9.9.9.9 google.com
dig @149.112.112.112 google.com

# Local DNS server
dig @192.168.1.1 google.com

# Multiple servers (dig will try each)
dig @8.8.8.8 @1.1.1.1 google.com

IPv6 DNS Servers ​

bash
# Google IPv6 DNS
dig @2001:4860:4860::8888 google.com
dig @2001:4860:4860::8844 google.com

# Cloudflare IPv6 DNS
dig @2606:4700:4700::1111 google.com
dig @2606:4700:4700::1001 google.com

# OpenDNS IPv6
dig @2620:119:35::35 google.com
dig @2620:119:53::53 google.com

Output Control Options ​

Formatting Output ​

bash
# Short output (answer only)
dig +short google.com

# Show only answer section
dig +noall +answer google.com

# Show only authority section
dig +noall +authority google.com

# Show only additional section
dig +noall +additional google.com

# Show question and answer
dig +noall +question +answer google.com

# Multiline output
dig +multiline google.com

# No comments
dig +nocomments google.com

# No statistics
dig +nostats google.com

# No question section
dig +noquestion google.com

# No answer section
dig +noanswer google.com

# No authority section
dig +noauthority google.com

# No additional section
dig +noadditional google.com

Detailed Tracing ​

bash
# Trace the full DNS resolution path
dig +trace google.com

# Trace with short output
dig +trace +short google.com

# Trace specific record type
dig +trace google.com MX

# Show all name servers for domain
dig +nssearch google.com

# Show all name servers with details
dig +nssearch +noall +answer google.com

Advanced Query Options ​

Query Behavior ​

bash
# Disable recursion
dig +norecurse google.com

# Use TCP instead of UDP
dig +tcp google.com
dig +vc google.com

# Force UDP (default)
dig +notcp google.com

# Set query timeout
dig +time=5 google.com
dig +time=10 google.com

# Set number of tries
dig +tries=3 google.com

# Set number of retries
dig +retry=2 google.com

# Set UDP buffer size
dig +bufsize=512 google.com
dig +bufsize=4096 google.com

# Enable EDNS
dig +edns=0 google.com

# Ignore truncation
dig +ignore google.com

# Fail on truncation
dig +fail google.com

DNSSEC Options ​

bash
# Request DNSSEC records
dig +dnssec google.com

# Check DNSSEC validation
dig +cd google.com

# Request authentic data
dig +ad google.com

# Show DNSSEC chain
dig +trace +dnssec google.com

# Validate DNSSEC signatures
dig +sigchase google.com

# Show DNSKEY records
dig google.com DNSKEY

# Show DS records
dig google.com DS

# Show RRSIG records
dig google.com RRSIG

Reverse DNS Lookups ​

PTR Record Queries ​

bash
# Reverse lookup using -x flag
dig -x 8.8.8.8
dig -x 1.1.1.1
dig -x 192.168.1.1

# Manual PTR lookup
dig 8.8.8.8.in-addr.arpa PTR
dig 1.1.1.1.in-addr.arpa PTR

# IPv6 reverse lookup
dig -x 2001:4860:4860::8888

# Short reverse lookup
dig +short -x 8.8.8.8

# Reverse lookup with specific server
dig @8.8.8.8 -x 1.1.1.1

Batch Queries ​

Multiple Domains ​

bash
# Query multiple domains
dig google.com yahoo.com microsoft.com

# Query from file
echo -e "google.com\nyahoo.com\nmicrosoft.com" > domains.txt
dig -f domains.txt

# Query different record types for same domain
dig google.com A MX NS TXT

# Batch with specific server
dig @8.8.8.8 -f domains.txt

Scripted Queries ​

bash
# Loop through domains
for domain in google.com yahoo.com microsoft.com; do
    echo "=== $domain ==="
    dig +short $domain
done

# Check multiple record types
for type in A AAAA MX NS TXT; do
    echo "=== $type records for google.com ==="
    dig +short google.com $type
done

Specialized DNS Records ​

bash
# MX records (mail exchange)
dig google.com MX
dig +short google.com MX

# SPF records (in TXT)
dig google.com TXT | grep "v=spf1"
dig _spf.google.com TXT

# DMARC records
dig _dmarc.google.com TXT

# DKIM records
dig selector1._domainkey.google.com TXT

# Mail server A records
dig gmail-smtp-in.l.google.com A

Service Discovery Records ​

bash
# SRV records (service records)
dig _sip._tcp.example.com SRV
dig _xmpp-server._tcp.example.com SRV
dig _minecraft._tcp.example.com SRV

# CAA records (certificate authority authorization)
dig google.com CAA

# NAPTR records (naming authority pointer)
dig example.com NAPTR

# LOC records (location)
dig example.com LOC

Security Records ​

bash
# TLSA records (DNS-based authentication)
dig _443._tcp.example.com TLSA
dig _25._tcp.mail.example.com TLSA

# SSHFP records (SSH fingerprints)
dig example.com SSHFP

# CERT records (certificates)
dig example.com CERT

Troubleshooting DNS Issues ​

Common Diagnostics ​

bash
# Check if domain exists
dig +short google.com

# Check authoritative name servers
dig +short google.com NS

# Query authoritative server directly
dig @ns1.google.com google.com

# Check SOA record for domain info
dig google.com SOA

# Trace full resolution path
dig +trace google.com

# Check for DNS propagation
dig @8.8.8.8 example.com
dig @1.1.1.1 example.com
dig @208.67.222.222 example.com

Error Diagnosis ​

bash
# Check for NXDOMAIN (domain doesn't exist)
dig nonexistent.google.com

# Check for SERVFAIL
dig +trace problematic.domain.com

# Check for timeout issues
dig +time=1 +tries=1 slow.server.com

# Check for truncation
dig +bufsize=512 large.response.com

# Verify DNSSEC
dig +dnssec +cd google.com

Network Path Analysis ​

bash
# Test different DNS servers
for server in 8.8.8.8 1.1.1.1 208.67.222.222; do
    echo "Testing $server:"
    dig @$server +time=3 google.com | grep "Query time"
done

# Check local vs remote DNS
dig @127.0.0.1 google.com
dig @8.8.8.8 google.com

# Test UDP vs TCP
dig +notcp google.com
dig +tcp google.com

Performance Testing ​

Query Timing ​

bash
# Show query time
dig google.com | grep "Query time"

# Multiple queries for average
for i in {1..5}; do
    dig google.com | grep "Query time"
done

# Time multiple servers
for server in 8.8.8.8 1.1.1.1 208.67.222.222; do
    echo "Server: $server"
    dig @$server google.com | grep "Query time"
done

Load Testing ​

bash
# Rapid queries (be careful with rate limiting)
for i in {1..10}; do
    dig +short google.com &
done
wait

# Measure DNS cache performance
dig google.com  # First query (cache miss)
dig google.com  # Second query (cache hit)

Configuration and Customization ​

Using .digrc Configuration ​

bash
# Create ~/.digrc for default options
echo "+short" > ~/.digrc
echo "+time=5" >> ~/.digrc
echo "+tries=2" >> ~/.digrc

# Override config file
dig +noconfig google.com

Environment Variables ​

bash
# Set default options
export DIG_OPTIONS="+short +time=5"
dig google.com

# Set default server
export DIG_SERVER="8.8.8.8"
dig google.com

Integration with Other Tools ​

Combining with Other Commands ​

bash
# Extract IP addresses
dig +short google.com | grep -E '^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$'

# Get all A records and ping them
dig +short google.com A | while read ip; do
    echo "Pinging $ip"
    ping -c 1 $ip
done

# Check if domain resolves to specific IP
if dig +short google.com | grep -q "172.217."; then
    echo "Domain resolves to Google IP range"
fi

# Compare DNS responses
diff <(dig @8.8.8.8 +short google.com) <(dig @1.1.1.1 +short google.com)

Scripting Examples ​

bash
#!/bin/bash
# DNS health check script

DOMAIN="example.com"
SERVERS=("8.8.8.8" "1.1.1.1" "208.67.222.222")

echo "DNS Health Check for $DOMAIN"
echo "================================"

for server in "${SERVERS[@]}"; do
    echo "Testing server: $server"
    
    # Test A record
    A_RECORD=$(dig @$server +short $DOMAIN A)
    if [ -n "$A_RECORD" ]; then
        echo "  A Record: $A_RECORD"
    else
        echo "  A Record: FAILED"
    fi
    
    # Test query time
    QUERY_TIME=$(dig @$server $DOMAIN | grep "Query time" | awk '{print $4}')
    echo "  Query Time: ${QUERY_TIME}ms"
    
    echo ""
done

Cross-Platform Considerations ​

Linux ​

bash
# Install dig (usually part of bind-utils or dnsutils)
sudo apt install dnsutils          # Ubuntu/Debian
sudo yum install bind-utils         # RHEL/CentOS
sudo dnf install bind-utils         # Fedora

# Alternative tools
host google.com                     # Simple DNS lookup
nslookup google.com                 # Interactive DNS lookup

macOS ​

bash
# dig is pre-installed on macOS
dig google.com

# Install via Homebrew for latest version
brew install bind

# Alternative tools
host google.com
nslookup google.com

Windows ​

cmd
# dig is not included by default
# Download from ISC BIND or use alternatives

# Windows alternatives
nslookup google.com
Resolve-DnsName google.com          # PowerShell

Best Practices ​

Security Considerations ​

  • Use trusted DNS servers for sensitive queries
  • Be aware that DNS queries can be logged
  • Consider using DNS over HTTPS (DoH) or DNS over TLS (DoT)
  • Validate DNSSEC when security is critical

Performance Tips ​

  • Use +short for scripting to reduce output parsing
  • Set appropriate timeouts for your network
  • Use local DNS caching when possible
  • Consider the impact of DNS queries on rate limiting

Troubleshooting Methodology ​

  1. Start with basic queries to verify connectivity
  2. Use +trace to understand the resolution path
  3. Test multiple DNS servers to isolate issues
  4. Check both forward and reverse DNS
  5. Verify DNSSEC when applicable

Monitoring and Automation ​

  • Log DNS query times for performance monitoring
  • Set up alerts for DNS resolution failures
  • Use batch queries for efficiency
  • Implement proper error handling in scripts

Dig is an essential tool for DNS troubleshooting and investigation. Its flexibility and detailed output make it invaluable for network administrators, security professionals, and developers working with DNS-dependent applications.