Security & Networking

DNS Basics

Domain Name System records and configuration.

DNS Record Types

# A Record
example.com to 192.0.2.1 # IPv4

# AAAA Record
example.com to 2001:db8::1 # IPv6

# CNAME Record
www.example.com to example.com # alias

# MX Record
example.com to mail.example.com # mail server
Priority: 10 # lower = higher priority

DNS Lookup Tools

# nslookup
nslookup example.com
nslookup -type=mx example.com

# dig
dig example.com
dig example.com MX
dig example.com +short

# host
host example.com

Flush DNS Cache

# Windows
ipconfig /flushdns

# macOS
sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder

# Linux
sudo systemd-resolve --flush-caches

TTL Values

# Example DNS record
example.com. 3600 IN A 192.0.2.1

# Common TTL values
300 # 5 minutes
3600 # 1 hour
86400 # 24 hours