DNS
Domain Name System
DNS
Domain Name System translates human-readable domain names into IP addresses.
How DNS Works
Resolution Process
1. User enters URL: www.example.com
2. Browser queries recursive resolver (ISP DNS)
3. Resolver queries root nameserver
4. Root returns TLD nameserver address
5. Resolver queries TLD nameserver
6. TLD returns authoritative nameserver
7. Resolver queries authoritative nameserver
8. Authoritative returns IP address
9. Resolver returns IP to browser
10. Browser connects to IP addressDNS Record Types
A Record
Maps domain to IPv4 address
www.example.com A 192.168.1.1AAAA Record
Maps domain to IPv6 address
www.example.com AAAA 2001:db8::1CNAME Record
Canonical name (alias)
blog.example.com CNAME example.comMX Record
Mail exchange (email routing)
example.com MX 10 mail.example.comDNS Tools
# Query DNS
nslookup example.com
dig example.com
host example.com
# Query specific record
dig example.com A
dig example.com MX
# Reverse lookup
dig -x 8.8.8.8
# Trace DNS resolution
dig +trace example.comDNS Ports
Port 53/UDP - DNS queries (default)
Port 53/TCP - Large responses, zone transfersPublic DNS Servers
Google: 8.8.8.8, 8.8.4.4
Cloudflare: 1.1.1.1, 1.0.0.1
Quad9: 9.9.9.9DNS Security
DNSSEC (DNS Security Extensions)
- Cryptographic signing of DNS records
- Prevents DNS spoofing
DNS Filtering
- Block malware domains
- Ad blocking
Best Practices
- Use reliable DNS servers
- Monitor DNS query performance
- Implement DNSSEC
- Cache DNS responses
- Use multiple DNS servers
- Monitor DNS logs
- Keep DNS software updated