Port 53 (UDP & TCP) — Domain Name System (DNS)
DNS translates human-readable domain names into IPv4 (A) and IPv6 (AAAA) addresses, and publishes email authentication TXT, MX, SRV, and CAA records.
| Port Number | 53 |
|---|---|
| Transport Protocol | UDP & TCP |
| Primary Service | Domain Name System (DNS) |
| Standard / Specification | RFC 1035 / RFC 7766 |
| IANA Port Range | Well-Known System Port (0–1023) |
| Internet Exposure Risk | Open recursive resolvers are prime targets for DNS amplification DDoS attacks. |
Firewall Architecture & Hardening Best Practices
Firewall rules for authoritative or recursive DNS servers MUST permit BOTH UDP/53 (standard fast queries) and TCP/53 (responses exceeding EDNS0 limits, DNSSEC payloads, and AXFR/IXFR zone transfers).
Operational Troubleshooting Note
Test UDP vs TCP DNS path behavior directly with dig @1.1.1.1 example.com and dig +tcp @1.1.1.1 example.com.
Quick CLI Connectivity & Firewall Reference
# Test TCP/53 reachability (Linux / macOS / PowerShell) nc -zv target.example.com 53 Test-NetConnection -ComputerName target.example.com -Port 53 # Inspect local UDP/53 socket binding on Linux ss -uapn | grep :53 # Allow restricted CIDR on Linux UFW firewall ufw allow from 10.0.0.0/8 to any port 53 proto any
Planning firewall allowlists or VPN overlays? Use our IPv4 CIDR Calculator, MTU & TCP MSS Calculator, or WireGuard AllowedIPs Generator.
Browse Common Network & Cloud Ports
Port 22 (SSH) Port 25 (SMTP Mail Relay) Port 53 (Domain Name System) Port 67 (DHCPv4 Server) Port 80 (HTTP Web Traffic) Port 123 (Network Time Protocol) Port 161 (SNMP Polling) Port 179 (Border Gateway Protocol) Port 389 (LDAP Directory) Port 443 (HTTPS & HTTP) Port 445 (SMB Direct File Sharing) Port 465 (SMTPS Implicit TLS Submission) Port 500 (IPsec IKEv2 Key Exchange) Port 514 (Syslog Telemetry) Port 587 (SMTP Mail Submission) Port 636 (LDAPS) Port 853 (DNS over TLS) Port 993 (IMAPS Encrypted Mailbox) Port 1194 (OpenVPN Tunnel) Port 1433 (Microsoft SQL Server) Port 1812 (RADIUS Authentication) Port 2049 (Network File System) Port 2379 (etcd Client API) Port 3306 (MySQL & MariaDB) Port 3389 (Remote Desktop Protocol) Port 4500 (IPsec NAT Traversal) Port 5432 (PostgreSQL Database) Port 6379 (Redis) Port 6443 (Kubernetes API Server) Port 51820 (WireGuard VPN)