Common Ports

Port ranges

• 0–1023 — well-known ports. Standard services (HTTP, SSH, DNS); binding to them needs root/admin privileges on Unix systems.
• 1024–49151 — registered ports. Databases, message queues and applications register here (MySQL 3306, PostgreSQL 5432).
• 49152–65535 — ephemeral ports. Assigned temporarily to the client side of outgoing connections.

Frequently asked questions

TCP or UDP — what's the difference?

TCP guarantees delivery and order (web, mail, databases); UDP just sends and hopes (DNS lookups, video calls, game traffic) — losing a packet beats waiting for it. Some services use both: DNS queries ride UDP 53 but switch to TCP 53 for large responses.

Why won't my app start — "port already in use"?

Something else is bound to it. Find the culprit with lsof -i :3000 (macOS/Linux) or netstat -ano | findstr :3000 (Windows), then stop it or run your app on another port.

Is it safe to expose these ports to the internet?

Only what must be public — usually 80/443. Databases, Redis and RDP on public IPs are the most-scanned targets on the internet; put them behind a VPN or firewall and you disappear from those scans.