Common Ports and Protocols Reference
One-page companion for Module 5. A port is the number that steers arriving data to the right program — know this table and half of every firewall rule reads itself.
The three IANA ranges
| Range | Name | Who uses it |
|---|---|---|
| 0–1023 | System (well-known) | Standard services: web, mail, DNS... |
| 1024–49151 | Registered | Vendor applications (e.g. 3389 RDP) |
| 49152–65535 | Dynamic (ephemeral) | Your OS, as the temporary client side |
Servers listen on fixed low ports; your machine replies from a random dynamic port — the pair of them identifies the conversation.
The beginner's core table
| Port | Protocol | Transport | 2026 status |
|---|---|---|---|
| 20/21 | FTP (file transfer) | TCP | Legacy — plaintext; use SFTP over 22 |
| 22 | SSH / SFTP | TCP | Current |
| 23 | Telnet | TCP | Legacy — plaintext; replaced by SSH |
| 25 | SMTP (server↔server relay) | TCP | Current for relay only — not your mail app |
| 53 | DNS | TCP + UDP | Current |
| 67/68 | DHCP (server/client) | UDP | Current |
| 80 | HTTP | TCP | Current — usually just redirects to 443 |
| 110 | POP3 | TCP | Legacy — plaintext; use 995 |
| 123 | NTP (time sync) | UDP | Current |
| 143 | IMAP | TCP | Legacy — plaintext; use 993 |
| 161 | SNMP (monitoring) | UDP | Current |
| 443 | HTTPS | TCP (+ UDP — see QUIC) | Current — the universal door |
| 465/587 | Mail submission over TLS | TCP | Current — how your mail app sends |
| 853 | DNS over TLS (DoT) | TCP | Current |
| 993 | IMAPS (secure IMAP) | TCP | Current |
| 995 | POP3S (secure POP3) | TCP | Current |
| 3389 | RDP (remote desktop) | TCP | Current — never expose it to the Internet |
QUIC note. HTTP/3 rides QUIC on UDP 443: TCP-style reliability plus TLS, rebuilt over UDP. About one-fifth of web requests travel this way (2025–26), so "443 = TCP" is no longer the whole story.
Ports in commands
- Linux:
ss -tlnp— listening TCP ports and the programs behind them. - Windows:
netstat -ab(administrator prompt) — same idea. - PowerShell reachability test:
Test-NetConnection example.com -Port 443.
Network Essentials · Module 5 · Turning Point Academy — backbone: Al-Doori, Network Essentials, Ch. 5 & 6.