The port numbers worth knowing — web, mail, remote access, databases and dev servers.
| Port | Service | Proto | Used for |
|---|---|---|---|
| 80 | HTTP | TCP | Unencrypted web |
| 443 | HTTPS | TCP | Encrypted web (TLS) |
| 8080 | HTTP-alt | TCP | Proxies and dev web |
| 25 | SMTP | TCP | Mail relay between servers |
| 587 | SMTP | TCP | Mail submission (STARTTLS) |
| 465 | SMTPS | TCP | Mail submission (SSL) |
| 143 | IMAP | TCP | Mail retrieval |
| 993 | IMAPS | TCP | IMAP over SSL |
| 110 | POP3 | TCP | Mail retrieval (older) |
| 995 | POP3S | TCP | POP3 over SSL |
| Port | Service | Proto | Used for |
|---|---|---|---|
| 22 | SSH | TCP | Secure shell and SFTP |
| 21 | FTP | TCP | File transfer (control) |
| 23 | Telnet | TCP | Unencrypted remote shell |
| 3389 | RDP | TCP | Windows Remote Desktop |
| 5900 | VNC | TCP | Remote desktop |
| Port | Service | Proto | Used for |
|---|---|---|---|
| 53 | DNS | UDP/TCP | Domain name lookups |
| 123 | NTP | UDP | Time synchronisation |
| 67 | DHCP | UDP | IP assignment (server) |
| 389 | LDAP | TCP | Directory services |
| 636 | LDAPS | TCP | LDAP over SSL |
| Port | Service | Proto | Used for |
|---|---|---|---|
| 3306 | MySQL | TCP | MySQL / MariaDB |
| 5432 | PostgreSQL | TCP | Postgres |
| 6379 | Redis | TCP | Redis cache / store |
| 27017 | MongoDB | TCP | MongoDB |
| 1433 | MS SQL | TCP | SQL Server |
| 11211 | Memcached | TCP | Memcached |
| Port | Service | Proto | Used for |
|---|---|---|---|
| 3000 | Dev server | TCP | Node / React dev |
| 5173 | Vite | TCP | Vite dev server |
| 8000 | Dev server | TCP | Django / Python dev |
| 5000 | Dev server | TCP | Flask / .NET dev |
A port number tells the operating system which program a network connection belongs to: an IP address gets you to the machine, and the port gets you to the right service on it. Ports 0–1023 are the well-known ports reserved for standard services (HTTP on 80, HTTPS on 443, SSH on 22), 1024–49151 are registered ports for specific applications, and the rest are ephemeral ports the OS hands out to outgoing connections. The two you'll touch most are 443 for HTTPS and 22 for SSH; the database and dev-server ports above are the ones that come up when something local won't connect. A blocked or wrong port is a common cause of "connection refused", so it's worth confirming the service is actually listening where you expect. For working over SSH, see the SSH commands.