By ToolzHive · Updated
Assignments are conventions. A reachable port does not prove which application is listening; a timeout can have several causes.
Reference table
| Port | Transport | Typical service |
|---|---|---|
| 20 / 21 | TCP | FTP data / control |
| 22 | TCP | SSH |
| 25 | TCP | SMTP relay |
| 53 | UDP / TCP | DNS |
| 67 / 68 | UDP | DHCP server / client |
| 80 | TCP | HTTP |
| 110 | TCP | POP3 |
| 123 | UDP | NTP |
| 143 | TCP | IMAP |
| 443 | TCP; UDP for HTTP/3 | HTTPS |
| 445 | TCP | SMB |
| 465 | TCP | Submission with implicit TLS |
| 587 | TCP | Message submission |
| 853 | TCP / UDP | DNS over TLS / DTLS |
| 993 | TCP | IMAP with implicit TLS |
| 995 | TCP | POP3 with implicit TLS |
| 3306 | TCP | MySQL |
| 3389 | TCP / UDP | Remote Desktop |
| 5432 | TCP | PostgreSQL |
Match the protocol
A TCP connection probe cannot confirm a UDP service. DNS can use both transports; HTTP/3 uses QUIC over UDP.
Exposure
Restrict database and administration ports to clients that need access. Appearance in a reference is not a reason to expose a service publicly.
Try the related tools
- Open Port Checker — Check whether a TCP port is open and reachable on a public IP address or host.