Common Ports & Protocols
The well-known ports you must recognize for CompTIA Network+, Security+, and A+. Insecure protocols are paired with their encrypted replacements, a favorite exam theme.
Well-known ports
| Port | Protocol | Transport | Purpose |
|---|---|---|---|
| 20 / 21 | FTP | TCP | File transfer (data / control), cleartext |
| 22 | SSH / SFTP / SCP | TCP | Secure shell and secure file transfer |
| 23 | Telnet | TCP | Remote CLI, cleartext, insecure |
| 25 | SMTP | TCP | Email routing between servers |
| 53 | DNS | TCP/UDP | Name resolution |
| 67 / 68 | DHCP | UDP | Dynamic address assignment |
| 69 | TFTP | UDP | Trivial file transfer (no auth) |
| 80 | HTTP | TCP | Web, cleartext |
| 110 | POP3 | TCP | Email retrieval (download) |
| 123 | NTP | UDP | Time synchronization |
| 143 | IMAP | TCP | Email retrieval (sync) |
| 161 / 162 | SNMP | UDP | Device monitoring / traps |
| 389 | LDAP | TCP/UDP | Directory services, cleartext |
| 443 | HTTPS | TCP | Web over TLS |
| 445 | SMB | TCP | Windows file sharing |
| 636 | LDAPS | TCP | Directory services over TLS |
| 993 | IMAPS | TCP | IMAP over TLS |
| 995 | POP3S | TCP | POP3 over TLS |
| 3389 | RDP | TCP | Remote Desktop |
| 3306 | MySQL | TCP | Database |
| 1433 | MS SQL | TCP | Database |
Insecure → secure protocol pairs
| Insecure | Port | Secure replacement | Port |
|---|---|---|---|
| Telnet | 23 | SSH | 22 |
| FTP | 21 | SFTP / FTPS | 22 / 990 |
| HTTP | 80 | HTTPS | 443 |
| LDAP | 389 | LDAPS | 636 |
| SNMPv1/v2c | 161 | SNMPv3 | 161 |
| POP3 / IMAP | 110 / 143 | POP3S / IMAPS | 995 / 993 |
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