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2.4.1. Common Ports and Protocols
Memorize these—the exam tests port numbers directly:
| Protocol | Port(s) | Transport | Purpose | Secure Alternative |
|---|---|---|---|---|
| FTP | 20 (data), 21 (control) | TCP | File transfer | SFTP (22), FTPS (990) |
| SSH | 22 | TCP | Secure remote access | — |
| Telnet | 23 | TCP | Remote access (insecure) | SSH (22) |
| SMTP | 25 | TCP | Send email | SMTPS (587 submission) |
| DNS | 53 | TCP/UDP | Name resolution | DoH (443), DoT (853) |
| DHCP | 67 (server), 68 (client) | UDP | IP address assignment | — |
| TFTP | 69 | UDP | Simple file transfer | — |
| HTTP | 80 | TCP | Web traffic | HTTPS (443) |
| POP3 | 110 | TCP | Retrieve email (downloads it) | POP3S (995) |
| NTP | 123 | UDP | Time synchronization | NTS |
| IMAP | 143 | TCP | Retrieve email (kept on server) | IMAPS (993) |
| SNMP | 161 (queries), 162 (traps) | UDP | Network management | SNMPv3 |
| LDAP | 389 | TCP | Directory access | LDAPS (636) |
| HTTPS | 443 | TCP | Secure web traffic | — |
| SMB | 445 | TCP | Windows file sharing | — |
| Syslog | 514 | UDP | Log collection | — |
| Microsoft SQL Server | 1433 | TCP | Database access | — |
| RDP | 3389 | TCP | Remote desktop | — |
| SIP | 5060 (plain), 5061 (TLS) | TCP/UDP | VoIP signaling | 5061 |
⚠️ Exam Trap: Know which ports use TCP vs. UDP. DNS uses both—UDP for standard queries (fast), TCP for zone transfers and large responses (reliable). DHCP and TFTP are UDP-only. Web protocols (HTTP, HTTPS, SMTP) use TCP for reliability.
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Written byAlvin Varughese
Founder•20 professional certifications