Ports & Protocols

A port (0–65535) lets one host run many services. Memorize: 21 FTP (cleartext), 22 SSH, 23 Telnet (cleartext), 53 DNS, 80 HTTP, 443 HTTPS, 445 SMB, 3306 MySQL, 3389 RDP.

The recurring lesson: encryption is a choice, and its absence is a finding. A banner like 220 (vsFTPd 3.0.3) hands an attacker software and version.