Whitepaper discussing various port scanning techniques with explanations, diagrams, and examples using Nmap and Hping3. PDF version.
You can download it from the following link: https://packetstormsecurity.com/files/download/54974/port-scanning-techniques.pdf
Source: https://packetstormsecurity.com/files/54974/Port-Scanning-Techniques-Whitepaper.html