Introduction: The Scout
You have an IP address, but you don't know what it does. Is it a web server? A camera? A vulnerable database? To find out, hackers and security professionals alike use Nmap (Network Mapper). It is the premier open-source utility for network discovery.
The SYN Scan
By typing nmap -sS 192.168.1.1, you initiate a 'Stealth SYN Scan'. Nmap rapidly knocks on every one of the 65,535 possible ports on that IP address. By listening precisely to how the server responds to the knock, Nmap creates a list of every open door and can even guess the exact Operating System running on the server.
Conclusion
Nmap is the first step in any penetration test. It turns a blank IP address into a detailed map of vulnerabilities. Scan your external ports here.