NMAP is a free and open-source utility for network discovery and security auditing. It uses raw IP packets to discern what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and many other characteristics.
The -F option in NMAP stands for “Fast”. When you use the “-F” option, NMAP performs a faster scanning. It accomplishes this speed by reducing the number of ports being scanned. Instead of scanning over 1000 ports, it scans only the most common 100 ports. This option can be quite useful when you are short on time or just want a quick overview of most common open ports in the system you are examining.
For example, normally when you run a NMAP scan without any options, it scans over 1000 ports. The command line might look something like this:
nmap [IP address]
As a result of this scan, you’ll get a detailed report of open, closed, and filtered ports within the range of 1-1024.
When you use the -F option, the command line will look like this:
nmap -F [IP address]
And the resulting report will be much shorter and faster to generate, showing only the 100 most commonly used ports.
While using -F option can speed up the scanning process, remember that it can also cause you to overlook some ports that may be of interest. If you need to conduct a thorough security audit, you might want to do a full port scan instead to make sure you’re not missing anything.
Though it can’t replace a comprehensive scan, the -F option is a valuable tool to have in the toolbox for system administrators and security analysts alike. It’s all about finding the right balance between time and thoroughness.
Sources used:
1. “Nmap – Network Mapper.” nmap.org, https://nmap.org/book/man.html. Accessed 29 Jan 2023.
2. “Nmap for Beginners – The Basics.” cybrary.it, https://www.cybrary.it/blog/nmap-for-beginners-the-basics/. Accessed 29 Jan 2023.
3. “Network Scanning: Chapter 10 – Faster Scanning.” Nmap Network Scanning, https://nmap.org/book/man-performance.html. Accessed 29 Jan 2023.
