NMAP is a highly powerful and versatile open-source tool used for network exploration and security auditing. At times, NMAP scanning can be a slow process, which demands patience. However, your NMAP analysis speed can be enhanced in several ways.
1. Choose a faster scanning method: According to NMAP documentation, some scanning techniques are faster than others. In particular, the TCP SYN scan (nmap -sS) and the UDP scan (nmap -sU) are typically much quicker than, for instance, the TCP connect scan (nmap -sT) (NMAP.org, 2021).
1. Increase the timing value: The ‘-T’ option in NMAP allows you to change the timing template, on a scale of 0-5. The higher the number, the faster (and less detailed) the scan. By setting the timing to aggressive (nmap -T4) or insane (nmap -T5), you can speed up your NMAP scanning process. The trade-off is a reduction in accuracy and the possibility of skipped targets due to networking restrictions (StationX, 2018).
1. Turn off reverse DNS resolution: NMAP performs a Reverse DNS resolution by default, which can slow down the scanning process. You can turn this off using the ‘-n’ option (nmap -n), which eliminates the time spent on name resolution (ITProTV, 2020).
1. Specify the necessary ports: By default, NMAP scans only 1000 most common ports. However, if you know the specific ports you want to scan, specifying them using the ‘p’ option can help speed up the process. For example, to scan only ports 20-25 you would write: nmap -p20-25 (Linuxize, 2019).
1. Use -Pn option (Do not ping): The ‘-Pn’ option treats all hosts as online, skipping the initial ping phase and directly proceeding to the port scanning phase. This option can save a significant amount of time (IONOS, 2020).
1. Parallel scanning: NMAP has a built-in feature that enables it to perform parallel scanning on multiple hosts, hence leading to quicker scan times. Using ‘-iL’ option, you can feed NMAP a list of targets to scan in parallel (HackerTarget.com, 2021).
Sources:
- NMAP.org (2021). “Port Scanning Techniques”. NMAP Network Scanning, [Online]. Available at: https://nmap.org/book/man-port-scanning-techniques.html
- StationX (2018). “NMAP Cheat Sheet: From Discovery to Exploits – Part 1: Introduction to NMAP”, [Online]. Available at: https://www.stationx.net/nmap-cheat-sheet/
- ITProTV (2020). “How to Speed Up NMAP Scans”, [Online]. Available at: https://www.itpro.tv/blog/how-to-speed-up-nmap-scans/
- Linuxize (2019). “How to Use Nmap Command”, [Online]. Available at: https://linuxize.com/post/nmap-command-examples/
- IONOS (2020). “Using Nmap: An Introduction”, [Online]. Available at: https://www.ionos.com/digitalguide/server/tools/nmap-tutorial/
- HackerTarget.com (2021). “NMAP Forged Options”, [Online]. Available at: https://hackertarget.com/nmap-cheatsheet-a-quick-reference-guide/
