The `-T` option in NMAP is a Timing Template that can be used for specifying the speed at which the network scanning should occur. This is especially crucial for the cybersecurity realm, given the importance of time and speed in various network scanning operations.
NMAP, or Network Mapper, is a free and open-source utility for network discovery and security auditing. It allows system administrators, testers, and other individuals to explore a network, discover hosts, services, and vulnerabilities. The efficiency and speed at which this exploration happens are often determined by the Timing Templates (`-T` option) in NMAP.
Timing Templates allow users to dictate the speed of scanning procedures. This option takes a numerical parameter, ranging from 0 to 5 – each number indicating a different level of scanning speed. There are six predefined timing templates for scanning. We can specify it by using `-T` followed by the number/alias ranging from 0 to 5.
- `-T0` or `paranoid`: This mode is the slowest. Useful when scanning systems that increase a delay upon too many attempts.
- `-T1` or `sneaky`: Slightly faster than the paranoid mode, but still slow.
- `-T2` or `polite`: It limits scanning to less than 1000 packets per second. Networking equipment or hosts likely won’t feel much impact.
- `-T3` or `normal`: NMAP default mode if no other is specified. A balance between speed and avoiding the network congestion.
- `-T4` or `aggressive`: Assumes you’re on a relatively fast and reliable network. This might cause network congestion.
- `-T5` or `insane`: This is the fastest speed, overlooking network congestion and aiming to get results quickest.
Understanding the importance and implications of these timing templates is critical for efficient network scanning and for not raising suspicion or unnecessarily burdening the network. However, the type of timing used during scanning should be configured carefully, as overly aggressive scanning can lead to inaccurate results, network disruptions, or can even be detected as a network attack.
One important consideration when deciding which timing option to use is identifying the stakes involved. For instance, if a high degree of stealth is required, then slower timing options such as `-T0` or `-T1` would likely be employed. Conversely, if speed is the priority, then faster timing options such as `-T4` or `-T5` would be the preferred options.
Sources:
- NMAP Network Scanning: https://nmap.org/book/man-performance.html
- Understanding NMAP Scanning: https://www.giac.org/paper/gsep/6138/understanding-adjusting-nmap-timing-options/104164
- Introduction to NMAP Timing Templates: https://pentest.blog/how-can-i-use-nmap-timing-templates/
