Nmap, or Network Mapper, is a free and open-source tool that is typically used for security auditing, network exploration, and vulnerability detection. However, its potential to create ‘noise’ or a significant amount of information traffic during scanning means that it can unintentionally alert the network’s Intrusion Detection System (IDS). Hence, an appropriate question is how to carry out an Nmap analysis with a minimum amount of noise.
There are several ways to conduct an NMAP analysis with as little noise as possible. Here are some common methods:
1. Slow Down the Scan: If you dictate Nmap to scan slowly, it will create less traffic, allowing it to slip under the radar. This achievement can be done using the “-T” option followed by a number from 0 (slowest) to 5 (fastest). Hence, “-T0” would be the slowest scan, generating the least amount of noise (source: Nmap Network Scanning, Fyodor, 2009).
1. Idle Scan (“-sI”): This method is one of the stealthiest, as it involves using a ‘zombie’ host to perform the scan, making it difficult to detect. However, it’s worth noting that this technique requires a particular set of conditions to be met, including finding an appropriate ‘zombie’ host (source: Nmap Network Scanning, Fyodor, 2009).
1. Fragmented IP Packets (“-f”): This option causes Nmap to send each packet as several smaller, ‘fragmented’ packets, confusing and evading simple packet filters (source: Nmap Network Scanning, Fyodor, 2009).
1. Decoy (“-D”): This technique involves sending ‘decoy’ IP addresses to create distractions within the noise, making it difficult for the target to find the real scanning system. The Nmap syntax for this is “-D RND:10 [target]” which creates random decoy addresses.
1. Use the Stealth Scanning Method (“-sS”): This method involves sending a SYN packet and waiting for a response. If a SYN/ACK is received, Nmap understands the port is open but never completes the TCP handshake, hence lowering the noise level.
A couple of online sources that provide excellent guidance on how to conduct low-noise Nmap scans can be found on NMAP’s official repository (https://nmap.org/book/man-bypass-firewalls-ids.html), and they even have a book authored by the creator of NMAP, Fyodor, titled “Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning”. Another example is the “Nmap Cookbook: The Fat-free Guide to Network Scanning” by Nicholas Marsh.
Remember, however, that these tactics often trade speed and accuracy for stealth. A slow scan, for example, might provide less noise but will take longer to complete.
And it is also important to note that ethical considerations and legality shall always be taken into account when conducting any form of network analysis, ensuring you have appropriate permissions before initiating any Nmap scan.
