One of the basic techniques of identifying a running host is by sending an ICMP ping packet and analyzing the response to draw a conclusion. What if the host or the network is blocking ICMP packets at the network level or the host level? As per the ICMP technique, the host or the network will not pop up in the live host list. Host discovery is one of the core components of a network penetration test or vulnerability scan. A half-done host discovery can ignore hosts or networks from the scope and perform any further operation, thus leaving the network vulnerable.

Nmap provides various options and techniques to identify the live host by sending customized packets to satisfy specific network conditions. If no such options are provided, Nmap by default sends an ICMP echo to identify the live hosts. The provided probe options can be combined to increase...