An attacker sends a probe to an IP address to determine if the host is
						alive. Host discovery is one of the earliest phases of network
						reconnaissance. An attacker usually starts with a range of IP addresses
						belonging to a target network and uses various methods to determine if a
						host is present at that IP address. Host discovery is usually referred to as
						'Ping' scanning using a sonar analogy. The goal of the attacker is to send a
						packet through to the IP address and solicit a response from the host. As
						such, a 'ping' can be virtually any crafted packet whatsoever, provided the
						attacker can identify a functional host based on its response. An attack of
						this nature is usually carried out with a 'ping sweep' where a particular
						kind of ping is sent to a range of IP addresses.