An attacker sends out an ICMP Type 8 Echo Request, commonly known as a
						'Ping', in order to determine if a target system is responsive. If the
						request is not blocked by a firewall or ACL, the target host will respond
						with an ICMP Type 0 Echo Reply datagram. This type of exchange is usually
						referred to as a 'Ping' due to the Ping utility present in almost all
						operating systems. Ping, as commonly implemented, allows a user to test for
						alive hosts, measure round-trip time, and measure the percentage of packet
						loss. Performing this operation for a range of hosts on the network is known
						as a 'Ping Sweep'. While the Ping utility is useful for small-scale host
						discovery, it was not designed for rapid or efficient host discovery over
						large network blocks. Other scanning utilities have been created that make
						ICMP ping sweeps easier to perform. Most networks filter ingress ICMP Type 8
						messages for security reasons. Various other methods of performing ping
						sweeps have developed as a result. It is important to recognise the key
						security goal of the attacker is to discover if an IP address is alive, or
						has a responsive host. To this end, virtually any type of ICMP message, as
						defined by RFC 792 is useful. An attacker can cycle through various types of
						ICMP messages to determine if holes exist in the firewall configuration.
						When ICMP ping sweeps fail to discover hosts, other protocols can be used
						for the same purpose, such as TCP SYN or ACK segments, UDP datagrams sent to
						closed ports, etc. The attackers goal is to discover as many potential
						targets as possible can utilise a wide range of techniques to achieve this
						end. ICMP pings have the following characteristics:1. Host Discovery: Can be used to discover if a host is alive via ICMP
							Echo Reply Message2. Effective Against: LANs or Internal IP address ranges where
							firewall or ACL rules are less restrictive3. Weak Against: Firewalls properly configured to block ICMP Echo
							Request and Echo Replies.4. Port State: Unable to determine the status of ports on a
							host.