The first ICMP application program discussed is a simple version of the ping program that is found on almost all
network devices. Ping is an important and fundamental diagnostic tool that tells you whether a network device has
network connectivity and can connect to a particular remote device on the network. The ping program uses the
ICMP Echo Request packet (Type 8) to send a simple message to a remote host. When the remote host receives the
message, it replies with an ICMP Echo Reply packet (Type 0), which contains the original message. Figure 11.2
demonstrates this transaction