Quotes About ICMP

commands like ping. As a protocol, ICMP does not rely on TCP or UDP, and it does not use any application layer protocol. It exists as a protocol used to assist IP by helping manage the IP network functions.

Host B can send ICMP echo reply messages to R1's 172.16.4.1 IP address (hosts send echo reply messages to the IP address from which the echo request was received).

Testing using a ping of another device on the LAN can quickly confirm whether the LAN can pass packets and frames. Specifically, a working ping rules out many possible root causes of a problem. For instance, Figure 23-7 shows the ICMP messages that occur if R1 issues the command ping 172.16.1.51, pinging host A, which sits on the same VLAN as R1.