Internet Control Message Protocol (ICMP) is a network layer protocol that serves the purpose of error reporting and network path diagnostic functions. The Ping and Traceroute utility tools leverage ICMP messages for fault detection and isolation. ICMP messages are sent using basic IP header. The protocol field in IP header will be set to ICMP followed by the ICMP payload. The ICMP packet has the following format:

The ICMP message types used for network connectivity verification are echo request (Type = 8) and echo reply (Type = 0).