ICMP- Internet Control Message Protocol
The Internet Control Message Protocol (ICMP) is defined by IETF RFC972. ICMP messages generally contain information about routing difficulties with IP datagrams or simple exchange such as timestamp or echo transactions.
Computer systems deliver and receive data with the TCP/IP protocol. When there’s an issue with the link, error and status messages concerning the link are send using ICMP, which is part of their internet protocol. It’s a supportive protocol and utilized by networks devices such as routers for sending the error messages and operations instruction.
ICMP uses the Packet Internet Grope (PING) utility to test the network layer connectivity by sending the ICMP echo to the destination. The reachability is measured either by its ICMP echo replay or its response code.
Host A sends an ARP request to the switch to identify the MAC address of host B. Once the address is learnt, Host A sends an ICMP echo to verify the reachability to host B
Host B receives the ICMP echo and sends an echo replay which shows the reachability between Host A and Host B.