CISCO CCNA ICMP PING REQUEST

The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet protocol suite. It is chiefly used by networked computers' operating systems to send error messages—indicating, for instance, that a requested service is not available or that a host or router could not be reached.

ICMP differs in purpose from TCP and UDP in that it is not used to send and receive data between end systems. It is usually not used directly by user network applications, with some notable exceptions being the ping tool and traceroute.