(ICMP) A part of IP that handles error & control messages. It is used by gateways & hosts to report problems with the datagram to the original source. ICMP also has an echo request/reply feature used to test whether a node is alive or dead.
This is an extension to the internet protocol, which supports error and control messaging. See Transmission Control Protocol/Internet Protocol (TCP/IP).
The Internet Control Message Protocol handles the sending of error messages as well as test and information packets, and it is part of TCP/IP.