icmp - Computer Definition
An extension to the original Internet Protocol (IP) that reports errors that may have occurred in the processing of datagrams. For example, a datagram may be undeliverable or an incorrect route may have been chosen. ICMP supports the testing of a path to a distant host computer through an echo function known as the ping utility. ICMP also supports the requesting of a subnet mask. ICMP is integral to IP and must be implemented in both hosts and routers. See also datagram, echo, host, IP, ping, and utility.
(Internet Control Message Protocol) A TCP/IP protocol used to send error and control messages. For example, a router uses ICMP to notify the sender that its destination node is not available. A ping utility sends ICMP echo requests to verify the existence of an IP address. See Ping of Death and smurf attack.