ICMP The Internet Control Message Protocol is an integral part of IP designed to facilitate the transmission of notification messages between gateways and source hosts where requests for diagnostic information, support of routing, and as a means of reporting errors in datagram processing are needed. The purpose of these control messages is to provide feedback about problems in the communication environment, and does not guarantee that a datagram will be delivered, or that a control message will be returned.   ICMP (Routing) ICMP Redirect messages represent a common scenario where ICMP is used as a means of facilitating routing functions. In the example, a packet is forwarded to the gateway by host A based on the gateway address of host A. The gateway