Internet Control Message Protocol (ICMP)

           It is Internet Control Message Protocol. Since IP address does not have in-built mechanism, for           sending error and control messages. It depends on ICMP to provide an error control. ICMP is used for error reporting errors and management queries.

   It is a supporting protocol and used by network devices like routers for sending the error messages and operations information.For example, the requested service is not available or that a host or router could not be reached. ICMP can send the messages only to the source, not to intermediate router. Because the data-gram carries only the addresses of original sender and final destination.  Read more