The Internet Control Message Protocol (ICMP) is one of the core networking protocols used to run the Internet. ICMP differs from other transport protocols such as UDP and TCP in that it is not usually used to exchange data between systems but instead used as a diagnostic mechanism.
Typical ICMP messages indicate network and server states like that a host could not be reached, a router is down, or a service is unavailable. The vast majority of ICMP activity is completely hidden from the end user, although when performing network diagnostics users frequently interact with ICMP via tools like PING and TRACEROUTE.
- By Jason Fitzpatrick on 01/18/13