ICMP Protocol

Internet Control Message Protocol (ICMP) is the protocol responsible for detecting network error conditions and reporting on them. ICMP reports on:

• Dropped packets (when packets are arriving too fast to be processed)

• Connectivity failure (when a destination host can't be reached)

• Redirection (which tells a sending host to use another router)

Chapter 6, Troubleshooting TCP/IP, contains more information on the operating system commands that use ICMP for error detection.