| 8.1 |  | Overview of TCP/IP Error Message |
| 8.1.2 |  | Error reporting and error correction |

| ICMP is an error reporting protocol for IP. When datagram delivery errors occur, ICMP is used to report these errors back to the source of the datagram. For example, if Workstation 1 in Figure is sending a datagram to Workstation 6, but interface Fa0/0 on Router C goes down, Router C then utilizes ICMP to send a message back to Workstation 1 indicating that the datagram could not be delivered. ICMP does not correct the encountered network problem; it merely reports the problem. When Router C receives the datagram from Workstation 1, it knows only the source and destination IP addresses of the datagram. It does not know about the exact path the datagram took on the way to Router C. Therefore, Router C can only notify Workstation 1 of the failure, and no ICMP messages are sent to Router A and Router B. ICMP reports on the status of the delivered packet only to the source device. It does not propagate information about network changes to routers.
| Web Links Internet Protocol: Error and Control Messages (ICMP) http://faculty.weber.edu/wclark/ch9a.pdf