The protocol used to send a destination network unknown message back to originating hosts is the Internet Control Message Protocol (ICMP). ICMP is an integral part of the Internet Protocol suite and is primarily responsible for providing feedback, error reporting, and diagnostic information regarding network connectivity.
When a host sends a packet to a destination network, the routing process determines the appropriate path for the packet to reach its destination. If, however, the routing process encounters a situation where it cannot find a valid route for the packet, it generates an ICMP Destination Network Unreachable message. This message is then sent back to the originating host to inform it that the network it is trying to reach is not reachable.
The ICMP Destination Network Unreachable message is part of a larger category of ICMP messages known as "Destination Unreachable" messages. These messages serve to notify the sender about various conditions that prevent successful packet delivery. In the case of the Destination Network Unreachable message, it specifically indicates that the network specified in the packet's destination address cannot be reached.
When the originating host receives the Destination Network Unreachable message, it typically takes appropriate action based on the information provided. This action may involve notifying the application that initiated the communication, attempting to send the packet through an alternate route, or reporting the issue to network administrators for further investigation.
It's important to note that ICMP operates at the network layer of the TCP/IP protocol stack, providing feedback and reporting functionality to IP-based networks. ICMP messages are encapsulated within IP packets and are primarily processed by network devices such as routers and firewalls.
In addition to the Destination Network Unreachable message, ICMP encompasses other message types, including Echo Request and Echo Reply messages (used by the commonly known "ping" utility for network connectivity testing), Time Exceeded messages, Redirect messages, and more. These messages play a crucial role in network troubleshooting, diagnostics, and maintaining proper communication within IP networks.
In conclusion, the Internet Control Message Protocol (ICMP) is the protocol used to send a destination network unknown message back to originating hosts. ICMP provides feedback and error reporting functionality in IP-based networks, and the Destination Network Unreachable message is part of the ICMP protocol suite. It informs the sender that the network specified in the packet's destination address cannot be reached, allowing the originating host to take appropriate action based on the received feedback.
