What does a router do when no valid route is found for a packet?

When a router receives a packet but does not have a valid route to the destination, the router’s behavior is to drop the packet. This means that the packet is discarded rather than sent further along the network.

The fundamental role of a router is to direct packets based on their destination IP address, and this process involves consulting its routing table to determine the best path. If the router cannot find a proper entry that outlines where to send the packet, it assumes the destination is unreachable or unknown, and thus the packet is dropped to prevent it from circulating indefinitely or causing routing loops.

This action helps maintain network efficiency and prevents congestion caused by unrouteable packets. Other options, like forwarding the packet to the default gateway or storing the packet for later delivery, are not standard behaviors for routers facing unrouteable packets. These behaviors are more applicable in different contexts, such as protocols or alternative network devices like switches.