A router has a full routing table but receives a packet destined for a public address that matches no specific entry. The output shows the line: Gateway of last resort is 203.0.113.1 to network 0.0.0.0. What does the gateway of last resort tell the router to do with this packet?
- ADrop the packet and send an ICMP unreachable, because a gateway of last resort means routing has failed.
- BFlood the packet out every interface, because the destination is unknown and must be discovered.
- CBuffer the packet until a more specific route is learned for the destination network.
- DForward the packet using the default route toward 203.0.113.1, because no more specific prefix matches the destination. Correct
Why A is wrong: A configured gateway of last resort is the opposite of failure: it provides a catch-all next hop. The router only drops and signals unreachable when there is no default route at all.
Why B is wrong: Routers never flood unknown unicasts; that is switch behaviour for unknown MAC addresses. A router with a default route forwards the packet to the single gateway of last resort.
Why C is wrong: A router does not hold packets waiting for a better route. If a default route exists it forwards immediately to the gateway of last resort rather than buffering.
Why D is correct: The gateway of last resort identifies the next hop for the default route 0.0.0.0/0. When longest prefix match finds no more specific entry, the router uses this default and forwards toward 203.0.113.1.