When a router is unable to find a known route in the routing table, how does it handle the packet?

Question:
When a router is unable to find a known route in the routing table, how does it handle the packet?

• It discards the packet
• It sends the packet over the route with the best metric
• It sends the packet to the next hop address
• It sends the packet to the gateway of last resort

Explanation: In fact this question is not clear. If we understand that “router is unable to find a known route in the routing table” and there is no default route in the routing table then the router will surely discard the packet -> A is correct. But we are not sure if there is a default route or not so let learn more about gateway of last resort.

A Gateway of Last Resort is a route used by the router when no other known route exists to send the IP packet. For CCNA level, when ip routing feature is enabled, a gateway of last resort is usually created by:
+ The “ip default-network” command (but dynamic routing protocols have different behaviors). But in general, the “ip default-network” cannot set the gateway of last resort without a known route in the routing table.
+ Creating a static route to network 0.0.0.0 0.0.0.0 is another way to set the gateway of last resort on a router. This is the reason why this question is not clear as it does not tell us if a default route exists or not.

Maybe in this question a default route does not exist. Otherwise the author would notice and indicate it in the question.

For more information about Gateway of Last Resort, please read:

http://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/16448-default.html

Exam with this question: CCNA v3.0 (200-125) Study Guide – Exam Dumps