Alcatel-Lucent NRS I – Interior Routing Protocols and High Availability — Question 5

When a router receives an IP packet, but does not find a match in the routing table for the destination IP address, what actions are performed by the router?

Answer options

• A. The packet is flooded out all router interfaces.
• B. The packet is dropped and an ICMP unreachable message is sent back to the source.
• C. The packet is silently discarded.
• D. The packet is flooded out all interfaces and an ICMP unreachable message is sent.

Correct answer: B

Explanation

The correct answer is B because when a router cannot find a route for a destination IP, it drops the packet and notifies the sender with an ICMP unreachable message. Option A is incorrect because flooding the packet would be inappropriate without a route. Option C is also wrong since it does not provide feedback to the sender, and D incorrectly states that an ICMP message is sent when the packet is flooded.