If a router does not know where to forward a packet, what does it do with the packet?

• A. Discards it
• B. Forwards to all interfaces
• C. Sends to default gateway
• D. Encrypts it

Answer: (A)

When a router handles a packet, it first checks its routing table to find the next hop for the destination. If there is no entry that matches the destination, the router has no path to forward the packet. In this situation, the correct action is to drop the packet so it isn’t sent into the network without a known route. Some devices may also send back an ICMP Destination Unreachable message to inform the sender, but the essential behavior is to discard when no route exists.

The other options don’t fit: forwarding to all interfaces would cause unnecessary broadcast traffic and potential loops; sending to a default gateway only happens if a default route exists, which isn’t guaranteed when no route is known; encryption has no role in deciding how to forward or drop a packet.