300-320 Question #439: Real Exam Question with Answer & Explanation

The correct answer is B: The packet is forwarded because it arrived on the interface used to route traffic back to the. This question refers to RPF (Reverse Path Forwarding), a spoofing-prevention mechanism. An RPF check examines whether an incoming packet arrived on the interface that the router would use to route traffic back to the packet's source IP address. A successful RPF check means the pa

Question

What is the result of a successful RFP check?

Options

AThe packet is dropped because it arrived on the interface used to route traffic back to the
BThe packet is forwarded because it arrived on the interface used to route traffic back to the
CThe packet is forwarded because it arrived on the interface used to route traffic to the
DThe packet is dropped because it arrived on the interface used to route traffic to the

Explanation

This question refers to RPF (Reverse Path Forwarding), a spoofing-prevention mechanism. An RPF check examines whether an incoming packet arrived on the interface that the router would use to route traffic back to the packet's source IP address. A successful RPF check means the packet did arrive on the expected (correct) interface, indicating the source address is reachable via that interface and is likely not spoofed. The result is that the packet is forwarded. A failed RPF check (packet arrived on the wrong interface) results in the packet being dropped as a potential spoofed or asymmetrically routed packet. Option B correctly states the packet is forwarded because it arrived on the interface used to route back to the source.

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