A new firewall policy with NAT enabled appears to work for some destinations but not others, and the administrator suspects the IP pool or outbound interface address is the problem. Using the sniffer and debug flow together, which sequence of observations would correctly prove that the source NAT translation, rather than routing, is causing return traffic to be lost?
- AThe sniffer on the egress interface shows the original client source address leaving unchanged, while debug flow reports a matched policy with NAT applied
- BThe routing-table query lacks a route to the destination, and the sniffer shows no packet leaving any interface for the failing destinations
- CThe debug flow shows the packet matching the policy and being translated to a pool address, and the egress sniffer confirms that translated source, but no reply for that translated address returns Correct
- DThe debug flow reports a reverse path check fail on ingress, and the sniffer shows the SYN never reaching the egress interface
Why A is wrong: If NAT were truly applied, the egress capture would show the translated address, so an unchanged source on the wire contradicts the debug flow claim and points to a capture or interpretation error rather than proving a NAT fault.
Why B is wrong: A missing route with nothing leaving the interface proves a routing failure, not a NAT failure, so this evidence points away from the source NAT hypothesis the question asks to confirm.
Why C is correct: Seeing the translated source leave on the wire confirms NAT happened correctly, so when no reply comes back for that translated address the fault lies in how the upstream handles or routes the pool address, isolating the problem to the NAT translation rather than internal routing.
Why D is wrong: An RPF drop on ingress means the packet is discarded before NAT or egress, so the sniffer correctly shows nothing leaving, but this demonstrates an anti-spoofing routing issue rather than a source NAT translation problem.