Question 530
At Seabright Municipal Works, a team reports that it corrected the following problem affecting public service networks and records: A tunnel drops traffic only when behind a NAT device that changes the peer's translated address. Which observation BEST verifies that the correction actually worked?
Explanation
Correct Answer
The VPN remains established through NAT with reliable bidirectional protected flows. This is the decisive evidence for the original problem: A tunnel drops traffic only when behind a NAT device that changes the peer's translated address. It verifies that the intended corrective control—Verify NAT traversal configuration and peer reachability for UDP-encapsulated IPsec—works in the relevant environment; a completed change ticket alone would not prove the outcome at Seabright Municipal Works.
Incorrect Answers
IKE establishes successfully and logs show compatible negotiated parameters. This would be relevant evidence for a different failure: An FTD site-to-site VPN shows no active IKE security association despite route reachability, usually addressed by Inspect IKE proposals, peer identity, authentication, and exchange logs before changing data-plane policy. It does not demonstrate that the current problem at Seabright Municipal Works was resolved. The specific required evidence is: The VPN remains established through NAT with reliable bidirectional protected flows.
Corrected child SAs form and packet encryption and decryption counters increment. This would be relevant evidence for a different failure: IKE succeeds but there are no IPsec child SAs when users send protected traffic, usually addressed by Compare IPsec proposals, traffic selectors, PFS settings, and the actual interesting traffic. It does not demonstrate that the current problem at Seabright Municipal Works was resolved. The specific required evidence is: The VPN remains established through NAT with reliable bidirectional protected flows.
Protected traffic uses the intended encrypted path rather than an ordinary Internet route. This would be relevant evidence for a different failure: Tunnel SAs exist but packets reach a wrong next hop instead of the VPN egress interface, usually addressed by Correct routing and policy-based forwarding toward the appropriate protected tunnel. It does not demonstrate that the current problem at Seabright Municipal Works was resolved. The specific required evidence is: The VPN remains established through NAT with reliable bidirectional protected flows.