Question 640
A tunnel dashboard shows connected but encrypt counters rise while decrypt counters remain zero. Which Cisco security control or operational response BEST addresses the stated need?
Explanation
Correct Answer
Trace FTD VPN encryption/decryption counters, routes, NAT exemptions, and ACL matching when IKE is up but applications fail. This control addresses the failure mechanism and narrows the enforcement boundary. IKE-up status validates part of the control plane; the protected data plane requires matching routes, selectors, and NAT behavior. Confirm pre-change conditions using: Inspect bidirectional security association counters, packet traces, NAT policy, route selection, and remote selectors. Situation: A tunnel dashboard shows connected but encrypt counters rise while decrypt counters remain zero.
Incorrect Answers
Trace RADIUS network-access request and decision paths to isolate credential, shared secret, policy, or reachability failures. This response applies to RADIUS network access troubleshooting, not the controlling requirement in this case. RADIUS typically supports network access control and policy attributes; network reachability, policy, and EAP trust must be checked independently. For this scenario, the targeted action is: Trace FTD VPN encryption/decryption counters, routes, NAT exemptions, and ACL matching when IKE is up but applications fail. Situation: A tunnel dashboard shows connected but encrypt counters rise while decrypt counters remain zero.
Configure FTD site-to-site VPN using compatible peer parameters, network selectors, identities, and routing/access rules, then verify both tunnel phases. This response applies to FTD site-to-site VPN crypto policy, not the controlling requirement in this case. Successful VPN peer authentication does not prove application forwarding; selectors, route tables, NAT, and access policies also govern data traffic. For this scenario, the targeted action is: Trace FTD VPN encryption/decryption counters, routes, NAT exemptions, and ACL matching when IKE is up but applications fail. Situation: A tunnel dashboard shows connected but encrypt counters rise while decrypt counters remain zero.
Diagnose VPN setup failures in phase order by comparing peer reachability, authentication identities, and mutually supported IKE and IPsec proposals. This response applies to FTD IKE negotiation failure isolation, not the controlling requirement in this case. Tunnel establishment progresses through distinct authentication and negotiation stages; changing unrelated firewall rules cannot fix mismatched proposals. For this scenario, the targeted action is: Trace FTD VPN encryption/decryption counters, routes, NAT exemptions, and ACL matching when IKE is up but applications fail. Situation: A tunnel dashboard shows connected but encrypt counters rise while decrypt counters remain zero.


