Question 370
A site VPN shows repeated authentication failure despite clear IP reachability to the remote headend. Which TWO complementary steps provide the most defensible remediation and its supporting assessment? Select TWO.
Explanation
Correct Answers
Diagnose VPN setup failures in phase order by comparing peer reachability, authentication identities, and mutually supported IKE and IPsec proposals. This control addresses the failure mechanism and narrows the enforcement boundary. Tunnel establishment progresses through distinct authentication and negotiation stages; changing unrelated firewall rules cannot fix mismatched proposals. Confirm pre-change conditions using: Inspect VPN event traces, IKE negotiation state, certificate or PSK errors, UDP 500/4500, and proposal mismatches. This is the implementation portion of the complementary pair. Situation: A site VPN shows repeated authentication failure despite clear IP reachability to the remote headend.
Inspect VPN event traces, IKE negotiation state, certificate or PSK errors, UDP 500/4500, and proposal mismatches. This checks the relevant condition before an engineer modifies production access or detection behavior. Tunnel establishment progresses through distinct authentication and negotiation stages; changing unrelated firewall rules cannot fix mismatched proposals. The controlled response would be: Diagnose VPN setup failures in phase order by comparing peer reachability, authentication identities, and mutually supported IKE and IPsec proposals. This supplies the diagnostic evidence needed for the complementary action. Situation: A site VPN shows repeated authentication failure despite clear IP reachability to the remote headend.
Incorrect Answers
Inspect Access-Request/Accept/Reject behavior, NAS identity, network path, policy rule match, certificates for EAP, and session logs. This step could matter for RADIUS network access troubleshooting but is not part of the required complementary pair for this case. The paired steps are: Diagnose VPN setup failures in phase order by comparing peer reachability, authentication identities, and mutually supported IKE and IPsec proposals. and Inspect VPN event traces, IKE negotiation state, certificate or PSK errors, UDP 500/4500, and proposal mismatches. Situation: A site VPN shows repeated authentication failure despite clear IP reachability to the remote headend.
Tested exploit traffic is detected or blocked by the configured policy while legitimate services remain available. This step could matter for FTD intrusion policy and malware detection but is not part of the required complementary pair for this case. The paired steps are: Diagnose VPN setup failures in phase order by comparing peer reachability, authentication identities, and mutually supported IKE and IPsec proposals. and Inspect VPN event traces, IKE negotiation state, certificate or PSK errors, UDP 500/4500, and proposal mismatches. Situation: A site VPN shows repeated authentication failure despite clear IP reachability to the remote headend.
Trace FTD VPN encryption/decryption counters, routes, NAT exemptions, and ACL matching when IKE is up but applications fail. This step could matter for FTD VPN up but no protected data but is not part of the required complementary pair for this case. The paired steps are: Diagnose VPN setup failures in phase order by comparing peer reachability, authentication identities, and mutually supported IKE and IPsec proposals. and Inspect VPN event traces, IKE negotiation state, certificate or PSK errors, UDP 500/4500, and proposal mismatches. Situation: A site VPN shows repeated authentication failure despite clear IP reachability to the remote headend.


