Question 450
Two peers repeatedly establish Phase 1 then log Phase 2 NO_PROPOSAL_CHOSEN errors; administrators waste time changing firewall address objects instead of matching proposals. Which diagnostic evidence should the FortiGate administrator check FIRST?
Explanation
Correct Answer
Collect scoped IKE debug, vpn tunnel list state, security association counters, phase proposal messages, tunnel route, session table and forward/reverse packet captures. This distinguishes the relevant FortiGate device, session or controller evidence. An IKE SA in established state does not prove any user payload crossed the tunnel, and generic ping failure can arise from routes or firewall rules after both phases succeed. The corresponding action is: Diagnose FortiOS IPsec connectivity by separating interface transport, IKE Phase 1 authentication, Phase 2 negotiation, routed packet selection and firewall policy outcomes. Scenario: Two peers repeatedly establish Phase 1 then log Phase 2 NO_PROPOSAL_CHOSEN errors; administrators waste time changing firewall address objects instead of matching proposals.
Incorrect Answers
Compare connected PoP, endpoint tunnel state, DNS resolution, traffic steering mode, cloud security inspection result, private-app connector health and remote-user event logs. This diagnostic is related to FortiSASE PoP policy steering and remote diagnostics rather than the controlling evidence for this scenario. Examine instead: Collect scoped IKE debug, vpn tunnel list state, security association counters, phase proposal messages, tunnel route, session table and forward/reverse packet captures. Scenario: Two peers repeatedly establish Phase 1 then log Phase 2 NO_PROPOSAL_CHOSEN errors; administrators waste time changing firewall address objects instead of matching proposals.
Read diagnose hardware sysinfo mem, process memory distribution, session counts, conserve-mode events and affected security profile actions. This diagnostic is related to FortiGate memory pressure and conserve-mode diagnosis rather than the controlling evidence for this scenario. Examine instead: Collect scoped IKE debug, vpn tunnel list state, security association counters, phase proposal messages, tunnel route, session table and forward/reverse packet captures. Scenario: Two peers repeatedly establish Phase 1 then log Phase 2 NO_PROPOSAL_CHOSEN errors; administrators waste time changing firewall address objects instead of matching proposals.
Inspect peer NAT detection, outer public addresses and ports, IKE 500/4500 flows, upstream firewall rules, mapped address stability and peer debug logs. This diagnostic is related to IPsec NAT traversal with upstream address translation rather than the controlling evidence for this scenario. Examine instead: Collect scoped IKE debug, vpn tunnel list state, security association counters, phase proposal messages, tunnel route, session table and forward/reverse packet captures. Scenario: Two peers repeatedly establish Phase 1 then log Phase 2 NO_PROPOSAL_CHOSEN errors; administrators waste time changing firewall address objects instead of matching proposals.