Question 560
A partner renews its IPsec certificate under a new intermediate CA, and the local FortiGate rejects the IKE signature because its trusted chain was not updated. Which diagnostic evidence should the FortiGate administrator check FIRST?
Explanation
Correct Answer
Check VPN certificate subject/SAN, CA trust chain, CRL availability, peer ID matching, validity dates, IKE authentication events and SA rekey statistics. This distinguishes the relevant FortiGate device, session or controller evidence. Disabling certificate or peer identity verification may bring a tunnel up but defeats authentication, and scheduled IKE/ESP rekey depends on both ends agreeing on proposals. The corresponding action is: Use appropriate certificate trust, subject identity and revocation or PSK rotation controls for FortiGate site-to-site IPsec, and verify rekey without disabling peer validation. Scenario: A partner renews its IPsec certificate under a new intermediate CA, and the local FortiGate rejects the IKE signature because its trusted chain was not updated.
Incorrect Answers
Collect scoped IKE debug, vpn tunnel list state, security association counters, phase proposal messages, tunnel route, session table and forward/reverse packet captures. This diagnostic is related to IKE and IPsec debug evidence for Phase 1 versus child-SA failures rather than the controlling evidence for this scenario. Examine instead: Check VPN certificate subject/SAN, CA trust chain, CRL availability, peer ID matching, validity dates, IKE authentication events and SA rekey statistics. Scenario: A partner renews its IPsec certificate under a new intermediate CA, and the local FortiGate rejects the IKE signature because its trusted chain was not updated.
Examine source/destination firewall policy, SD-WAN zone, NAT behavior, explicit policy routes, application signature, health check and session egress. This diagnostic is related to SD-WAN interactions with firewall policies and source-specific routes rather than the controlling evidence for this scenario. Examine instead: Check VPN certificate subject/SAN, CA trust chain, CRL availability, peer ID matching, validity dates, IKE authentication events and SA rekey statistics. Scenario: A partner renews its IPsec certificate under a new intermediate CA, and the local FortiGate rejects the IKE signature because its trusted chain was not updated.
Check client DNS answer, ingress/internal interfaces, VIP external address match, matched firewall policy, reverse session and asymmetric return packets. This diagnostic is related to NAT hairpin and internal use of public VIP names rather than the controlling evidence for this scenario. Examine instead: Check VPN certificate subject/SAN, CA trust chain, CRL availability, peer ID matching, validity dates, IKE authentication events and SA rekey statistics. Scenario: A partner renews its IPsec certificate under a new intermediate CA, and the local FortiGate rejects the IKE signature because its trusted chain was not updated.