The issue described pertains to the establishment of a tunnel (likely a CAPWAP tunnel for

management purposes between FortiGate and FortiSwitch). Based on typical error analysis in tunnel

setup scenarios:

The CAPWAP tunnel failed to come up due to a mismatch in time (Option C): This answer is plausible

because time synchronization is crucial for security protocols that underpin tunnel establishments,

such as DTLS (Datagram Transport Layer Security) used within CAPWAP tunnels. If the clocks on

FortiGate and FortiSwitch are significantly out of sync, the security handshake (which can include

timestamp validation) could fail, preventing the tunnel from coming up.

Reference:

Fortinet's technical documentation typically outlines the importance of time synchronization for

secure communications. In CAPWAP/DLTS scenarios, precise time matching is crucial to ensure that

the cryptographic parameters align correctly during the handshake process.