FortiGates with ULL ports may expereince status down on active ports

After upgrading to FortiOS version 7.2.9, FortiGate platforms with ultra-low-latency (ULL) ports like 600F and 901G models may experience link status down on active ULL ports if the following conditions are met:

• The ULL port is set to 25G mode

• Forward error correcting (FEC) is enabled on the port

• Forward error correcting (FEC) is disabled on the connecting switch

This behaviour change is due to a fix in FortiOS 7.2.9 version for an issue where FEC feature was disabled even though it was enabled in the CLI. This allowed the FortiGate ULL port to still connect to the switch with FEC disabled. After the fix, FEC is activated on the ForitGate and caused a mismatch with the switch.

Workaround: User can disable FEC feature on the FortiGate ULL port to match with the connecting switch, or they can enable FEC feature on the switch to match with the FortiGate side.

config system interface
    edit <ULL port>
        set forward-error-correction disable
    next
end