Technical Tip: FortiSwitch went offline after FortiGate upgrade to v7.6.1 or later

The issue persists despite the following troubleshooting steps having been done:

• Rebooting FortiSwitch/FortiGate.
• Factory reset FortiSwitch.
• Re-authorized FortiSwitches.
• Disable/enable FortiLink split interface.
• Verify the NTP configuration /time is correct.

Verify the connection by running a packet sniffer on the FortiGate and filtering to port 5246. Only inbound traffic is being received, but there is no response from FortiGate.

The packet sniffer command is as below:

Cameron-kvm05 # diagnose sniffer packet any 'port 5246' 4 0 l

Verify the FortiLink lldp settings.

Cameron-kvm05 # config system interface

Cameron-kvm05 (interface) # edit fortilink

Cameron-kvm05 (fortilink) # show ful | grep lldp

        set lldp-reception vdom

        set lldp-transmission vdom

Workaround:

In the LLDP configuration, enable lldp-reception and lldp-transmission under the FortiLink interface, or rebuild the FortiLink interface.

config system interface

    edit fortilink

        set lldp-reception enable

        set lldp-transmission enable

    end

Related document:

Known issues