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

[achu]

Description	The article describes that the FortiSwitches go offline after upgrading FortiGate when the LLDP settings are set to VDOM  or disabled in the FortiLink interface. The issue may be caused by a bug detected in v7.6.1 or later.
Scope	FortiGate v7.6.1 or later.
Solution	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