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FortiSwitch: Spanning Tree Issue - Port disabled



I have a problem with spanning tree and ports being disabled. I don't know what to do and it is annoying me at times and prevents me from working. Maybe someone has an idea for further debugging.


My client (macOS) is directly connected to a FortiSwitch (124E), which in turn is directly connected to my 40F (trunk). There are some VLAN configured. Occasionally, the port (port20) my client is on gets disabled every few seconds and I lose connectivity.


FortiOS is on 7.0.8 and FortiSwitch 7.0.5. The network setup is very simple.


            +-----------+              +-----------+              +---------+
            |           +--------------+           |              |         |
WAN +-------+    40F    |    TRUNK     |   124E    +--------------+   MAC   |
            |           +--------------+           |              |         |
            +-----------+              +-----------+              +---------+


 The error messages are as follows:


primary switch port port20 has gone down
primary port port20 instance 0 changed role from designated to disabled
primary port port20 instance 0 changed state from forwarding to discarding
primary switch port port20 has come up
primary port port20 instance 0 changed role from disabled to designated



What I have tried so far:


  • Various FortiSwitch port settings (STP, BPDU Guard, Root & Loop Guard, disable, etc.).
  • Disabling the trunk to the FortiGate (connectivity only via one link).
  • set the speed settings to "1Gbits only" or "auto
  • disable the WLAN interface (Ethernet only) on the client
  • various reboots
  • firmware upgrades (FTG and switch)


The error also occurred with other firmware. On the client there is a desktop hypervisor (Fusion) and one VM in bridge mode, but it is disabled. I am not sure if this could have an impact but it does not fit together in time


Any ideas for further debugging?


Thanks in advance.


Nice! I'm glad we narrowed down our problem child! Now time to figure out whether its the OS or a physical issue with the port! That's a bit out of my realm but if you want a second set of eyes, I'd be more than willing to do my best to help!

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