Hello, thank you so much for your support Issue is solved   The 9500 is meraki monitored. This action has created the tracking of all the interfaces included the interfaces towards the firewall.   The command looks likes this:   interface port-channel device tracking attach-policy MERAKI_POLICY   With a show device-tracking messages, we can observe packet drop on the port channel between the 9500 and the fortinet       The solution is to apply this on all the interfaces especially on the ports towards the gateway device-tracking attach-policy NOTRACK       The management of the switches is stable now   I'm not sure these tracking commands are useful for the monitoring of core switches.   ... View more