i am facing one of the strange issue with FortiGate 401F model it run Firmware Version 7.0.12.
suddenly sometimes this FortiGate stop working even i can not access internal corporate subnets and internet but when i am checking 184.108.40.206 from FortiGate firewall Console i can reach to 220.127.116.11 but client can not ping 18.104.22.168 and can't brows to the internet.
i was opened TT with FortiGate Tach still they are also looking for this issue this issue happen sometime in a week two times and sometime in a month.
i troubleshoot allot and check the internal network after troubleshooting the last thing which i did it was i configure on of the physical port of the FortiGate to check and allow that test subnet to internet for testing purpose when this issue happen i connect my laptop direct to that test port but i had no internet so due to that i figure out that issue is with FortiGate firewall becouse even direct from FortiGate i dont had internet, during this period of time even i can not reach my internal subnets as well, it down the functioning for 5 minuets after 5 minuets everting coming up and working.
As Suraj suggested, you can check if there were crashes or not. Additionally, you can run a debug flow while pinging across the internal network or to the Internet to see the traffic flow. Below are debug flow commands. You can replace IP address with a destination IP.
di deb disable di deb res diagnose debug flow filter clear di deb flow filter addr 10.0.2.5 di deb flow filter proto 1 diagnose debug flow show function-name enable di deb flow show iprope en diagnose debug console timestamp enable diagnose debug flow trace start 500 diagnose debug enable
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