If this are standalone switches (not managed by a FGT) I don't think that they can be stacked. Also the MCLAG is not supported for 1xx series. I guess you could configure LAG for the uplinks in the 1st and 4th switch and leave the interswitch links to be managed by STP.
- Emirjon If you have found a solution, please like and accept it to make it easily accessible for others.
"Stacking" is not supported by FortiSwitches. MCLAG doesn't work to set up mulitple switches to act virtually as one switch. It's a different type of "redundancy" operation of switches. We had the same conversation recently.
Yes they were are communicate with each other. Did run into a weird spanning treee like issue that i had to reboot one of the switches but wasnt that bad. probably coukd have lwt it sit longer but i was impatient. but that was about the biggest issue.
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