Replacing Cisco CBS350X Stack with 2x FortiSwitch 448E

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Hi everyone,

I'm currently working with the following setup:

• We have a FortiGate 100F

• Port X1 on the FortiGate connects via 10G to a stack of 2x Cisco CBS350X (on the Ground Floor).

• From there, there's an uplink via 10G to another stack of 2x Cisco CBS350X (on the Upper Floor).
  The reason for using the stack is to expand port availability, not for redundancy.

Now, I want to replace the Cisco stack on the Ground Floor with 2x FortiSwitch 448E but leave the stack in the Upper floor.

What would be the most sensible and correct way here?
Can the 448E also be operated in a stack?
Does it make sense to connect X1 and X2 to a 448E each? And to connect both 448E to the respective CBS350X on the upper floor?

Thanks in advance for your help!

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@AEK 
understand, but again I don't need a Trunk (LCAP) configuration from my 2x448E in the ground floor, to my new 2x448E in the upper floor?
Like what I have at the moment to my 2x cisco in the upper floor?