MA-CBL-40G is a stacking cable and should be used to stack switches. The MS450 needs these stacking cables: MA-CBL-100G (MA-CBL-40 i not supported) The MS390 needs these: MA-CBL-120G In the uplink module ports of the MS390 and the ports on the 450 you would need the approriate SFPs for the fiber cables you need. Typically either SR/LR or MM/SM
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