Dell PowerEdge M420 Configuration Manual page 138

NOTE:
The PowerConnect M6348 and M6220 can not be stacked together.
1 For each switch in the stack, connect one of the short stacking cables from
stacking port one on the switch to stacking port two on the next switch.
2 If necessary, use a separately purchased, long (3 meter) stacking cable to
connect the switches. Repeat this process until all of the devices are
connected.
3 Use the remaining stacking cable to connect the remaining free ports, from
port one of the last switch to port two of the first switch.
Figure 8-2. Connecting a Stack of PowerConnect M6348 Switches
138
Managing a Switch Stack
upper and lower
stacking ports
stacking cable