The Universal Ethernet ports, or stacking ports, are located on the front panel of the switch and are labeled U1 and U2. These ports can be used with Switch Engine as stacking ports, or as Ethernet ports with Switch Engine and Fabric Engine in non-fabric mode (Fabric Engine does not support stacking).
The Universal Ethernet ports operate as stacking ports by default. Use the disable stacking-support command to set the U1 and U2 ports in Ethernet mode.
When used as Ethernet ports, the U1 and U2 ports support data rates of either 10Gb using SFP+ optics or 20Gb using SFP-DD optics. 5420M switch models support two 10Gb channels on each SFP-DD port when the ports are used as Ethernet ports on Switch Engine 31.6 and later. 5420F switch models support one 10Gb channel on each SFP-DD port when the ports are used as Ethernet ports.
For information on switch stacking, see Build Stacks.