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 Ethernet ports by default. Use the enable stacking-support command to set the U1 and U2 ports in stacking mode.
When used as Ethernet ports, the U1 and U2 ports can support data rates of 100Gb, 1 x 40Gb, 4 x 25Gb, or 4 x 10Gb using QSFP optics.
When running Fabric Engine, the stacking ports are reserved for use by advanced features on the switch by default. For more information, see the advanced-feature-bandwidth-reservation Boot Flag documentation in the Fabric Engine User Guide for your version of the Fabric Engine operating system.
For information on switch stacking, see Build Stacks.