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). A stack can be created either with native stacking or with alternate stacking.
In native stacking, switches are connected using either designated Ethernet data ports or dedicated stacking connectors. 7720 Series switches support native stacking with data rates of 100Gbps using the default Native V400 or Native V400 Alternative Configuration stacking methods. The stacking ports on 7720-32C models are ports 31 and 32.
In alternate stacking, switches are connected using 10-Gbps Ethernet data ports that have been configured for stacking. These ports are located either on the switch itself or on option cards installed on either the front or the rear of the switch. 7720 does not support alternate 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, 2 x 50Gb (Switch Engine only), 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.