ExtremeSwitching series switches, whether or not included in a SummitStack, require a loopback port for certain configurations. If two or more subscriber VLANs have overlapping ports (where the same ports are assigned to both VLANs), each of the subscriber VLANs with overlapping ports must have a dedicated loopback port.
The loopback port can be added when the subscriber VLAN is added to the PVLAN.
If you need to add a loopback port to an existing subscriber VLAN, use the following command:
configure {vlan} vlan_name vlan-translation add loopback-port port