This object identifies which bridge, numbered 1 through 32, or the special backbone or beb, backbone edge bridge, designation, a C-VLAN registration table entry belongs to. As part of the table's index, it lets an admin distinguish C-VLAN registration entries that apply to different provider-bridge components within a single device, such as separating customer-facing bridges from the backbone bridge. An admin inspecting C-VLAN registrations for the backbone edge bridge component would look for entries where this object reports beb rather than a numeric bridge index.