This object selects which multicast MAC address GVRP uses for its BPDUs on network-to-network interfaces in a service-provider deployment: the standard 802.1d GVRP address 01:80:CC:00:00:21, or the 802.1ad address 01:80:CC:00:00:0D. Admins set this to match the GVRP addressing scheme used by the carrier's provider-bridge network, since interoperability requires both ends to send and listen for GVRP frames on the same destination MAC. For example, an operator running an 802.1ad tunnel to a provider network would set this to 'dot1ad' so its GVRP BPDUs use 01:80:CC:00:00:0D instead of the customer-side default.