103Figure 31 BPDU tunneling implementationThe upper section of Figure 31 represents the service provider network (ISP network). The lower section,including User A network 1 and User A network 2, represents the customer networks. Enabling BPDUtunneling on edge devices (PE 1 and PE 2) in the service provider network allows BPDUs of User Anetwork 1 and User A network 2 to be transparently transmitted through the service provider network.This ensures consistent spanning tree calculation throughout User A network, without affecting thespanning tree calculation of the service provider network.Assume that a BPDU is sent from User A network 1 to User A network 2. The BPDU is sent by using thefollowing workflow.1. At the ingress of the service provider network, PE 1 changes the destination MAC address of theBPDU from 0x0180-C200-0000 to a special multicast MAC address, 0x010F-E200-0003 (thedefault multicast MAC address), for example. In the service provider network, the modified BPDUis forwarded as a data packet in the VLAN assigned to User A.2. At the egress of the service provider network, PE 2 recognizes the BPDU with the destination MACaddress 0x010F-E200-0003, restores its original destination MAC address 0x0180-C200-0000,and then sends the BPDU to CE 2.NOTE:Be sure, through configuration, that the VLAN tags carried in BPDUs are neither changed nor removedduring the transparent transmission in the service provider network. Otherwise, the devices in the serviceprovider network will fail to transparently transmit the customer network BPDUs correctly.Configuring BPDU tunnelingConfiguration prerequisitesBefore configuring BPDU tunneling for a protocol, perform the following tasks:• Enable the protocol in the customer network.• Assign the port on which you want to enable BPDU tunneling on the PE device and the connectedport on the CE device to the same VLAN.• Configure ports that connect network devices in the service provider network as trunk ports thatallow packets of any VLAN to pass through.
