Figure 25
Network diagram for BPDU tunneling implementation
As shown in
, the upper part is the service provider network (ISP network), and the lower part
represents two geographically dispersed segments of a customer network: User A network 1 and User A
network 2. Enabling the BPDU tunneling function on the edge devices (PE 1 and PE 2) in the service
provider network allows BPDUs of User A network 1 and User A network 2 to be transparently
transmitted in the service provider network. This ensures consistent spanning tree calculation throughout
User A network, without affecting the spanning 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 the
following workflow.
1.
At the ingress of the service provider network, PE 1 changes the destination MAC address of the
BPDU from 0x0180-C200-0000 to a special multicast MAC address, 0x010F-E200-0003 (the
default multicast MAC address), for example. In the service provider network, the modified BPDU
is 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 MAC
address 0x010F-E200-0003, restores its original destination MAC address 0x0180-C200-0000,
and then sends the BPDU to User A network 2.
NOTE:
Be sure, through configuration, that the VLAN tags carried in BPDUs are neither changed nor removed
during the transparent transmission in the service provider network. Otherwise, the devices in the service
provider network will fail to transparently transmit the customer network BPDUs correctly.
Configuring BPDU tunneling
Configuration prerequisites
Before you configure BPDU tunneling for a protocol, complete 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 connected
port on the CE device to the same VLAN.
•
Configure ports that connect network devices in the service provider network as trunk ports that
allow packets of any VLAN to pass through.
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