3Com Switch 8800 Advanced Software V5 Configuration Guide

150 CHAPTER 13: BPDU TUNNELING CONFIGURATION
BPDU isolation
When a port receives BPDUs of other networks, the port will discard the BPDUs, so
that they will not take part in spanning tree calculation. Refer to
“Configuring
BPDU Isolation” on page 150.
BPDU transparent transmission
As shown in Figure 41, the upper part is the service provider network, and the
lower part represents the customer networks. The customer networks include
network A and network B. Enabling the BPDU tunneling function on the BPDU
input/output devices across the service provider network allows BPDUs of the
customer networks to be transparently transmitted in the service provider
network, and allows each customer network to implement independent spanning
tree calculation, without interfering each other. Refer to
“Configuring BPDU
Transparent Transmission” on page 151.
Figure 41 Network hierarchy of BPDU tunneling
The BPDU packet is processed in the operator network as follows:
■ At the BPDU input side, the device changes the destination MAC address of a
BPDU from a customer network from 0x0180-C200-0000 to a special multicast
MAC address, 0x0100-0CCD-CDD0. In the service provider’s network, the
modified BPDUs are forwarded as data packets in the user VLAN.
■ At the packet output side, the device recognizes the BPDU with the destination
MAC address of 0x0100-0CCD-CDD0 and restores its original destination MAC
address 0x0180-C200-0000. Then, the device removes the out-layer VLAN tag,
and sends the BPDU to the destination customer network.
n
Make sure, through configuration, that the VLAN tag of the BPDU is neither
changed nor removed during its transparent transmission in the service provider
network; otherwise, the system will fail to transparently transmit the customer
network BPDU correctly.
Configuring BPDU
Isolation
Perform the following tasks to configure BPDU isolation:
Network
Network B
Network A
Service provider
network
Customer
networks
BPDU input /output
device
BPDU input/output
device