H3C Technologies H3C WX5500E Series Access Controllers - Manual (Page 113)

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Configuring BPDU tunneling
This chapter describes how to configure BPDU tunneling.
Overview
As a Layer 2 tunneling technology, BPDU tunneling enables Layer 2 protocol packets from
geographically dispersed customer networks to be transparently transmitted over specific tunnels across
a service provider network.
Background
Dedicated lines are used in a service provider network to build user-specific Layer 2 networks. As a result,
a user network consists of parts located at different sides of the service provider network. As shown
in Figure 28 , the devices of User A are CE 1 and CE 2, which both belong to VLAN 100. User A's
network is divided into network 1 and network 2, which are connected by the service provider network.
When a Layer 2 protocol (for example, STP) runs on both network 1 and network 2, Layer 2 protocol
packets must be transmitted over the service provider network to implement Layer 2 protocol calculations
(for example, spanning tree calculations). When receiving a Layer 2 protocol packet, the PEs cannot
determine whether the packet is from the user network or the service provider network, and must deliver
the packet to the CPU for processing. In this case, the Layer 2 protocol calculation in User A's network is
mixed with that in the service provider network, and the user network cannot implement independent
Layer 2 protocol calculations.
Figure 28 BPDU tunneling application scenario
BPDU tunneling addresses this problem. With BPDU tunneling, Layer 2 protocol packets from customer
networks can be transparently transmitted over the service provider network in the following workflow:
1. After receiving a Layer 2 protocol packet from CE 1, PE 1 encapsulates the packet, replaces its
destination MAC address with a specific multicast MAC address, and forwards the packet to the
service provider network.
2. The encapsulated Layer 2 protocol packet (called a bridge protocol data unit) is forwarded to PE
2 at the other end of the service provider network, which de-encapsulates the packet, restores the
original destination MAC address of the packet, and then sends the packet to CE 2.
H3C devices support BPDU tunneling for the following protocols: