102
Configuring BPDU tunneling
Introduction to BPDU tunneling
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 is broken down into parts located at different sides of the service provider network. As
shown in
, User A has two devices (CE 1 and CE 2) and both devices 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, the Layer
2 protocol packets must be transmitted over the service provider network to implement Layer 2 protocol
calculation (for example, spanning tree calculation). 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 calculation.
Figure 36
BPDU tunneling application scenario
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 in the service provider network
encapsulates the packet, replaces its destination MAC address with a specific multicast MAC
address, and then forwards the packet in the service provider network;
2.
The encapsulated Layer 2 protocol packet (called bridge protocol data unit, BPDU) 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.
NOTE:
BPDU tunneling supports the transparent transmission of the Spanning Tree Protocol (STP) packets.
