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Chapter 15 bpdu-tunnel Configuration
15.1 Introduction to bpdu-tunnel
BPDU Tunnel is a Layer 2 tunnel technology. It allows Layer 2 protocol packets of
geographically dispersed private network users to be transparently transmitted over specific
tunnels across a service provider network.
15.1.1 bpdu-tunnel function
In MAN application, multi-branches of a corporation may connect with each other by the
service provider network. VPN provided by the service provider enables the geographically
dispersed networks to form a local LAN, so the service provider needs to provide the tunnel
function, namely, data information generated by user’s network is able to inextenso arrive at
other networks of the same corporation through the service provider network. To maintain a
local concept, it not only needs to transmit the data within the user’s private network across the
tunnel, but also transmit layer 2 protocol packets within the user’s private network.
15.1.2 Background of bpdu-tunnel
Special 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 Figure, User A has two devices (CE 1 and CE 2) and both
devices belong to the same VLAN. User’s network is divided into network 1 and network 2,
which are connected by the service provider network. When Layer 2 protocol packets cannot
implement the passthrough across the service provider network, the user’s network cannot
process independent Layer 2 protocol calculation (for example, spanning tree calculation), so
they affect each other.