1-11 BPDU Tunneling ConfigurationWhen configuring BPDU tunneling, go to these sections for information you are interested in:z Introduction to BPDU Tunnelingz Configuring BPDU Tunnelingz BPDU Tunneling Configuration ExamplesIntroduction to BPDU TunnelingAs a Layer 2 tunneling technology, BPDU tunneling enables Layer 2 protocol packets fromgeographically dispersed customer networks to be transparently transmitted over specific channelsacross a service provider network.BackgroundCustomers usually use dedicated lines in a service provider network to build their own Layer 2 networks.As a result, very often, a customer network is broken down into parts located at different sides of theservice provider network. As shown in Figure 1-1, User A has two devices: CE 1 and CE 2, both ofwhich belong to VLAN 100. User A’s network is divided into network 1 and network 2, which areconnected by the service provider network. When Layer 2 protocol packets cannot be transparentlytransmitted in the service provider network, User A’s network cannot implement independent Layer 2protocol calculation (for example, STP spanning tree calculation). In this case, the Layer 2 protocolcalculation in User A’s network is mixed with that in the service provider network.Figure 1-1 BPDU tunneling application scenarioISP networkUser A network 1VLAN 100User A network 2VLAN 100CE 1 CE 2PE 1 PE 2With BPDU tunneling, Layer 2 protocol packets from customer networks can be transparentlytransmitted in the service provider network:2) After receiving a Layer 2 protocol packet from User A network 1, PE 1 in the service providernetwork encapsulates the packet, replaces its destination MAC address with a specific multicastMAC address, and then forwards the packet in the service provider network;
