Application Scenarios for Layer 2 Protocol Tunneling
As shown in Figure 1, CE1 and CE2 are edge devices on private networks of User A in different locations. The two private networks connect to the ISP network through PE1 and PE2. Networks of User A have redundant links, so MSTP is used to remove loops on the Layer 2 network. When MSTP packets sent by CEs reach PEs, PEs send the packets to the CPUs for processing because they cannot identify the network that MSTP packets come from. Layer 2 protocol calculations on the user network and ISP network affect each other and cannot be implemented independently.
You can configure Layer 2 protocol tunneling on PEs, so that MSTP packets are not sent to the CPUs of PEs for processing. This prevents PEs from participating in spanning tree calculation.
