Huawei quidway s7700 - Overview of Layer 2 Protocol Transparent Transmission

11.1 Overview of Layer 2 Protocol Transparent
Transmission
This section describes the concept of Layer 2 protocol transparent transmission.
Background
In certain network environments, packets of Layer 2 protocols such as MSTP, HGMP, and LACP
need to be transmitted between user networks across the backbone network to complete
calculation of the protocols.
As shown in Figure 11-1, user network 1 and user network 2 run Layer 2 protocols, for example,
MSTP. Layer 2 protocol packets of user network 1 must traverse the backbone network to reach
user network 2 so that the spanning tree can be calculated. Packets of a Layer 2 protocol usually
use the same destination MAC address. For example, MSTP packets are BPDUs that use 0180-
C200-0000 as the destination MAC address. Therefore, when the BPDUs reach a PE on the
backbone network, the PE cannot identify whether the BPDUs are sent from a user network or
the backbone network. As a result, the PE sends the BPDUs to the CPU for spanning tree
calculation.
In this case, the spanning tree is calculated between the devices of user network 1 and PE1, and
the devices of user network 2 are not involved in the calculation. Therefore, BPDUs of user
network 1 cannot be sent to user network 2 through the backbone network.
Figure 11-1 Transparent transmission of Layer 2 protocol packets on an ISP network
ISP
network
User
network1
User
network2
CE1
CE2
PE1 PE2
Layer 2 protocol transparent transmission can solve this problem.
To transparently transmit Layer 2 protocol packets on the backbone network, the following
requirements must be met:
Quidway S7700 Smart Routing Switch
Configuration Guide - Ethernet 11 Layer 2 Protocol Transparent Transmission Configuration
Issue 01 (2011-07-15) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
571