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S12700 V200R012C00 Configuration Guide - Ethernet Switching

This document describes the configuration of Ethernet services, including configuring MAC address table, link aggregation, VLANs, VLAN aggregation, MUX VLAN, VLAN termination, Voice VLAN, VLAN mapping, QinQ, GVRP, VCMP, STP/RSTP/MSTP, VBST, SEP, RRPP, ERPS, LBDT, and Layer 2 protocol transparent transmission.
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Overview of Layer 2 Protocol Transparent Transmission

Overview of Layer 2 Protocol Transparent Transmission


Layer 2 protocol transparent transmission is a Layer 2 tunneling technology that transparently transmits BPDUs between private networks at different locations over a specified tunnel on a public Internet Service Provider (ISP) network.


Leased lines of ISPs are often used to establish Layer 2 networks. As a result, private user networks can be located at two sides of ISP networks. In Figure 21-1, User A has two networks: network1 and network2. The two networks are connected through the ISP network. When network1 and network2 run the same Layer 2 protocol (such as MSTP), Layer 2 protocol packets from network1 and network2 must be transmitted through the ISP network to perform Layer 2 protocol calculation (for example, calculating a spanning tree). Generally, the destination MAC addresses in Layer 2 protocol packets of the same Layer 2 protocol are the same. For example, the MSTP PDUs are BPDUs with the destination MAC address 0180-C200-0000. Therefore, when a Layer 2 protocol packet reaches an edge device on the ISP network, the edge device cannot identify whether the Layer 2 protocol packet comes from a user network or the ISP network and sends the Layer 2 protocol packets to the CPU to calculate a spanning tree.

In Figure 21-1, devices on user network1 build a spanning tree together with PE1 but not with devices on user network2. As a result, the Layer 2 protocol packets on user network1 cannot traverse the ISP network to reach user network2.

Figure 21-1  Transparent transmission of Layer 2 protocol packets on the ISP network

You can use Layer 2 protocol transparent transmission to transparently transmit Layer 2 protocol packets from the user networks for the ISP network. This addresses the network identity issue. The procedure is as follows:
  1. After receiving Layer 2 protocol packets sent from CE1, PE1 replaces the destination MAC address with a specified multicast MAC address. Then PE1 forwards the packets on the ISP network.
  2. Layer 2 protocol packets are forwarded to PE2. PE2 restores the original destination MAC address of the packets and sends them to CE2.
Huawei device can transparently transmit packets of the following Layer 2 protocols:
  • Spanning Tree Protocol (STP)
  • Link Aggregation Control Protocol (LACP)
  • Ethernet Operation, Administration, and Maintenance 802.3ah (EOAM3ah)
  • Link Layer Discovery Protocol (LLDP)
  • GARP VLAN Registration Protocol (GVRP)
  • GARP Multicast Registration Protocol (GMRP)
  • HUAWEI Group Management Protocol (HGMP)
  • VLAN Trunking Protocol (VTP)
  • Unidirectional Link Detection (UDLD)
  • Port Aggregation Protocol (PAGP)
  • Cisco Discovery Protocol (CDP)
  • Per VLAN Spanning Tree Plus (PVST+)
  • Dynamic Trunking Protocol (DTP)
  • Device Link Detection Protocol (DLDP)
  • Ethernet Synchronization Message Channel (ESMC)
  • User-defined protocols
Updated: 2019-01-18

Document ID: EDOC1100038103

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