L2PT Configuration

L2PT (Layer 2 Protocol Transparent Transmission) is a technology used to extend Local Area Network (LAN) connections across Wide Area Networks (WAN). Simply put, it allows Layer 2 protocol packets from user networks in different geographical locations (such as corporate headquarters and branch offices) to be transparently transmitted through the carrier network (or large enterprise backbone network) as if passing through a “dedicated tunnel.

Explanation of Principles

• On the user access side of the backbone network, the multicast destination MAC address of the original Layer 2 protocol packet is replaced with a specific multicast MAC address.
• After the MAC address is modified, the packet traverses the backbone network. Depending on the configured transparent transmission mode, the network decides whether to process the packet or not.
• When the Layer 2 protocol packet reaches the egress node, the device matches the packet against the configured mapping relationship between the special multicast destination MAC addresses and the Layer 2 protocols. It then restores the packet’s multicast destination MAC address to the standard one defined for that specific Layer 2 protocol. Finally, based on the configured transparent transmission mode, it decides whether to process the packet.

L2PT Configuration

Configure Tasks	Instructions
Enter the interface configuration view	interface ethernet* id*
Configure the protocol packet to be discarded	l2protocol-packet {stp|lacp} disable
Enable L2PT	l2protocol-tunnel {stp|lacp|cdp|pvstp} enable

Configuration Example

The CE devices are the edge devices of the enterprise located in different geographical networks, while PE1 and PE2 are the edge devices of the carrier network. The two enterprise networks are Layer 2 networks and are interconnected through the carrier network. To prevent loops in the Layer 2 network, the Spanning Tree Protocol (STP) is enabled, and the enterprise requires STP to run only within its own networks to form a correct spanning tree.

Procedure

1. The configuration of CE1 and CE2 is the same, here is the example of CE1
2. Create VLAN 100, 200 and add the corresponding physical interfaces to the VLAN

sonic(config)# vlan 100
sonic(config)# interface ethernet 2
sonic(config-if-2)# switchport trunk vlan 100
sonic(config-if-2)# exit
sonic(config)# stp mode stp
sonic(config)# mstp enable

3. Add Ethernet3 interfaces of PE1 and PE2 to VLAN 100, and enable Layer 2 protocol tunneling on the PE devices

sonic(config)# interface ethernet 3
sonic(config-if-3)# l2protocol-packet stp disable
sonic(config-if-3)# l2protocol-tunnel stp enable

4. Verify configuration

sonic# show stp status
Spanning-tree Mode: stp
vlan      mst instance  port_role_state
------  --------------  --------------------------------------------
Vlan100              0  Ethernet2(Root)(forw)