XS1930 Series User’s Guide
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CHAPTER 27
Layer 2 Protocol Tunneling
27.1 Layer 2 Protocol Tunneling Overview
This chapter shows you how to configure layer 2 protocol tunneling on the Switch.
27.1.1 What You Can Do
Use the Layer 2 Protocol Tunnel screen (Section 27.2 on page 215) to enable layer 2 protocol tunneling
on the Switch and specify a MAC address with which the Switch uses to encapsulate the layer 2
protocol packets by replacing the destination MAC address in the packets.
27.1.2 What You Need to Know
Layer 2 protocol tunneling (L2PT) is used on the service provider's edge devices.
L2PT allows edge switches (1 and 2 in the following figure) to tunnel layer 2 STP (Spanning Tree Protocol),
CDP (Cisco Discovery Protocol) and VTP (VLAN Trunking Protocol) packets between customer switches
(A, B and C in the following figure) connected through the service provider’s network. The edge switch
encapsulates layer 2 protocol packets with a specific MAC address before sending them across the
service provider’s network to other edge switches.
Figure 152 Layer 2 Protocol Tunneling Network Scenario
In the following example, if you enable L2PT for STP, you can have switches A, B, C and D in the same
spanning tree, even though switch A is not directly connected to switches B, C and D. Topology change
information can be propagated throughout the service provider’s network.
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