ZyXEL Communications Plumbing Product metrogigabit switch User Manual

MGS3700-12C User’s Guide

This chapter shows you how to configure layer 2 protocol tunneling on the Switch.

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 150   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.

To emulate a point-to-point topology between two customer switches at different 
sites, such as A and B, you can enable protocol tunneling on edge switches 1 and 

STP

CDP

VTP

STP

VTP

CDP