Layer 2 Protocol Tunneling; Layer 2 Protocol Tunneling Overview - ZyXEL Communications GS3700 Series User Manual

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Layer 2 Protocol Tunneling

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

27.1 Layer 2 Protocol Tunneling Overview

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 157 Layer-2 Protocol Tunneling Network Scenario
A C
Service Provider's
STP
Network
STP
CDP
1
2
CDP
VTP
VTP
B
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 2 for PAgP (Port Aggregation
Protocol), LACP or UDLD (UniDirectional Link Detection).
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