ZyXEL Communications MES3500-24, User Manual

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MES3500-24/24F User’s Guide
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Layer 2 Protocol Tunneling
This chapter shows you how to configure layer-2 protocol tunneling on the Switch.
29.1 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 132
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.
1
2
A C
Service Provider's
Network
STP
CDP
B
VTP
STP
VTP
CDP