ZyXEL Communications XGS4700 Series, Manual

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XGS4700-48F 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 142 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
1
2
A
C
Service Provider's
Network
STP
CDP
B
VTP
STP
VTP
CDP