Chapter 27 Layer 2 Protocol Tunneling

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).

Figure 135 L2PT Network Example

 

 

 

 

 

 

 

 

B

A

 

 

 

 

 

 

 

STP

 

 

 

 

 

STP

 

 

 

 

 

 

 

 

 

 

 

STP

 

 

 

D

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Service Provider's

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C

27.1.2.1 Layer 2 Protocol Tunneling Mode

Each port can have two layer 2 protocol tunneling modes, Access and Tunnel.

•The Access port is an ingress port on the service provider's edge device (1 or 2 in Figure 135 on page 252) and connected to a customer switch (A or B). Incoming layer 2 protocol packets received on an access port are encapsulated and forwarded to the tunnel ports.

•The Tunnel port is an egress port at the edge of the service provider's network and connected to another service provider’s switch. Incoming encapsulated layer 2 protocol packets received on a tunnel port are decapsulated and sent to an access port.

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GS2200-24 User’s Guide