L2TPv3 (Layer 2 Tunnel Protocol Version 3)

[lagapidis (Lazarus Agapidis)]

Hello Sean

To achieve what you’re trying to do, you need something like this:

R1 and R2 are the devices that support L2TPv3. By configuring pseudowire on the Gi0/0 interfaces of R1 and R2, you are creating a Layer 2 tunnel between the two Gi0/0 interfaces on the routers, that is being tunneled through the Layer 3 underlay. The result is as if you are connecting two layer 2 ports of SW1 and SW2 directly.

The reason why you have to configure it on physical ports is that the pseudowire feature and the xconnect command can only be applied to physical Layer 3 interfaces. The mechanism of encapsulation actually takes place at the physical Gi0/0 interfaces of the routers.

You can configure the connecting ports of SW1 and SW2 as access ports or trunk ports. You can then span as many VLANs as you want across the Layer 3 infrastructure. They’ll function as if you have connected the switches directly to one another. Does that make sense?

I hope this has been helpful!

Laz

[lagapidis (Lazarus Agapidis)]

Hello Sean

@sean.solina

will BPDUs also traverse the tunnel?

Yes, BPDUs will also traverse the tunnel. Once again, using anTPv3 tunnel is just like connecting two switches using a Layer 2 link.

@sean.solina

So if there is a network loop on the far side of the tunnel, will that also send STP packets to cause a root recalculation and bring down the network?

The connected switches will participate in STP, and will be affectθed by any loops that are detected. But keep in mind that unless the devices on either end of the L2TPv3 tunnel are connected by some other Layer 2 connection, you will never have a loop, and the L2TPv3 tunnel will never be blocked by STP. Only if you have two or more Layer 2 connections between the devices connected over that L2TPv3 link could you have such a scenario. Does that make sense?

I hope this has been helpful!

Laz