STP over Layer 2 MPLS

[ronit]

I am planning to deploy a spanning tree loop between 2 of my Layer 2 MPLS routers and am looking at the "l2protocol forward" combined with "xconnect" to do so. However, I have some questions about how this works

1. So I already have a Layer 2 MPLS Pseudowire between these 2 routers using "l2 vfi" sections and devices can communicate across the pseudowire. Does the pseudowire not forward STP frames by default?

2. When I make the xconnect, how do I know which traffic goes over the xconnect and which traffic goes over the "l2 vfi" pseudowire?

3. What if I make only the xconnect but not the "l2protocol forward"?

4. What if I make only the "l2protocol forward" but not the xconnect?

5. What is the difference between "l2protocol forward", "l2protocol peer" and "l2protocol tunnel" in such a scenario?

Thank you in advance for clarifying my doubts.

[Georg Pauwen]

Hello,

have you actually built this topology already ? Hard to answer your question without having the working topology available. Do you have the configs for all the other devices as well ?

[ronit]

No, this is not built yet, but planned. All the other devices will run mst0, plan old spanning-tree protocol

[Giuseppe Larosa]

Hello @ronit ,

looking at the configurations you have attached to your initial post we see:

l2 vfi TWC-MGMT manual
vpn id 150
bridge-domain 150
neighbor 1.1.1.4 encapsulation mpls
!
!
!
l2 vfi LOCAL-MGMT manual
vpn id 700
bridge-domain 700
neighbor 1.1.1.4 encapsulation mpls
!
!
l2 vfi NET-MGMT manual
vpn id 800
bridge-domain 800
neighbor 1.1.1.4 encapsulation mpls
!
!

You are already defining manually pseudowires at the L2 VFI configuration level, so  I think that you should remove the xconnect command under the interfaces, as they are not needed.

Besides this what kind of STP would you like to carry on pseudowires ?

Are the CE devices running Cisco PVST or Cisco Rapid PVST or standards based 8802.1W  Rapid STP  ( sngle instance) or 802.1S MST ?

Because in Cisco PVST and Rapid PVST BPDUs on trunk interfaces travel tagged with a vlan-id equal to the intenal vlan id value in the BPDU itself  ( this allows for a famous consistency check)

STP is a loop avoidance protocol so you would like to transport STP BDPUs to see if you are able to manage multi homed L2 CE nodes ?

Hope to help

Giuseppe

[ronit]

Giuseppe,

Thank you for your response. 

So do you mean that manual pseudowires will carry all layer 2 frames over it, including STP frames?

The STP I plan to use is plain old mst 0, as these are not Cisco devices.

In actual use, these routers will also have manual pseudowires to other routers for these same BDs, which actually have nothing to do with the STP. How can I make sure the STP BPDUs are forwarded only between these 2 routers, not flooded across all the pseudowires?