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MPLS-TP P-Router Label Swap


In an MPLS LSP, my understanding is that the PE router will put dual lable.

1) The outer LABEL is for LSP and inner Label is for curresponding Pesudowire (PW)

2) once the packet exits from the NNI interface of PE it will might reach to neighbor P-router

what is the action taken by P-router, will it just switch since ther is no control plane or it will 'swap' the lable of LSP (PW lable unchanged) and forward to next hop ??

My doubt is on the Label swapping feature ?

Once answered I will ask other question on PW OAM. ..


Prasad K

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Cisco Employee

MPLS-TP P-Router Label Swap


I am not that familiar with MPLS-TP but I suppose that even with MPLS-TP, a basic MPLS LSP uses just a single label. You would need to construct a pseudowire in order to have a stack of two labels.

Once a P-router receives a labeled packet, it does not care how many labels are in the stack. All it cares about is whether it knows what to do with the topmost label, and the usual operation would be a SWAP operation. The lack of control plane has nothing to do with this: if the LSP has been established on its entire span then the central control element must have ensured that all routers along the LSP's path have proper label swap/pop information.

Please note there is no option of "just switching the labeled packet".

Best regards,