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Author(s) Olivier Bonaventure
Deadline Geen deadline
Submission limit No limitation

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Stacked LSPs

In some MPLS networks, large LSPs carry smaller LSPs. This improves the scalability of the network by reducing the number of LSPs that need to be handled by the core LSRs.

Consider the network below where the large LSP (shown with a magenta line) carries three small LSPs (shown with dotted red, blue and green lines).

https://inginious.info.ucl.ac.be/course/lingi2142-QCM/mpls-large-lsp/mpls-large-lsp.png

Here is the LFIB of LSR R2

Label Nexthop Operation
L7 RX POP
L8 RY POP
L2 RZ POP

Here is the LFIB of LSR R3

Label Nexthop Operation
L5 R2 SWAP(L8)
L2 R2 SWAP(L7)
L7 R2 SWAP(L2)

Here is the LFIB of LSR R1

Label Nexthop Operation
L5 R3 POP

Here is the LFIB of LSR R6

Label Nexthop Operation
L9 R1 SWAP(L5)

Here is the LFIB of LSR R7

Label Nexthop Operation
L9 R6 SWAP(L5);PUSH(L9)
L8 R6 SWAP(L2);PUSH(L9)
L7 R6 SWAP(L7);PUSH(L9)

Here is the LFIB of LSR R8

Label Nexthop Operation
L11 R7 SWAP(L9)
L3 R7 SWAP(L7)
L8 R7 SWAP(L8)

Question 1: Label to reach px

What is the label that router R4 needs to use to reach px ?

Question 2: Label to reach py

What is the label that router R4 needs to use to reach py ?

Question 3: Label to reach pz

What is the label that router R4 needs to use to reach px ?