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Which statement is correct in this scenario?

You are establishing RSVP LSPs through your MPLS-enabled network. You are asked to ensure that the LSPs will support end-to-end class-of-service handling.
Which statement is correct in this scenario?

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Configure ultimate-hop-popping on the egress device.

Configure implicit-null on all MPLS-enabled devices.

Configure explicit-null on all MPLS-enabled devices.

Configure entropy-label on the egress device.

2 Comments on “Which statement is correct in this scenario?

  1. Chuck says:

    None of the answers appears good to me. The closest is option A, however ultimate-hop-popping is enabled on the ingress LSPs on the Ingress Router.

    explict-null and ultimate-hop-popping does the same thing in MPLS, they both hand out Label 0, such that the last Service Provider Core router will swap labels instead of popping the label before forwarding the packets to the PE. The PE is where the label is popped and and the packet is forwarded to the appropriate customer.

    While implicit-null hands out Label 3, such that the last router in the Service Provider’s core before the Provider Edge router (where customers are directly connected to) will pop the label and forwards the packet to the PE.


  2. kgdsh says:

    The answer is C: for the reason is that when the explicit-null is used there will not label be pop at the penultimate-hop, instead, a null label will arrive at the target router so that CoS can be handled from the MPLS header ( even though a null label still contains complete info of MPLS header)



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