Ensure Full Label Stack with Hop-by-Hop and VPN Labels in RSVP for MPLS LSPs
Question
You are using RSVP in your network to signal MPLS LSPs. You are asked to ensure that the egress MPLS router receives the full label stack, containing both the hop-by-hop and VPN label.
Answers
Explanations
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A. B. C. D.A
The correct answer to the question is B. Use the set protocols mpls expand-loose-hop command.
When using MPLS with RSVP-TE signaling, it is possible to have multiple label stacks in a single LSP. In a typical MPLS network, the ingress router assigns labels to packets based on the forwarding equivalence class (FEC) of the destination address. These labels are then propagated through the network using label distribution protocols such as LDP or RSVP-TE.
RSVP-TE is a protocol that allows for the establishment of LSPs with explicit routes and resource reservations. RSVP-TE signaling can carry multiple label stacks, which may include both hop-by-hop labels and VPN labels. The hop-by-hop labels are used for forwarding packets through the core of the network, while the VPN labels are used for delivering packets to specific VPNs.
In order to ensure that the egress MPLS router receives the full label stack, containing both the hop-by-hop and VPN label, we need to use the set protocols mpls expand-loose-hop command. This command enables the router to expand the loose hop in the RSVP-TE signaling message, allowing the full label stack to be propagated to the egress router.
The other options listed are not relevant to this particular problem. The set protocols mpls explicit-null command is used to specify that the label stack should be terminated with an explicit null label. This can be useful in some cases, but it does not help in ensuring that the egress router receives the full label stack.
The set protocols rsvp keep-multiplier command is used to configure the RSVP-TE hello interval and the multiplier used to calculate the timeout interval for RSVP-TE messages. This is not relevant to the problem of ensuring that the egress router receives the full label stack.
The set protocols rsvp interface <interface> no-aggregate command is used to disable the aggregation of RSVP-TE messages on the specified interface. This can be useful in some cases, but it does not help in ensuring that the egress router receives the full label stack.
