Multiple choice technology

In normal operation, what is the job of the penultimate router?

  1. It pops the label and sends the remaining data packet to the egress router.

  2. It pushes an additional label on a packet and sends it to the egress router.

  3. It swaps an incoming label with a label of 3 and sends it to the egress router.

  4. It examines the IP packet and forwards the packet based on the destination IP address.
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A Correct answer
Explanation

The penultimate hop router (second-to-last router in the LSP) performs PHP (Penultimate Hop Popping) by removing the MPLS label before forwarding the packet to the egress router. This reduces processing load on the egress router since it doesn't need to perform a label lookup - it receives a plain IP packet. Option B is incorrect because the penultimate router pops, not pushes. Option C describes a swap operation with explicit null (label 3), not the normal PHP case. Option D is what the egress router does after PHP, not the penultimate router's job.

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