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Question 564

What is the function of penultimate hop popping?

The last P router in the path pops off the transport label before traffic is forwarded toward the PE.

The VPN label is popped off at the egress LSR, and unlabeled traffic is forwarded toward the CE.

The transport label is popped off at the egress LSR, and unlabeled traffic is forwarded toward the CE.

The second to last P router in the path pops off the VPN label before traffic is forwarded to the last P router.

Correct Answer: A

Penultimate hop popping (PHP) is a function in MPLS networks where the last P router, often referred to as the penultimate hop, pops off the transport label before forwarding the traffic to the PE router. This allows the PE router to receive a packet without the MPLS label, avoiding an extra label lookup and simplifying the processing before forwarding the packet to the customer edge (CE) router.

Discussion

vallzoOption: A

A is correct. This way the PE receives a packet without the LDP label, and doesn't have to do an extra lookup in the LFIB before forwarding the packet to a non-MPLS router like CE.

dapardoOption: A

its A: PHP can be performed in frame-based MPLS networks. In these networks, the last P router in the LSP tunnel pops the LDP label as previously requested by the egress PE router through LDP. So, the PE router receives a labeled packet that contains only the VPN label.

d740f62Option: A

Correct