What does penultimate hop popping (PHP) perform?

Penultimate Hop Popping (PHP) is a feature of MPLS that optimizes label switching. When PHP is enabled, the Label Switching Router (LSR) that is one hop away from the egress LSR (the "penultimate" hop) removes the transport label from the packet. This means the egress LSR receives an IP packet, not a labeled MPLS packet. This reduces the processing overhead on the egress LSR, as it doesn't need to perform a label lookup and pop operation. In the context of MPLS VPNs, the "last P router" (Provider router) is the penultimate hop to the egress PE (Provider Edge) router. It pops the transport label, and the PE then receives the packet with only the VPN label (or no label if it's the final destination). Incorrect options: The VPN label is popped off at the egress LSR, and unlabeled traffic is forwarded toward the CE: This describes the egress PE's role in removing the VPN label, not PHP. The transport label is popped off at the egress LSR, and unlabeled traffic is forwarded toward the CE: This is standard MPLS behavior without PHP for the transport label. PHP specifically moves this operation to the penultimate hop. The second to last P router in the path pops off the VPN label before traffic is forwarded to the last P router: PHP applies to the transport label, not the VPN label, and the VPN label is typically popped at the egress PE.