Click the Exhibit button.
You have an established LSP between your R1 and R5 devices using the configuration shown in the exhibit. You are asked to ensure that MPLS labels are used to forward traffic by all devices within the LSP.
Which action will accomplish this behavior?
To ensure that MPLS labels are used to forward traffic by all devices within the Label Switched Path (LSP), configuring the explicit-null statement under the protocol MPLS hierarchy on R1 is necessary. By default, the penultimate router (the router before the last hop) performs penultimate hop popping (PHP), which removes the MPLS label. Configuring explicit null ensures the penultimate router retains the MPLS label, replacing it with an explicit null label (label value of 0). This way, the egress router knows it has reached the end of the LSP and can perform the appropriate processing.
I think A is the correct Answer
explicit-null applied on egress router under protocol mpls ultimate-hop-popping on ingress router (R1) under lsp configuration
B is corret.
I agree with lukaspi
The question is about penultimate-hop-popping and implicit and explicit null labels.
https://www.juniper.net/documentation/us/en/software/junos/mpls/topics/ref/statement/install-edit-protocols-mpls.html
Correct answer is C
https://www.juniper.net/documentation/us/en/software/junos/mpls/topics/ref/statement/install-edit-protocols-mpls.html