Refer to the diagram.
Which statement is true about packet forwarding across an MPLS VPN backbone?
A.
Penultimate hop popping (PHP) on the LDP label is performed by the egress PE router.
B.
Penultimate hop popping (PHP) on the VPN label is performed by the second P router.
C.
Penultimate hop popping (PHP) on the VPN label is performed to egress PE router.
D.
Penultimate hop popping (PHP) on the LDP label is performed by the second P router.
Explanation:
Penultimate hop popping, or PHP (the removal of the top label in the stack on the hop prior to the
egress
router), can be performed in frame-based MPLS networks. In these networks, the last P router in
the label
switched path (LSP) tunnel pops the LDKP label (as previously requested by the egress PE router
through LDP), and the PE router receives a labeled packet that contains only the VPN label. In
most cases, a single label lookup performed on that packet in the egress PE router is enough to
forward the packet toward the CE router. The full IP lookup through the Forwarding information
Base (FIB) is performed only once, in the ingress PE router, even without PHP. Reference: Cisco
Press – “Implementing Cisco MPLS study guide” p.4-99