A service provider engineer has been requested to preserve QoS values when customer packets cross the MPLS backbone. Which Cisco IOS command should the engineer apply and what should the label value be when the LSR at the penultimate hop forwards the MPLS label packets toward the egress PE?
A. mpls ldp explicit-null with label value of zero
B. mpls ldp implicit-null with label value of zero
C. mpls ldp explicit-null with label value of three
D. mpls ldp implicit-null with label value of three
