单项选择题
A. CEF switching is only needed to forward labeled packets.
B. CEF switching is needed on both ingress and egress interfaces on which MPLS is enabled.
C. Interface-level CEF switching is needed only on egress interfaces that are sending IP packets on which the egress LSR performs the label imposition process.
D. Interface-level CEF switching is needed only on ingress interfaces that are receiving IP packets on which the ingress LSR performs the label imposition process.