In MPLS VPN implementations, how are the second (VPN) labels in the label stack propagated
from the
egress PE router to the ingress PE router?

A.
The core IGP.

B.
MP-IBGP VPNv4 routing updates.

C.
MP-IBGP IPv4 routing updates.

D.
EBGP IPv4 routing ipdates

E.
LDP

F.
TDP