In Layer 3 MPLS VPN implementations, if some of the VPNv4 routes on one PE router do not
appear on another PE router, what could be the problem?

A.
RD mismatch between the PE routers

B.
RT export and import configuration errors

C.
RD export and import configuration errors

D.
VRF name mismatch between the PE routers

Explanation:

http://blog.initialdraft.com/archives/1537/