Question

Two service providers operate separate MPLS L3VPN backbones and must interconnect a customer VPN across their ASBRs. The design team chooses Inter-AS Option B (VPNv4 exchange between ASBRs). On the ASBR of AS 100, VPNv4 routes are being received from the peer ASBR in AS 200, but the customer PE devices in AS 100 cannot forward traffic toward the remote prefixes even though the VPNv4 routes appear in BGP. What must be verified on the AS 100 ASBR for Option B to forward customer traffic correctly?

Accepted Answer

That the ASBR rewrites the BGP next hop to itself and allocates a new local MPLS label for each VPNv4 prefix, so a valid label swap exists across the AS boundary

Answer

That the full customer VRF is configured on the ASBR with matching route targets so the routes are imported into a local routing table

Answer

That an LDP session is established directly between the two ASBRs to distribute transport labels across the inter-AS link

Answer

That the ASBR redistributes the received VPNv4 routes into the IGP so the local PEs can learn the remote prefixes