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Routing & Switching · Advanced

Inter-AS MPLS VPN

Options for extending MPLS L3VPNs across autonomous systems: Option A (back-to-back VRF), B (VPNv4 eBGP between ASBRs) and C (multihop VPNv4 between RRs).

Definition

Option A treats the other AS as a CE per VRF and is simplest but least scalable. Option B exchanges labeled VPNv4 routes between ASBRs without VRFs. Option C exchanges PE loopbacks with labels (BGP-LU) and VPNv4 via multihop eBGP between route reflectors, the most scalable but requiring trust.

Example

Option B: neighbor 192.0.2.1 remote-as 65002 activated under address-family vpnv4 on the ASBR.

Exam tip

Option A needs a VRF and subinterface per customer on each ASBR.

Related terms