Configuring MP-EBGP Between AS Border Routers

In this approach, the PE routers within an AS use multiprotocol external BGP (MP-EBGP) to distribute labeled VPN–Internet Protocol version 4 (IPv4) routes to an AS border router or to a route reflector of which the AS border router is a client. The AS border router uses multiprotocol external BGP (MP-EBGP) to distribute the labeled VPN-IPv4 routes to its peer AS border router in the neighboring AS. The peer AS border router then uses MP-IBGP to distribute labeled VPN-IPv4 routes to PE routers, or to a route reflector of which the PE routers are a client.

This approach enhances the scalability of an EBGP VRF-to-VRF configuration because it eliminates the need to configure all the VPNs on every AS border router. However, it also introduces some complexity:

• All the VRF routes must be stored in the AS border router.
• An LSP must be established from ingress PE routers to egress PE routers.
• Secure connections must exist among the ASs along the path from the ingress PE router to the egress PE router.
• The ASs must be configured to store information about which AS border routers receive routes with specific route target attributes.

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