Standard VPNs

The traditional distinction between internal routes and external routes also applies to VPN routing architectures. As shown in Routers in a VPN, the provider (P) routers maintain only the service provider’s internal routes (to provider edge [PE] routers and other P routers); they do not maintain VPN routes. PE routers are the only devices in the provider network that are required to maintain external routes.

The BGP next hop connects the external routes to the internal routes in traditional VPNs:

• The BGP next hop is advertised with each external route in BGP advertisements.
• The route to the BGP next hop is an internal route that is advertised by the IGP.
• MPLS provides packet forwarding from the ingress PE router to the BGP next-hop egress PE router.