13.16 Chapter Summary

VPNs can be identified in many different ways. This chapter focused mainly on BGP/MPLS VPNs. The discussion covered different VPN models and some of the various topologies that can be used with these models to implement VPN services. Reference was made to the overlay model and the peer-to-peer model. The chapter also examined the operation of full-mesh, partial-mesh , and hub-and-spoke topologies used in VPN implementations .

A major point to understand with VPNs and their implementation is the way that routing information is exchanged, based upon the VPN implementation model. When dealing with the RFC 2547bis implementation, remember that RDs are used to identify each route that should populate each PE router's VRF for a specific VPN. In the peer-to-peer model, this routing information is exchanged between the customer routers and the provider's routers. In the overlay model, the provider provides virtual circuits to the customer routers, and they exchange routing information directly between themselves . This is a new concept of provider-managed versus customer-managed routing, and it is one of the main drivers behind this technology.