Foundations of Layer 3 BGP/MPLS Virtual Private Networks
BGP/MPLS IP VPNs, referred to in short as MPLS L3VPNs or simply L3VPNs throughout this book, are one of the most widely deployed applications enabled by MPLS. When talking about MPLS, it is not fast reroute or traffic engineering that springs to mind, but rather VPN support. In fact, traffic engineering and fast reroute are most often thought about in terms of the benefits that they can provide in the context of a particular service. Perhaps the most popular service is provider-provisioned IP VPNs and the L3VPN solution described in this chapter is the way this service is realized in MPLS networks. For many providers, L3VPNs is the major and sometimes the only driver for deploying MPLS in the network.
VPNs existed long before MPLS. The success of L3 BGP/MPLS VPNs is owed to the scaling and simplicity advantages that the combination of BGP and MPLS brings to VPN scenarios. The L3 BGP/MPLS VPN solution was extended to the Layer 2 space as well, as we will see in the chapters discussing Layer 2 Transport and VPLS (Chapters 12 and 13).
In this chapter we will see how the MPLS VPN solution emerged, introduce its basic principles and concepts and shed light on some of the design decisions taken. We assume the reader has a basic understanding of both MPLS and BGP. In the next chapters we will look at more advanced topics that arise in the context of L3VPNs. Readers familiar with the BGP/MPLS VPN concepts and ...