Summary

This chapter introduced basic concepts about broadband subscriber access technologies and services, and the different types of VPN. A VPN can be built in many different ways, using either Layer 2, which you ignore or Layer 3, which you don't ignore core networks. You can build a VPN by overlaying tunnels between customer sites or by using the RFC 2547 model, which usually means that the network uses MPLS. Chapter 2 looks in much more detail at the access technologiesPPP, bridgingincluding how they work, what the encapsulations are, and how you configure them on a Cisco router. Then, Chapter 3 looks at different connectivity scenarios in which it makes sense to use overlay, tunnel-based VPNs.

If you want to know more, the draft-ietf-l3vpn series of documents on http://www.ietf.org are excellent sources of information. For example, draft-ietf-l3vpn-framework-00 has a more rigorous comparison between CPE- and network-based VPN alternatives.

It should be obvious that all these technology choices are for the service provider. The end user really doesn't care if the VPN is made out of tin cans strung together with wires, as long as it gets the job done. To end users, the VPN is about service, with guaranteed levels of performance (price, uptime, latency, and so forth).