 customer site using conventional IP forwarding. Summary of MPLS VPN MPLS VPN is one of the biggest applications of MPLS used by core network providers. It is an elegant solution to providing a VPN that allows peering between the customer and the provider IP network. One of the most important features of VPN, from the operator's Chapter 13 Multiprotocol Label Switching viewpoint, is that it is a scalable implementation in terms of both configuration management and processor load on the LSRs. The latter is made possible by the fact that the external network address space for each VPN only has to be maintained on each PE router connected to the customer site. No single LSR has to maintain all the routes for all of the VPNs. The key enabling technology for MPLS VPN is the use of BGP at the edge, such that it can maintain routing tables independently for each customer (allowing overlapping address spaces) and can distribute labels to encapsulate traffic for each VPN in its own unique Conclusion MPLS evolved from a methodology to improve switching performance in IP networks, in particular as a replacement for IP over ATM. In practice, the original motivation of forward- ing performance was not the reason for its widespread deployment. Instead, it was the fact that MPLS allows IP control and forwarding functions to be separated that has brought new functionality to IP networks. This chapter has shown how MPLS can provide traffic engi- neering and VPNs in a manner that is difficult to achieve using conventional IP technology. Additionally, MPLS offers significant IP integration that overlay solutions, such as ATM, SONET, and Frame Relay, cannot. It should be noted that MPLS is a complex technology and that only an overview is presented here. Other points of note are that MPLS provides extensive support to a number of higher-layer protocols and many lower-link layer protocols. This has been extended sig- nificantly in generalized MPLS such that MPLS signaling can be used as the control plane for a wide range of circuit-s