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MPLS Layer 3 VPN Migrations
If MPLS has revolutionized the internetworking industry over the last ten years, BGP-based Layer 3 VPNs (L3 VPNs) are probably their most popular and widespread application. In fact, the ability to construct virtual and independent Layer 3 topologies over the same network in a scalable and flexible fashion and based simply on routing paradigms has been a major factor and business driver for many service providers and enterprise networks just to start implementing MPLS.
A common exercise over the last several years at many internetworks has been a migration from a traditional flat topology to a VPN-structured MPLS environment, not only to offer additional services but also as a security mechanism or for the sake of controlled and isolated management at each L3 VPN.
MPLS BGP-based L3VPNs have gained so much popularity that different interconnect models have been precluded and evolved over time. These inter-AS interconnect types have allowed flexible disposition of Layer 3 VPNs across different backbones and providers with more granular or scalable approaches to stitch them.
[RFC2547] (now evolved to [RFC4364]) started as an appeal to the concept of defining MPLS-based L3VPNs to support the outsourcing of IP backbone services for enterprise networks. The idea was to benefit from MPLS features to deploy independent VPNs over the same global architecture and to have the features be completely separate without a need for specific security constructs.
