MPLS’s Newest Application: Layer-2 VPNs
by Mary Petrosky

Published February 2002




At its inception in the mid-1990s, Multiprotocol Label Switching (MPLS) emerged as a fast-packet forwarding scheme to improve router performance. But when the advent of hardware-based routing eclipsed this use, the industry's focus shifted to applying MPLS's connection-oriented characteristics to traffic engineering in large networks. More recently, MPLS has been used for creating Layer-3 (IP-based) virtual private networks (VPNs), based on techniques defined by the IETF in RFC 2547, RFC 2764 and other documents.


Now, another application for the technology has emerged—Layer 2 VPNs. Spurred by interest among service providers, IETF specifications are being defined that spell out how Layer 2 traffic, such as Ethernet, frame relay and ATM traffic, can be transported across an MPLS network. This will allow service providers to accommodate legacy customer traffic—especially lucrative frame relay services—while moving to next-generation IP-oriented network architectures.


The technology also may appeal to IT managers in large enterprises that are used to running their own metro and wide-area networks. For small and medium-size businesses, network managers could see more service options, including emulated LAN services, as well as higher-speed connections for existing Layer 2 services.


Although no standards have yet been nailed down, several equipment makers have already announced support for the IETF Martini drafts, with more vendor implementations in the works. Bearing the name of Level 3's senior architect, Luca Martini, the Martini drafts define encapsulation and label-distribution mechanisms for transporting frame relay, ATM, Ethernet, High-level Data Link Control (HDLC) and Point-to-Point Protocol (PPP) traffic across an MPLS network.


While the emphasis in recent years has been on IP and IP-related services, the fact remains that many service providers derive a significant portion of their revenue from data and voice services based on legacy technologies such as frame relay, ATM, and time division multiplexing (TDM). Greenfield and established service providers alike want to make money from these traditional services even as they build out their IP infrastructures. Service providers such as Level 3 and Cable & Wireless see MPLS-based L2 VPNs as key to their ability to consolidate their network architectures around IP and MPLS while supporting existing customer frame relay and ATM traffic and potentially expanding into Ethernet transport.


Clearly, development of MPLS L2 VPN standards is in the early stages. Early adopters of Martini-based solutions face the classic problems all early adopters face, including a lack of solid provisioning and management tools. However, momentum is building for MPLS L2 VPNs built around the Martini approach, because the solution addresses real service provider and enterprise customer requirements. Regardless of how widely it's ultimately deployed, the Martini approach has already found a market.



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