The increasing availability of Ethernet-based multipoint service architectures from service providers, for both L2 VPN and 元 VPN services, is resulting in a growing number of enterprises transitioning their WANs to these multipoint services and VPLS is playing an increasingly important role in this transition.
Therefore in operation, VPLS offers the same connectivity experienced if a device were attached to an Ethernet switch by linking virtual switch instances (VSIs) using MPLS pseudowires to form an "emulated" Ethernet switch.Ĭompared to traditional LAN switching technologies, VPLS is also more flexible in its geographic scaling, so that Customer Edge (CE) sites may be within the same metropolitan domain, or may be geographically dispersed on a regional or national basis. If the destination address is unknown, or is a broadcast or multicast address, the frame is flooded to all ports associated with the virtual bridge. VPLS forwards Ethernet frames at Layer 2, dynamically learns source MAC address to port associations, and forwards frames based upon the destination MAC address. In concept, a VSI is similar to the bridging function found in IEEE 802.1q bridges in that a frame is switched based upon the destination MAC and membership in a Layer 2 VPN (a virtual LAN or VLAN). At a basic level, VPLS can be defined as a group of Virtual Switch Instances (VSIs or VFIs) that are interconnected using EoMPLS circuits in a full mesh topology to form a single, logical bridge, as shown in Figure 3-1. To provide multipoint Ethernet capability, IETF VPLS drafts describe the concept of linking virtual Ethernet bridges using MPLS pseudowires.
The MPLS core uses a full mesh of pseudowires and split-horizon to avoid loops. VPLS is often used by service providers to provide Ethernet Multipoint Services (EMS) and is also being adopted by Enterprises on a self-managed MPLS-based metropolitan area network (MAN) to provide high-speed any-to-any forwarding at Layer 2 without relying on spanning tree to loop free logical topology. Virtual Private LAN Service (VPLS) is an architecture that provides multipoint Ethernet LAN services, often referred to as Transparent LAN Services (TLS) across geographically dispersed locations using MPLS as transport. MC-LAG to VPLS Technology and Solution Overview
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