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# VPLS Components

As illustrated in Figure 127, a typical VPLS topology consists of the following components.

## VPLS Domains

Typically, a VPLS domain is associated with customers who want to use Ethernet-based layer 2 VPNs to connect geographically dispersed sites in their organization across an MPLS-based service provider core, also known as an MPLS backbone. Each VPLS domain consists of the set of PE routers running the corresponding VPLS instance that participates in that domain. In BGP-signaled VPLS, a VPLS domain is identified by the route target extended community, similarly to how a layer3 VPN domain is identified in layer 3VPNs.

Figure 127depicts two VPLS domains: VPLS A and VPLS B. The VPLS A domain connects Customer A’s Boston and Chicago offices, and consists of provider edge routers PE 1 and PE 2, each of which runs a VPLS instance named vplsA. Similarly, the VPLS B domain connects Customer B’s Boston and Chicago offices, and consists of provider edge routers PE 1 and PE 2, each of which also runs a VPLS instance named vplsB.

## Customer Edge Devices

Figure 127 shows four customer edge (CE) devices: CE 1, CE 2, CE 3, and CE 4. Each CE device is located at the edge of a customer site, and participates in one or more VPLS domains. In the sample topology, CE 1 and CE 3 are members of the VPLS A domain, and CE 2 and CE 4 are members of the VPLS B domain.

A CE device can be a single host, a switch, or, most typically, a router. Each CE device is directly connected to a VPLS edge router by means of an Ethernet or bridged Ethernet network interface, but does not run VPLS. From the perspective of the CE device, the entire VPLS network appears to be a single layer 2 switch that can switch layer 2 packets, learn and filter on media access control (MAC) addresses, and flood packets that have unknown MAC destination addresses (DAs).

## VPLS Edge Devices

In a VPLS configuration, E-series PE routers host VPLS edge (VE) devices, which are also referred to as VE routers or, simply, VEs. A VE device is a VPLS instance that services a particular customer site.

Figure 127depicts two PE routers: PE 1, which is the local router, and PE 2, which is the remote router located at the other side of the service provider core. Each PE router must have a VPLS instance—the VE device—configured for each VPLS domain in which it participates. Consequently, the sample topology comprises a total of four separate VPLS instances: instances vplsA and vplsB configured on PE 1, and instances vplsA and vplsB configured with matching route target values on PE 2.

Each VPLS instance configured on the router is associated with two types of interfaces, also known as ports. The CE-facing interface is an Ethernet or bridged Ethernet network interface that directly connects the PE router to each CE device. The VPLS virtual core interface, although not an actual physical interface, is automatically generated by the router for each VPLS instance and represents all of the MPLS tunnels from the router to the remote PE devices. The router encapsulates Ethernet frames from the CE device in an MPLS packet and then forwards the encapsulated frames to the service provider core through the provider (P) router. This encapsulation is identical to Martini encapsulation for Ethernet layer 2 services over MPLS.

Each PE router in the sample topology has a total of two network interfaces and two VPLS virtual core interfaces configured, one interface of each type per VPLS instance.

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