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# VPWS Components

Figure 132 shows the components of a typical VPWS L2VPN topology.

Figure 132: VPWS Components

## VPWS Instances

Typically, a VPWS is associated with customers who want to use L2VPNs to connect geographically dispersed sites in their organization across an MPLS-based service provider core, also known as an MPLS backbone. Each VPWS L2VPN consists of the set of provider edge routers running the corresponding VPWS instance. To provide connectivity for the L2VPN, BGP builds pseudowires between the VPWS instances on the provider edge routers participating in a particular VPWS L2VPN point-to-point connection.

Figure 132 depicts two L2VPNs: L2VPN A and L2VPN B. L2VPN A connects Customer A’s Boston and Chicago offices, and consists of provider edge routers PE 1 and PE 2, each of which runs a VPWS instance named l2vpnA. Similarly, L2VPN B 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 VPWS instance named l2vpnB.

## Customer Edge Devices

Figure 132 shows four customer edge devices: CE 1, CE 2, CE 3, and CE 4. Each CE device is located at the edge of a customer site. In the sample topology, CE 1 and CE 3 are members of L2VPN A, and CE 2 and CE 4 are members of L2VPN B.

A CE device can be a single host, a switch, or, most typically, a router. Each CE device is directly connected to an VPWS provider edge router by means of a layer 2 interface.

## VPWS Provider Edge Devices

In a VPWS configuration, E Series routers function as provider edge devices, which are also referred to as PE routers. These PE routers perform a similar function to PE routers in a BGP/MPLS VPN configuration.

Figure 132 depicts 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 an VPWS instance configured for each L2VPN in which it participates. Consequently, the sample topology comprises four separate VPWS instances: instances l2vpnA and l2vpnB configured on PE 1, and instances l2vpnA and l2vpnB configured with matching route target values on PE 2.

Each VPWS instance configured on the router is associated with two types of interfaces. The CE-facing or customer-facing interface is a layer 2 interface that directly connects the PE router to a local CE device. The router encapsulates layer 2 frames from the CE device in an MPLS packet and then forwards the encapsulated frames to the service provider core from an MPLS interface through the provider (P) router. This encapsulation is identical to Martini encapsulation for layer 2 services over MPLS.

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