Juniper JUNOSE 11.2.X BGP AND MPLS, Руководство по настройке

Страница: 679 / 742

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 on page 642 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 on page 642 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 on page 642 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.
VPWS and BGP/MPLS VPNs Overview
BGP multiprotocol extensions (MP-BGP) enable BGP to support IPv4 services such as
BGP/MPLS VPNs, which are sometimes known as RFC 2547bis VPNs. A VPWS L2VPN
is actually a BGP-MPLS application that has much in common with BGP/MPLS VPNs.
643 Copyright © 2010, Juniper Networks, Inc.
Chapter 14: VPWS Overview