Vprn Service Overview; Figure 125: Virtual Private Routed Network - Alcatel-Lucent 7750 SR Manual

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VPRN Service Overview

RFC2547bis is an extension to the original RFC 2547, which details a method of distributing

routing information and forwarding data to provide a Layer 3 Virtual Private Network (VPN)

service to end customers.

Each Virtual Private Routed Network (VPRN) consists of a set of customer sites connected to one

or more PE routers. Each associated PE router maintains a separate IP forwarding table for each

VPRN. Additionally, the PE routers exchange the routing information configured or learned from

all customer sites via MP-BGP peering. Each route exchanged via the MP-BGP protocol includes

a Route Distinguisher (RD), which identifies the VPRN association.

The service provider uses BGP to exchange the routes of a particular VPN among the PE routers

that are attached to that VPN. This is done in a way which ensures that routes from different VPNs

remain distinct and separate, even if two VPNs have an overlapping address space. The PE routers

distribute routes from other CE routers in that VPN to the CE routers in a particular VPN. Since

the CE routers do not peer with each other there is no overlay visible to the VPN's routing

When BGP distributes a VPN route, it also distributes an MPLS label for that route. On a SR-

Series, a single label is assigned to all routes in a VPN.

Before a customer data packet travels across the service provider's backbone, it is encapsulated

with the MPLS label that corresponds, in the customer's VPN, to the route which best matches the

packet's destination address. The MPLS packet is further encapsulated with either another MPLS

label or GRE tunnel header, so that it gets tunneled across the backbone to the proper PE router.

Each route exchanged by the MP-BGP protocol includes a route distinguisher (RD), which

identifies the VPRN association. Thus the backbone core routers do not need to know the VPN

displays a VPRN network diagram example.

IP/MPLS Cloud

7750 SR OS Services Guide