Multicast over Layer 3 VPNs Overview

In the unicast environment for Layer 3 VPNs, all VPN state information is contained within the PE routers. However, with multicast for Layer 3 VPNs, Protocol Independent Multicast (PIM) adjacencies are established in one of the following ways:

• You can set PIM adjacencies between the CE router and the PE router through a VRF instance at the [edit routing-instances instance-name protocols pim] hierarchy level. You must include the vpn-group-address statement at this hierarchy level, specifying a multicast group. The rendezvous point (RP) listed within the VRF-instance is the VPN customer RP (C-RP).
• You can also set the master PIM instance and the PE’s IGP neighbors by configuring statements at the [edit protocols pim] hierarchy level. You must add the multicast group specified in the VRF instance to the master PIM instance. The set of master PIM adjacencies throughout the service provider network makes up the forwarding path that becomes an RP tree rooted at the service provider RP (SP-RP). Therefore, P routers within the provider core must maintain multicast state information for the VPNs.

For this to work properly, you need two types of RP routers for each VPN:

• A C-RP—An RP router located somewhere within the VPN (can be either a service provider router or a customer router).
• An SP-RP—An RP router located within the service provider network.

  Note: A PE router can act as the SP-RP and the C-RP. Moving these multicast configuration tasks to service provider routers helps to simplify the multicast Layer 3 VPN configuration process for customers. However, configuration of both SP-RP and VPN C-RP on the same PE router is not supported.

To configure multicast over a Layer 3 VPN, you must install a Tunnel Services Physical Interface Card (PIC) on the following devices:

• P routers acting as RPs
• PE routers configured to run multicast routing
• CE routers acting as designated routers or as VPN-RPs

For more information about running multicast over Layer 3 VPNs, see the following documents:

• Internet draft draft-rosen-vpn-mcast-02.txt, Multicast in MPLS/BGP VPNs
• JUNOS Multicast Protocols Configuration Guide

The sections that follow describe the operation of a multicast VPN. Figure 18 illustrates the network topology used.

Figure 18: Multicast Topology Overview

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