Multicast over Layer 3 VPNs Overview
In the unicast environment of a Layer 3 VPN, all VPN state information is contained within the PE routers. In a multicast Layer 3 VPN environment, Protocol Independent Multicast (PIM) adjacencies are established between the CE router and the PE router and between the master PIM instance. They are configured at the [protocols pim] hierarchy level on the IGP neighbors of the PE router. The set of master PIM adjacencies on the service provider's network make up the forwarding path, which consists of a rendezvous point (RP) tree rooted at the RP within the service provider's network.
Therefore, provider (P) routers within the provider network must maintain multicast state information for the Layer 3 VPNs. For this to function, there must be two types of rendezvous points for each VPN:
- The VPN-RP, an RP that resides within the VPN
- The service provider RP (SP-RP), which resides within the service provider network
A PE router can act as an SP-RP, but cannot be the VPN-RP of a Layer 3 VPN. The VPN-RP must be located on a CE router or some other customer router within the VPN.
To configure multicast over a Layer 3 VPN, you must install a Tunnel Services Physical Interface Card (PIC) on the following devices:
- Provider routers acting as rendezvous points
- PE routers configured to run multicast routing
- CE routers acting as destination routers or as VPN-RPs
For more information about running multicast over Layer 3 VPNs, see the following documents:
- Multicast in MPLS/BGP VPNs, Internet draft draft-rosen-vpn-mcast-02.txt
- JUNOS Internet Software Configuration Guide: Multicast
The sections that follow describe the operation of a multicast VPN. Figure 14 illustrates the network topology used.
