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MX Series Router Cloud CPE Draft-Rosen Multicast VPN Services Overview

Junos OS supports Layer 3 VPNs based on the Internet draft draft-rosen-rfc2547bis, BGP/MPLS VPNs. This Internet draft defines a mechanism by which service providers can use their IP backbones to provide Layer 3 VPN services to their customers. The sites that encompass a Layer 3 VPN are connected over the provider’s existing public Internet backbone.

In a unicast environment for Layer 3 VPNs, all VPN states are contained within the PE routers. With multicast over Layer 3 VPNs, two PIM adjacencies are established: One between the CE router and the PE router through a VRF routing instance, the second between the main PE routers and their service provider core neighbors. The set of master PIM adjacencies throughout the service provider’s network provides the forwarding paths, and eventually forms a rendezvous point (RP) multicast distribution tree. The tree is rooted at the RP contained within the service provider’s network. As a result, core provider transit routers within the service provider’s network must maintain multicast state information for the VPNs.

For draft-rosen multicast virtual private networks (MVPNs) to work correctly, there must be two types of rendezvous points. The VPN customer rendezvous point (VPN C-RP) is an RP that resides within a VPN, which connects the segments of a customer network. The service provider rendezvous point (SP-RP) resides within the service provider network itself. Because a PE router connects to both the customer network and the service provider network, the PE router acts as an SP-RP, a VPN C-RP, or both.

In MVPNs, the Layer 3 CPE must run the PIM protocol to form the multicast distribution tree in the customer network. Typically, C-RP is running in the Layer 3 CPE. Optionally, you can enable the bootstrap router (BSR), or auto-RP, to support C-RP redundancy. Moving to the cCPE architecture, the Layer 3 CPE is replaced with a Layer 2 CPE. IP multicast traffic can pass through the Layer 2 CPE, which replicates the multicast packets to all interfaces if IGMP snooping is not enabled. C-RP and BSR, or auto-RP functions, are moved to the cCPE architecture (the VRF routing instance in the adjacent PE router). The MX Series router supports C-RP, BSR, and auto-RP in VRF routing instances. If there is more than one Layer 2 interface in the cCPE bridge domain, IGMP snooping can be enabled in the bridge domain to ensure that IP multicast packets are replicated only to interfaces with receivers.