BGP MPLS Multicast VPN Overview

BGP MPLS multicast VPNs employ the intra-autonomous system (AS) next-generation (NGEN) BGP control plane and Protocol Independent Multicast (PIM) sparse mode as the data plane.

The main characteristics of multicast VPNs are:

• They extend Layer 3 VPN service (RFC 2547) to support IP multicast for Layer 3 VPN service providers.
• They follow the same architecture as specified by RFC 2547 for unicast VPNs. Specifically, BGP is used as the provider edge (PE) router-to-PE router control plane for multicast VPN.
• They eliminate the requirement for the virtual router (VR) model (as specified in Internet draft draft-rosen-vpn-mcast, Multicast in MPLS/BGP VPNs) for multicast VPNs and the RFC 2547 model for unicast VPNs.
• They rely on RFC 2547-based unicast with extensions for intra-AS and inter-AS communication.

A multicast VPN is defined by two sets of sites, a sender site set and a receiver site set. These sites have the following properties:

• Hosts within the sender site set can originate multicast traffic for receivers in the receiver site set.
• Receivers outside the receiver site set should not be able to receive this traffic.
• Hosts within the receiver site set can receive multicast traffic originated by any host in the sender site set.
• Hosts within the receiver site set should not be able to receive multicast traffic originated by any host that is not in the sender site set.

A site can be in both the sender site set and the receiver site set, so hosts within such a site can both originate and receive multicast traffic. For example, the sender sites set could be the same as the receiver site set, in which case all sites could both originate and receive multicast traffic from one another.

Sites within a given multicast VPN might be within the same organization or in different organizations, which means that a multicast VPN can be either an intranet or an extranet. A given site can be in more than one multicast VPN, so multicast VPNs may overlap. Not all sites of a given multicast VPN have to be connected to the same service provider, meaning that a multicast VPN can span multiple service providers.

Another way to look at a multicast VPN is to say that a multicast VPN is defined by a set of administrative policies. These policies determine both the sender site set and the receiver site set. These policies are established by multicast VPN customers, but implemented by multicast VPN service providers using the existing BGP and MPLS VPN infrastructure.

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