Draft-Rosen Multicast VPNs Overview

The Junos OS provides three ways to configure IP version 4 (IPv4) multicast over Layer 3 VPNs:

• Draft-rosen multicast VPNs—Described in RFC 4364, BGP/MPLS IP Virtual Private Networks (VPNs) and based on the IETF Internet draft draft-rosen-vpn-mcast-07.txt, Multicast in MPLS/BGP IP VPNs. Draft-rosen multicast VPNs can be configured with service provider tunnels operating in any-source multicast (ASM) mode or source-specific multicast (SSM) mode. For more information about these types of draft-rosen multicast VPNs, see the Junos Multicast over Layer 3 VPNs Feature Guide.
• Draft-rosen multicast VPNs—Described in RFC 4364, BGP/MPLS IP Virtual Private Networks (VPNs) and based on Section Two of the IETF Internet draft draft-rosen-vpn-mcast-06.txt, Multicast in MPLS/BGP VPNs (expires April 2004).
• Multiprotocol BGP-based multicast VPNs (also referred to as next-generation Layer 3 VPN multicast)—Defined by a set of sender sites and a set of receiver sites, they use BGP as the signaling protocol.

Note: Draft-rosen multicast VPNs are not supported in a logical system environment even though the configuration statements can be configured under the logical-systems hierarchy.

Draft-rosen multicast VPNs (MVPNs) with service provider tunnels operating in SSM mode do not require that the provider (P) routers maintain any VPN-specific PIM information.

Draft-rosen MVPNs with service provider tunnels operating in SSM mode make use of two types of multicast distribution trees (MDTs); a default MDT and one or more data MDTs.

Draft-rosen MVPNs with service provider tunnels operating in SSM mode start by sending all multicast traffic over a default MDT, as described in section 7 of Internet draft draft-rosen-vpn-mcast-07.txt. This default mapping results in the delivery of packets to each provider edge (PE) router attached to the provider router even if the PE router has no receivers for the multicast group in that VPN. Each PE router processes the encapsulated VPN traffic even if the multicast packets are then discarded.

A data MDT, as described in Data MDTs Overview, solves the problem of routers flooding unnecessary multicast information to PE routers that have no interested receivers for a particular VPN multicast group.

The default MDT uses multicast tunnel (mt-) logical interfaces. Data MDTs also use mt logical interfaces. If you administratively disable the physical interface that the mt logical interfaces are configured on, the mt logical interfaces are moved to a different physical interface that is up. In this case the traffic is sent over the default MDT until new data MDTs are created as described in Data MDT Characteristics.