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Multicast VPN
so that the PIM protocol is enabled in the provider core, and mrib/mfib is used for forwarding p-packets
in the core.
• MLDP ones (Rosen, partition): MVPN allows a service provider to configure and support multicast
traffic in an MPLS VPN environment. This type supports routing and forwarding of multicast packets
for each individual VPN routing and forwarding (VRF) instance, and it also provides a mechanism to
transport VPN multicast packets across the service provider backbone. In the MLDP case, the regular
label switch path forwarding is used, so core does not need to run PIM protocol. In this scenario, the
c-packets are encapsulated in the MPLS labels and forwarding is based on the MPLS Label Switched
Paths (LSPs) ,similar to the unicast case.
In both the above types, the MVPN service allows you to build a Protocol Independent Multicast (PIM) domain
that has sources and receivers located in different sites.
To provide Layer 3 multicast services to customers with multiple distributed sites, service providers look for
a secure and scalable mechanism to transmit customer multicast traffic across the provider network. Multicast
VPN (MVPN) provides such services over a shared service provider backbone, using native multicast
technology similar to BGP/MPLS VPN.
MVPN emulates MPLS VPN technology in its adoption of the multicast domain (MD) concept, in which
provider edge (PE) routers establish virtual PIM neighbor connections with other PE routers that are connected
to the same customer VPN. These PE routers thereby form a secure, virtual multicast domain over the provider
network. Multicast traffic is then transmitted across the core network from one site to another, as if the traffic
were going through a dedicated provider network.
Multi-instance BGP is supported on multicast and MVPN. Multicast-related SAFIs can be configured on
multiple BGP instances.
Multicast VPN Routing and Forwarding
Dedicated multicast routing and forwarding tables are created for each VPN to separate traffic in one VPN
from traffic in another.
The VPN-specific multicast routing and forwarding database is referred to as MVRF. On a PE router, an
MVRF is created when multicast is enabled for a VRF. Protocol Independent Multicast (PIM), and Internet
Group Management Protocol (IGMP) protocols run in the context of MVRF, and all routes created by an
MVRF protocol instance are associated with the corresponding MVRF. In addition to VRFs, which hold
VPN-specific protocol states, a PE router always has a global VRF instance, containing all routing and
forwarding information for the provider network.
Multicast Distribution Tree Tunnels
The multicast distribution tree (MDT) can span multiple customer sites through provider networks, allowing
traffic to flow from one source to multiple receivers. For MLDP, the MDT tunnel trees are called as Labeled
MDT (LMDT).
Secure data transmission of multicast packets sent from the customer edge (CE) router at the ingress PE router
is achieved by encapsulating the packets in a provider header and transmitting the packets across the core. At
the egress PE router, the encapsulated packets are decapsulated and then sent to the CE receiving routers.
Multicast distribution tree (MDT) tunnels are point-to-multipoint. A MDT tunnel interface is an interface that
MVRF uses to access the multicast domain. It can be deemed as a passage that connects an MVRF and the
global MVRF. Packets sent to an MDT tunnel interface are received by multiple receiving routers. Packets
Cisco IOS XR Multicast Configuration Guide for the Cisco CRS Router, Release 5.2.x
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Implementing Multicast Routing on Cisco IOS XR Software
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