Cisco ASR 9000 Series Software Manual page 18

Multicast VPN
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
sent to an MDT tunnel interface are encapsulated, and packets received from a MDT tunnel interface are
decapsulated.
Figure 5: Virtual PIM Peer Connection over an MDT Tunnel Interface
Encapsulating multicast packets in a provider header allows PE routers to be kept unaware of the packets'
origin—all VPN packets passing through the provider network are viewed as native multicast packets and
are routed based on the routing information in the core network. To support MVPN, PE routers only need to
support native multicast routing.
MVPN also supports optimized VPN traffic forwarding for high-bandwidth applications that have sparsely
distributed receivers. A dedicated multicast group can be used to encapsulate packets from a specific source,
and an optimized MDT can be created to send traffic only to PE routers connected to interested receivers.
This is referred to as data MDT.
InterAS Support on Multicast VPN
The Multicast VPN Inter-AS Support feature enables service providers to provide multicast connectivity to
VPN sites that span across multiple autonomous systems. This feature was added to MLDP profile that enables
Multicast Distribution Trees (MDTs), used for Multicast VPNs (MVPNs), to span multiple autonomous
systems.
There are two types of MVPN inter-AS deployment scenarios:
Cisco ASR 9000 Series Aggregation Services Router Multicast Configuration Guide, Release 5.1.x
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Implementing Layer-3 Multicast Routing on Cisco IOS XR Software