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:
• Single-Provider Inter-AS—A service provider whose internal network consists of multiple autonomous
systems.
• Intra-Provider Inter-AS—Multiple service providers that need to coordinate their networks to provide
inter-AS support.
To establish a Multicast VPN between two autonomous systems, a MDT-default tunnel must be setup between
the two PE routers. The PE routers accomplish this by joining the configured MDT-default group. This
MDT-default group is configured on the PE router and is unique for each VPN. The PIM sends the join based
on the mode of the groups, which can be PIM SSM, bidir, or sparse mode.
PIM-Bidir is not supported on MVPN.Note
Cisco IOS XR Multicast Configuration Guide for the Cisco CRS Router, Release 5.2.x
21
Implementing Multicast Routing on Cisco IOS XR Software
Multicast VPN
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