Sunday, October 10, 2010

Multicast for MPLS VPN

We need to transport multicast traffic across our enterprise MPLS core network for users to receive their favorite Channel News Asia and CNN live broadcasts on their workstations. I found this updated Cisco resource - Configuring Multicast VPN (MVPN) - for IOS 12.4, which is different from the older IOS versions. The newer version support MDT SAFI, which will be automatically created when the default MDT (Multicast Distribution Tree) exists. The default MDT defines the path used by PE routers to send multicast data and control messages to every other PE router in the multicast domain. The setting up of MDT involves the following steps:

  1. Configuring a Default MDT Group for a VRF (required)

  2. Configuring the MDT Address Family in BGP for Multicast VPN (required)

  3. Configuring the Data Multicast Group (optional)

Data MDTs, which are dynamically created, are intended for high-bandwidth sources such as full-motion video inside the VPN to ensure optimal traffic forwarding in the MPLS VPN core. When the multicast transmission exceeds the defined threshold, the sending PE router creates the data MDT and sends a UDP message, which contains information about the data MDT to all routers on the default MDT. The threshold at which the data MDT is created can be configured on a per-router or a per-VRF basis. However, Data MDTs are created only for shared tree (S, G) multicast route entries within the VRF multicast routing table. They are not created for source tree (*, G) entries regardless of the value of the individual source data rate.