Hi friend!
Multicast VPN technology allows multicast services to run on BGP/MPLS IP VPN networks. This technology encapsulates multicast packets from a private network to enable the packets to be forwarded along the multicast distribution tree (MDT) on a public network. When the packets reach the destination network, they are decapsulated and forwarded to receivers as multicast packets of the private network.
Multicast VPN is used to address the following problems occurring during the multicast service deployment on BGP/MPLS IP VPN networks:
VPN multicast packets cannot pass the reverse path forwarding (RPF) check on the public network.
In multicast forwarding, multicast routers perform RPF checks on multicast packets based on the multicast source address and inbound interface. Only multicast packets from the RPF interface are forwarded. Each router needs to know the unicast route to the multicast source. The provider (P) device on a BGP/MPLS IP VPN network does not know the VPN routes; therefore, RPF checks fail on the P device.
Overlapping multicast source addresses or group addresses on VPNs lead to inter-VPN communication.
A BGP/MPLS IP VPN network allows overlapping addresses in sites on each VPN; therefore, the multicast source addresses or group addresses of different VPNs may overlap. A PE device must correctly forward multicast packets from a VPN to only the users at the sites on the same VPN to prevent communication between different VPNs.
VPN packets are forwarded in unicast mode on the public network. When the multicast traffic volume is high, loads on the public network increase greatly.
Multicast technology ensures that each link transmits only one copy of multicast packets. Each device replicates multicast data according to the number of outbound interfaces, and the bandwidth consumed does not increase with the number of receivers. If the public network supports multicast forwarding, multicast packets are replicated only at bifurcation points on the public network. This on-demand replication mechanism reduces loads on the public network and conserves bandwidth.
All PE devices on a VPN can receive multicast packets from a multicast source on the same VPN. When the multicast traffic volume is high, loads on the PE devices increase greatly.
A VPN is composed of multiple sites, each of which connects to a different PE. Some sites may not have receivers. If VPN multicast data is forwarded only to the PE devices with receivers connected, burdens on PE devices are reduced.
You can refer to the link https://support.huawei.com/hedex/hdx.do?docid=EDOC1100126530&id=EN-US_TASK_0177091532&lang=en
Hope to help you!
