Multicast virtual private network (VPN) technology allows multicast services to run on Border Gateway Protocol or Multiprotocol Label Switching (BGP/MPLS) IP VPN networks.
Multicast VPN technology encapsulates multicast packets from privates network so that they can be forwarded along a multicast distribution tree (MDT) on a public network. When these packets reach their destination network, they are decapsulated and forwarded to receivers as private network multicast packets.
Multicast VPN addresses the following problems that occur during multicast service deployment on BGP/MPLS IP VPN networks:
VPN multicast packets are unable to pass reverse path forwarding (RPF) checks on a public network.
Multicast forwarding requires routers to 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 must have a unicast route to the multicast source within its routing table. Provider (P) devices on a BGP/MPLS IP VPN network do not have VPN routes, so multicast packets cannot pass RPF checks the P devices.
Inter-VPN communication is caused by overlapping multicast source addresses or group addresses.
BGP/MPLS IP VPN networks allow different VPNs to have overlapping multicast source addresses or group addresses. Provider edge (PE) routers must prevent communication between different VPNs by forwarding VPN multicast packets only within the correct VPN.
If VPN packets are forwarded in unicast mode on the public network, load on the public network will increase greatly when the multicast traffic volume is high.
Multicast technology ensures that each link transmits only one copy of multicast packets. Each router replicates multicast data according to the number of outbound interfaces, so the bandwidth consumption does not increase with the number of receivers. If the public network supports multicast forwarding, multicast packets are replicated only at dividing points. This on-demand replication mechanism reduces public network load and conserves bandwidth.
PE routers can receive multicast packets from a multicast source within the same VPN. Load on PE routers increases greatly when the multicast traffic volume is high.
A VPN is composed of multiple sites, each of which connects to a different PE router. Not all sites have receivers. Forwarding VPN multicast data to only PE routers with receivers connected can reduce load on PE routers.
To carriers, multicast VPN technology allows them to provide multicast services to VPN users. The public network does not need to know multicast data sent to VPN users, whereas VPNs do not need to have multicast routing information on the public network.
To enterprises, multicast VPN technology allows them to deploy their own multicast services on VPNs provided by carriers. Multicast services of enterprises on different VPNs are isolated.