An NG MVPN is a new framework designed to transmit IP multicast traffic across a BGP/MPLS VPN. To exchange control messages and create VPN multicast data channels, each PE on an NG MVPN must be able to discover other PEs on the MVPN. The discovery process is called MVPN membership autodiscovery. An NG MVPN uses BGP to implement this process. To support MVPN membership autodiscovery, BGP defines a new BGP-MVPN address family.
An NG MVPN transmits VPN multicast routes and establishes public network tunnels through control messages defined by BGP-MVPN. BGP-MVPN defines seven types of control messages, which represent seven types of MVPN routes. Type 6 and Type 7 routes are used for VPN multicast joining and VPN multicast traffic forwarding. Type 1-5 routes are used for MVPN membership autodiscovery and P2MP tunnel establishment. Type 6 and Type 7 routes are called C-multicast routes, and Type 1-5 routes are called A-D routes.
NG MVPN routing information is carried in BGP Update messages. Only seven types of control messages are not enough to complete multicast joining/leaving control and P2MP tunnel creation. MVPN extended community and PMSI attributes are introduced for BGP.
After BGP peer relationships are established between PEs in the BGP-MVPN address family, the MVPN extended community attributes control the sending and receiving of C-multicast routes to transmit multicast users' Join/Leave messages. A-D routes help MPLS establish P2MP tunnels. The information used to create a public network tunnel is carried by the PMSI, which is a logical channel used by the public network to carry VPN multicast traffic.