1282 CHAPTER 75: M ULTICAST VPN C ONFIGURATIONIntroduction to MD-VPNn For details about the concepts of Protocol Independent Multicast (PIM), bootstraprouter (BSR), candidate-BSR (C-BSR), rendezvous point (RP), candidate RP (C-RP),shortest path tree (SPT) and rendezvous point tree (RPT), refer to “PIMConfiguration” on page 1161.Router implements multicast VPN by means of the multicast domain (MD)method. This multicast VPN implementation is referred to as MD-VPN.The most significant advantage of MD-VPN lies in that it requires only the PEdevices to support multiple instances. Multicast VPN can be implemented withoutupgrading any CE devices and P devices, and without changing the original PIMconfiguration of the CE devices and the P device. In other words, the MD-VPNsolution is transparent to the CE devices and the P device.Basic concepts in MD-VPNThe basic concepts involved in MD-VPN are described in Table 49.Table 49 Basic concepts in MD-VPNConcept DescriptionMulticast VPN routingand forwarding (MVRF)Each VPN instance maintains its unicast routing and forwardingtable, which is referred to as VPN routing and forwarding table(VRF). With Layer 3 multicast enabled, a VPN instance also maintainsits multicast routing and forwarding table. The unicast routing andforwarding table and the multicast router and forwarding tablesimultaneously maintained by a VPN instance are referred to as anMVRF in general. Each MVRF can belong to only one MD. DifferentMVRFs join the same MD and are interconnected by means of themulticast tunnel (MT) automatically established in the MD to enablemulticast service between different sites and form a multicast VPNnetwork.Multicast domain (MD) A set of interconnected MVRFs that can send multicast traffic toeach other. Each MD corresponds to a multicast-capable VPN, andall the PE devices interfacing with this VPN belong to this MD.Different VPNs corresponds to different MDs, but one PE can belongto multiple MDs at the same time.Multicast tunnel (MT) The tunnel that interconnect all MVRFs in the MD for deliveringprivate network traffic within the MD. In the perspective of anMVRF, the MT is like a multi-access LAN. Each MVRF access thismulti-access LAN through an MTI.Multicast tunnelinterface (MTI)In perspective of a VPN instance on a PE device, an MT is a virtualinterface, which is referred to as an MTI. Upon share-group and MTIbinding configuration for a VPN instance, an MTI is automaticallycreated per MVRF. It is the entrance to or exit of an MT, orequivalent to an entrance to or exit of an MD. An MVRF uses an MTIto access the MD. In the perspective of an MVRF, an MTI is like aLAN interface, while the MD is like a LAN network, to which all thePE devices are attached. An MTI handles only multicast packets, butnot unicast packets.Share-group In the public network, each MD is assigned an independentmulticast address, which is called share-group. A share-group is theunique identifier of an MD in the public network. It is used to build ashare-MDT corresponding to the MD on the public network. EachMD has a unique share-group.
