IPv6 PIM Overview 1245Figure 364 Building an SPT in IPv6 PIM-SSMAs shown in Figure 364, Hosts B and C are IPv6 multicast information receivers.They send an MLDv2 report message marked (include S, G) to the respective DRsto announce that they are interested in the information of the specific IPv6multicast source S and that sent to the IPv6 multicast group G. If they needinformation from other sources than S, they send an (exclude S, G) report. Nomatter what the description is, the position of IPv6 multicast source S is explicitlyspecified for receivers.The DR that has received the report first checks whether the IPv6 group address inthis message falls in the IPv6 SSM group address range:■ If so, the IPv6 PIM-SSM model is built: the DR sends a channel subscriptionmessage hop by hop toward the IPv6 multicast source S. An (include S, G) or(exclude S, G) entry is created on all routers on the path from the DR to thesource. Thus, an SPT is built in the network, with the source S as its root andreceivers as its leaves. This SPT is the transmission channel in IPv6 PIM-SSM.■ If not, the IPv6 PIM-SM process is followed: the DR needs to send a (*, G) joinmessage to the RP, and an IPv6 multicast source registration process is needed.n In IPv6 PIM-SSM, the “channel” concept is used to refer to an IPv6 multicast group,and the “channel subscription” concept is used to refer to a join message.Protocols and Standards IPv6 PIM-related specifications are as follows:■ RFC 2362: Protocol Independent Multicast-sparse Mode(PIM-SM):ProtocolSpecification■ RFC 3973: Protocol Independent Multicast-Dense Mode(PIM-DM):ProtocolSpecification(Revised)■ RFC 3956: Embedding the Rendezvous Point (RP) Address in an IPv6 MulticastAddress■ draft-ietf-pim-sm-v2-new-06: Protocol Independent Multicast-Sparse Mode(PIM-SM)SourceServerHost AHost BHost CReceiverReceiverIPv6 multicast packetsSPTSubscribe messageRP DRDR
