H3C Technologies H3C SecPath F1000-E - Manual (Page 109)

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Figure 9 SPT building in PIM-SSM
As shown in
Figure 9 , Host B and Host C are multicast information receivers. They send IGMPv3 report
messages to the respective DRs to express their interest in the information of the specific multicast source
S.
Upon receiving a report message, the DR first checks whether the group address in this message falls in
the SSM group range:
• If so, the DR sends a subscribe message for channel subscription hop by hop towards the multicast
source S. An (S, G) entry is created on all routers on the path from the DR to the source. Thus, an SPT
is built in the network, with the source S as its root and receivers as its leaves. This SPT is the
transmission channel in PIM-SSM.
• If not, the PIM-SM process is followed: the DR needs to send a (*, G) join message to the RP, and
a multicast source registration process is needed.
NOTE:
In PIM-SSM, the “channel” concept is used to refer to a multicast group, and the “channel
subscription” concept is used to refer to a join message.
Protocols and Standards
PIM-related specifications are as follows:
• RFC 4601: Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification (Revised)
• RFC 3973: Protocol Independent Multicast-Dense Mode (PIM-DM): Protocol Specification(Revised)
• RFC 4607: Source-Specific Multicast for IP
• RFC 5059: Bootstrap Router (BSR) Mechanism for Protocol Independent Multicast (PIM)
• Draft-ietf-ssm-overview-05: An Overview of Source-Specific Multicast (SSM)