H3C Technologies H3C SecPath F1000-E - Manual (Page 176)

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advertisements, consultancy, and so on. Therefore, no RP is needed, no RPT is required, and is no source
registration process is needed for the purpose of discovering IPv6 multicast sources in other IPv6 PIM
domains.
Compared with the ASM model, the SSM model only needs the support of MLDv2 and some subsets of
IPv6 PIM-SM. The operation mechanism of the SSM model in an IPv6 PIM domain can be summarized
as follows:
• Neighbor discovery
• DR election
• SPT building
Neighbor discovery
IPv6 PIM-SSM uses the same neighbor discovery mechanism as in IPv6 PIM-SM. For more information,
see Neighbor discovery .
DR election
IPv6 PIM-SSM uses the same DR election mechanism as in IPv6 PIM-SM. For more information, see DR
election .
SPT building
Whether to build an RPT for IPv6 PIM-SM or an SPT for IPv6 PIM-SSM depends on whether the IPv6
multicast group the receiver is to join falls in the IPv6 SSM group range (the IPv6 SSM group range
reserved by IANA is FF3x::/32, where x represents any legal address scope).
Figure 9 Building an SPT in IPv6 PIM-SSM
As shown in
Figure 9 , Hosts B and C are IPv6 multicast information receivers. They send an MLDv2 report
message to the respective DRs to announce that they are interested in the information of the specific IPv6
multicast source S and that sent to the IPv6 multicast group G.
The DR that has received the report first checks whether the IPv6 group address in this message falls in
the IPv6 SSM group range:
• If so, the IPv6 PIM-SSM model is built: the DR sends a channel subscription message hop by hop
toward the IPv6 multicast source S. An (S, G) entry is created on all routers on the path from the DR