H3C Technologies H3C S12500-X Series Switches - Manual (Page 80)

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Multicast packets that do not belong to any admin-scoped zones are forwarded in the entire
PIM-SM domain.
• In view of multicast group address ranges:
Each admin-scoped zone is designated to specific multicast groups, of which the multicast group
addresses are valid only within the local zone. The multicast groups of different admin-scoped
zones might have intersections. All the multicast groups other than those of the admin-scoped
zones use the global-scoped zone.
Figure 30 Relationship in view of multicast group address ranges
As shown in Figure 30 , the admin-scoped zones 1 and 2 have no intersection, but the
admin-scoped zone 3 is a subset of the admin-scoped zone 1. The global-scoped zone provides
services for all the multicast groups that are not covered by the admin-scoped zones 1 and 2,
G−G1−G2 in this case.
PIM-SSM overview
The ASM model includes PIM-DM and PIM-SM. The SSM model can be implemented by leveraging part
of the PIM-SM technique. It is also called "PIM-SSM."
The SSM model provides a solution for source-specific multicast. It maintains the relationship between
hosts and routers through IGMPv3.
In actual applications, part of IGMPv3 and PIM-SM techniques are adopted to implement the SSM model.
In the SSM model, because receivers have located a multicast source, no RP or RPT is required and
multicast sources do not register for discovering multicast sources in other PIM domains.
The operating mechanism of PIM-SSM is summarized as follows:
• Neighbor discovery
• DR election
• SPT building
Neighbor discovery
PIM-SSM uses the same neighbor discovery mechanism as PIM-SM. For more information, see
"
Neighbor discovery ."
DR election
PIM-SSM uses the same DR election mechanism as PIM-SM. For more information, see " DR election ."