94
Figure 42 Relationship in view of multicast group address ranges
As shown in Figure 42, 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. Multicast
sources do not register, and the MSDP is not needed for discovering multicast sources in other PIM
domains.
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."
SPT building
The decision to build an RPT for PIM-SM or an SPT for PIM-SSM depends on whether the multicast group
that the receiver joins is in the SSM group range. The SSM group range reserved by IANA is
232.0.0.0/8.
Admin-scope 3
G3 address
Admin-scope 2
G2 address
Admin-scope 1
G1 address
Global-scope
G
−G1−G2 address
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