91
Figure 40 Relationship in view of multicast group address ranges
As shown in Figure 40, 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, multicast receivers have already located the multicast sources. 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
When a receiver joins a multicast group, the receiver-side DR uses the SSM group range to determine
whether to build an RPT for PIM-SM or an SPT for PIM-SSM. 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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