54
Figure 28
Relationship in view of multicast group address ranges
As shown in
, 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 serves all
the multicast groups that are not covered by the admin-scoped zones 1 and 2, that is, G
−
G1
−
G2
in this case.
PIM-SSM overview
The SSM model and the ASM model are opposites. The ASM model includes the PIM-DM and PIM-SM
modes. 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 application, part of IGMPv3 or PIM-SM technique is adopted to implement the SSM model. In
the SSM model, receivers locate a multicast source by means of advertisements, consultancy, and so on.
No RP or RPT is required, no source registration process exists, and the MSDP is not needed for
discovering 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 in PIM-DM and PIM-SM. See "
DR election
PIM-SSM uses the same DR election mechanism as in PIM-SM. See "
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 will join falls into the SSM group range (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
