H3C Technologies H3C SecPath F1000-E - Manual (Page 108)

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Figure 8 Relationship between admin-scope zones and the global scope zone in group address ranges
In
Figure 8 , the group address ranges of admin-scope 1 and 2 have no intersection, whereas the group
address range of admin-scope 3 is a subset of the address range of admin-scope 1. The group address
range of the global scope zone covers all the group addresses other than those of all the admin-scope
zones. That is, the group address range of the global scope zone is G-G1-G2. In other words, there is a
supplementary relationship between the global scope zone and all the admin-scope zones in terms of
group address ranges.
SSM Model Implementation in PIM
The source-specific multicast (SSM) model and the any-source multicast (ASM) model are two opposite
models. Presently, 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.
The SSM model provides a solution for source-specific multicast. It maintains the relationships between
hosts and routers through IGMPv3.
In actual application, part of the PIM-SM technique is adopted to implement the SSM model. In the SSM
model, receivers know exactly where a multicast source is located by means of advertisements,
consultancy, and so on. Therefore, no RP is needed, no RPT is required, there is no source registration
process, and there is no need of using the multicast source discovery protocol (MSDP) for discovering
sources in other PIM domains.
Compared with the ASM model, the SSM model only needs the support of IGMPv3 and some subsets of
PIM-SM. The operation mechanism of PIM-SSM can be 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. For more information,
see Neighbor discovery .
DR election
PIM-SSM uses the same DR election mechanism as in PIM-SM. For more information, see DR election .
Construction of SPT
Whether to build an RPT for PIM-SM or an SPT for PIM-SSM depends on whether the multicast group the
receiver is to join falls in the SSM group range (SSM group range reserved by IANA is 232.0.0.0/8).