H3C Technologies H3C S7500E Series Switches - Manual (Page 151)

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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:
z Neighbor discovery
z DR election
z SPT building
Neighbor discovery
PIM-SSM uses the same neighbor discovery mechanism as in PIM-DM and PIM-SM. Refer to
Neighbor discovery .
DR election
PIM-SSM uses the same DR election mechanism as in PIM-SM. Refer to 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).
Figure 6-9 SPT establishment in PIM-SSM