H3C Technologies H3C S10500 Series Switches - Manual (Page 155)

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Figure 50 Relationship between admin-scope zones and the global scope zone in group address
ranges
In Figure 50 , 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, a
supplementary relationship exists between the global scope zone and all the admin-scope zones in terms
of group address ranges.
PIM-SSM overview
The source-specific multicast (SSM) model and the any-source multicast (ASM) model are opposites.
Presently, the ASM model includes the PIM-DM and PIM-SM modes. You can implement the SSM model
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 relationships 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 is needed, no RPT is required, no source registration process exists, and the multicast source
discovery protocol (MSDP) is not needed for discovering sources in other PIM domains.
The working 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 “ Neighbor
discovery .”
DR election
PIM-SSM uses the same DR election mechanism as in PIM-SM. See “ DR election .”
Construction of SPT
The decision to build an RPT for PIM-SM or an SPT for PIM-SSM depends on whether the multicast group
the receiver will join falls into the SSM group range (SSM group range reserved by IANA is
232.0.0.0/8).