Operation Manual – Multicast ProtocolH3C S3610&S5510 Series Ethernet Switches Chapter 6 PIM Configuration6-11a supplementary relationship between the global scope zone and all the BSRadmin-scope regions in terms of group address ranges.Relationships between BSR admin-scope regions and the global scope zone are asfollows:z The global scope zone and each BSR admin-scope region have their own C-RPsand BSR. These devices are effective only in their respective admin-scope regions.Namely, the BSR election and RP election are implemented independently withineach admin-scope region.z Each BSR admin-scope region has its own boundary. The multicast information(such as C-RP-Adv messages and BSR bootstrap messages) can be transmittedonly within the domain.z Likewise, the multicast information in the global scope zone cannot enter any BSRadmin-cope region.z In terms of multicast information propagation, BSR admin-scope regions areindependent of one another and each BSR admin-scope region is independent ofthe global scope zone, and no overlapping is allowed between any two BSRadmin-scope regions.6.1.6 SSM Model Implementation in PIMThe source-specific multicast (SSM) model and the any-source multicast (ASM) modelare two opposite models. Presently, the ASM model includes the PIM-DM and PIM-SMmodes. The SSM model can be implemented by leveraging part of the PIM-SMtechnique.The SSM model provides a solution for source-specific multicast. It maintains therelationships between hosts and routers through IGMPv3. PIM-DM implementsmulticast forwarding by building SPTs rooted at the multicast source through the “floodand prune” mechanism. Although an SPT has the shortest path, it is built in a lowefficiency. Therefore the PIM-DM mod is not suitable for large- and medium-sizednetworks.In actual application, part of the PIM-SM technique is adopted to implement the SSMmodel. In the SSM model, receivers know exactly where a multicast source is locatedby means of advertisements, consultancy and so on. Therefore, no RP is needed, noRPT is required, there is no source registration process, and there is no need of usingthe multicast source discovery protocol (MSDP) for discovering sources in other PIMdomains.The SSM model only needs the support of IGMPv3 and some subsets of PIM-SM. Theoperation mechanism of PIM-SSM can be summarized as follows:z Neighbor discoveryz DR electionz SPT building
