Operation Manual – MulticastH3C S5500-EI Series Ethernet Switches Chapter 7 PIM Configuration7-113) The subsequent multicast data from the multicast source travels along theestablished SPT to the RP, and then the RP forwards the data along the RPT tothe receivers. When the multicast traffic arrives at the RP along the SPT, the RPsends a register-stop message to the source-side DR by unicast to stop thesource registration process.VI. Switchover from RPT to SPTInitially, multicast traffic flows along an RPT from the RP to the receivers. Because theRPT is not necessarily the tree that has the shortest path, upon receiving the firstmulticast packet along the RPT (by default), or when detecting that the multicast trafficrate reaches a configurable threshold (if so configured), the receiver-side DR initiatesan RPT-to-SPT switchover process, as follows:1) First, the receiver-side DR sends an (S, G) join message hop by hop to themulticast source. When the join message reaches the source-side DR, all therouters on the path have installed the (S, G) entry in their forwarding table, andthus an SPT branch is established.2) Subsequently, the receiver-side DR sends a prune message hop by hop to the RP.Upon receiving this prune message, the RP forwards it toward the multicastsource, thus to implement RPT-to-SPT switchover.After the RPT-to-SPT switchover, multicast data can be directly sent from the source tothe receivers. PIM-SM builds SPTs through RPT-to-SPT switchover more economicallythan PIM-DM does through the “flood and prune” mechanism.VII. AssertPIM-SM uses exactly the same assert mechanism as PIM-DM does. Refer to Assert.7.1.5 Introduction to BSR Admin-scope Regions in PIM-SMI. Division of PIM-SM domainsTypically, a PIM-SM domain contains only one BSR, which is responsible foradvertising RP-set information within the entire PIM-SM domain. The information for allmulticast groups is forwarded within the network scope administered by the BSR.To implement refined management and group-specific services, a PIM-SM domain canbe divided into one global scope zone and multiple BSR administratively scopedregions (BSR admin-scope regions).Specific to particular multicast groups, the BSR administrative scoping mechanismeffectively lessens the management workload of a single-BSR domain and providesgroup-specific services.
