H3C Technologies H3C S12500-X Series Switches - Manual (Page 163)

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multicast source constitute an SPT. The subsequent IPv6 multicast data is forwarded to the RP along
the SPT without being encapsulated into register messages.
For more information about the switchover to SPT initiated by the RP, see "
Multicast source
registration ."
• The receiver-side DR initiates a switchover to SPT:
After receiving the first (S, G) multicast packet, the receiver-side DR initiates a switchover to SPT
immediately, as follows:
a. The receiver-side DR sends an (S, G) source-specific join message toward the IPv6 multicast
source. The routers along the path create an (S, G) entry in their forwarding table to constitute
an SPT.
b. When the multicast packets reach the router where the RPT and the SPT branches, the router
drops the multicast packets that travel along the RPT. It then sends a prune message with the RP
bit toward the RP.
c. After receiving the prune message, the RP forwards it toward the IPv6 multicast source
(supposed only one receiver exists). Thus, the switchover to SPT is completed. The subsequent
IPv6 multicast packets travel along the SPT from the IPv6 multicast source to the receiver hosts.
With the switchover to SPT, IPv6 PIM-SM builds SPTs more economically than IPv6 PIM-DM does.
Assert
IPv6 PIM-SM uses a similar assert mechanism as IPv6 PIM-DM does. For more information, see " Assert ."
IPv6 administrative scoping overview
Typically, an IPv6 PIM-SM domain contains only one BSR, which is responsible for advertising RP-set
information within the entire IPv6 PIM-SM domain. Information about all IPv6 multicast groups is
forwarded within the network that the BSR administers. This is called the "IPv6 non-scoped BSR
mechanism."
IPv6 administrative scoping mechanism
To implement refined management, you can divide an IPv6 PIM-SM domain into an IPv6 global-scoped
zone and multiple IPv6 administratively-scoped zones (admin-scoped zones). This is called the "IPv6
administrative scoping mechanism."
The administrative scoping mechanism effectively releases stress on the management in a single-BSR
domain and enables provision of zone-specific services through private group addresses.
An IPv6 admin-scoped zone is designated to particular IPv6 multicast groups with the same scope field
value in their group addresses. Zone border routers (ZBRs) form the boundary of an IPv6 admin-scoped
zone. Each IPv6 admin-scoped zone maintains one BSR for IPv6 multicast groups with the same scope
field value. IPv6 multicast protocol packets, such as assert messages and BSMs, of these IPv6 multicast
groups cannot cross the boundary of the IPv6 admin-scoped zone for the group range. The IPv6 multicast
group ranges to which different IPv6 admin-scoped zones are designated can have intersections, but the
IPv6 multicast groups in an IPv6 admin-scoped zone are valid only within its local zone, and theses IPv6
multicast groups are regarded as private group addresses.
The IPv6 global-scoped zone can be regarded as a special IPv6 admin-scoped zone, and it maintains a
BSR for the IPv6 multicast groups with the scope field value as 14.