HP MSR2000/3000/4000 Router Series IP Multicast Configuration Guide

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To eliminate these weaknesses, IPv6 PIM-SM allows an RP or the receiver-side DR to initiate a switchover
to SPT when the traffic rate exceeds a specific threshold:
• The RP initiates a switchover to SPT:
The RP periodically checks the multicast packet forwarding rate. If the RP finds that the traffic rate
exceeds the specified threshold, it sends an (S, G) source-specific join message hop by hop toward
the IPv6 multicast source. The routers along the path from the RP to the IPv6 multicast source
constitute an SPT branch. The subsequent IPv6 multicast data for the IPv6 multicast group can be
forwarded to the RP along the branch without being encapsulated in register messages.
For more information about the switchover to SPT initiated by the RP, see "IPv6 multicast source
regi
stration."
• The receiver-side DR initiates a switchover to SPT:
The receiver-side DR periodically checks the forwarding rate for the multicast packets that the IPv6
multicast source S sends to the IPv6 multicast group G. If the forwarding rate exceeds the specified
threshold, the DR initiates a switchover to SPT, as follows:
a. The receiver-side DR sends an (S, G) source-specific join message hop by hop toward the IPv6
multicast source. The routers along the path from the RP to the source-side DR create an (S, G)
entry in their forwarding table to constitute an SPT branch.
b. When the multicast packets for the IPv6 multicast group are forwarded to the router where the
RPT and the SPT branches, the router drops the multicast packets that reach it along the RPT and
sends a prune message with the RP bit hop by hop to the RP. 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.
c. Finally, the IPv6 multicast source sends the multicast packets for the IPv6 multicast group to the
receiver along the SPT.
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