Administrative Scoping Overview - HP 6125G Configuration Manual

The RP can periodically check the passing-by IPv4 multicast packets. If it finds that the traffic rate
exceeds a configurable threshold, the RP sends an (S, G) join message hop by hop toward the
multicast source to establish an SPT between the DR at the source side and the RP. Subsequent
multicast data travels along the established SPT to the RP.
For more information about the switchover to SPT initiated by the RP, see
registration."
The receiver-side DR initiates the switchover to SPT.
2.
After receiving the first multicast packet, the receiver-side DR initiates the switchover to SPT, as
follows:
The receiver-side DR sends an (S, G) join message hop by hop toward the multicast source.
When the join message reaches the source-side DR, all the routers on the path have installed
the (S, G) entry in their forwarding table, and thus an SPT branch is established.
When the multicast packets travel to the router where the RPT and the SPT deviate, the router
drops the multicast packets received from the RPT and sends an RP-bit prune message hop by
hop to the RP. After receiving this prune message, the RP sends a prune message toward the
multicast source (suppose only one receiver exists). Thus, the switchover to SPT is completed.
Multicast data is directly sent from the source to the receivers along the SPT.
PIM-SM builds SPTs through the switchover to SPT more economically than PIM-DM does through the
flood-and-prune mechanism.
Assert
PIM-SM uses a similar assert mechanism as PIM-DM does. For more information, see "Assert."

Administrative scoping overview

Division of PIM-SM domains
Typically, a PIM-SM domain contains only one BSR, which is responsible for advertising RP-set
information within the entire PIM-SM domain. The information for all multicast groups is forwarded within
the network scope that the BSR administers. This is called the "non-scoped BSR mechanism."
To implement refined management, you can divide a PIM-SM domain into one global scope zone and
multiple administratively scoped zones (admin-scope zones). This is called the "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.
Admin-scope zones are divided specific to multicast groups. Zone border routers (ZBRs) form the
boundary of the admin-scope zone. Each admin-scope zone maintains one BSR, which serves multicast
groups within a specific range. Multicast protocol packets, such as assert messages and bootstrap
messages, for a specific group range cannot cross the admin-scope zone boundary. Multicast group
ranges that different admin-scope zones serve can be overlapped. A multicast group is valid only within
its local admin-scope zone, and functions as a private group address.
The global scope zone maintains a BSR, which serves the multicast groups that do not belong to any
admin-scope zone.
Relationship between admin-scope zones and the global scope zone
The global scope zone and each admin-scope zone have their own C-RPs and BSRs. These devices are
effective only in their respective zones. That is, BSR election and RP election are implemented
independently. Each admin-scope zone has its own boundary. The multicast information within a zone
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"Multicast source