H3C Technologies H3C S7500E Series Switches - Manual (Page 149)

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message toward the multicast source (suppose only one receiver exists). Thus, SPT
switchover is completed.
z Finally, multicast data is directly sent from the source to the receivers along the SPT.
PIM-SM builds SPTs through SPT switchover 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 details, refer to Assert .
Introduction to Administrative Scoping
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 administered by the BSR. We call this non-scoped BSR
mechanism.
To implement refined management, a PIM-SM domain can be divided into one global scope
zone and multiple administratively scoped zones (admin-scope zones). We call this
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 using private group
addresses.
Admin-scope zones are divided specific to multicast groups. The boundary of the admin-scope
zone is formed by zone border routers (ZBRs). 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 served by different admin-scope zones
can overlap. A multicast group is valid only within its local admin-scope zone, functioning 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 admin-scope zones. Namely, BSR election and RP
election are implemented independently within each admin-scope zone. Each admin-scope
zone has its own boundary. The multicast information cannot cross this border in either
direction. A better understanding of the global scope zone and admin-scope zones should be
based on two aspects: geographical space and group address range.
1) Geographical space
Admin-scope zones are logical zones specific to particular multicast groups. The multicast
packets of these multicast groups are confined within the local admin-scope zone and cannot
cross the boundary of the zone.