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Admin-scoped zones are divided for multicast groups. Zone border routers (ZBRs) form the boundary of
an admin-scoped zone. Each admin-scoped zone maintains one BSR for multicast groups within a
specific range. Multicast protocol packets, such as assert messages and BSMs, for a specific group range
cannot cross the boundary of the admin-scoped zone for the group range. Multicast group ranges that
are associated with different admin-scoped zones can have intersections. However, the multicast groups
in an admin-scoped zone are valid only within the local zone, and theses multicast groups are regarded
as private group addresses.
The global-scoped zone maintains a BSR for the multicast groups that do not belong to any
admin-scoped zones.
Relationship between admin-scoped zones and the global-scoped zone
The global-scoped zone and each admin-scoped zone have their own C-RPs and BSRs. These devices are
effective only on their respective zones, and the BSR election and the RP election are implemented
independently. Each admin-scoped zone has its own boundary. The multicast information within a zone
cannot cross this boundary in either direction. You can have a better understanding of the global-scoped
zone and admin-scoped zones based on geographical locations and multicast group address ranges.
• In view of geographical locations:
An admin-scoped zone is a logical zone for particular multicast groups. The multicast packets for
such multicast groups are confined within the local admin-scoped zone and cannot cross the
boundary of the zone.
Figure 39 Relationship in view of geographical locations
As shown in Figure 39, for the multicast groups in a specific group address range, the
admin-scoped zones must be geographically separated and isolated. A router cannot belong to
multiple admin-scoped zones. An admin-scoped zone contains routers that are different from other
admin-scoped zones. However, the global-scoped zone includes all routers in the PIM-SM domain
or BIDIR-PIM domain. Multicast packets that do not belong to any admin-scoped zones are
forwarded in the entire PIM-SM domain or BIDIR-PIM domain.
• In view of multicast group address ranges:
Each admin-scoped zone is designated to specific multicast groups, of which the multicast group
addresses are valid only within the local zone. The multicast groups of different admin-scoped
zones might have intersections. All the multicast groups other than those of the admin-scoped
zones use the global-scoped zone.
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