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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 within each admin-scope zone. Each admin-scope zone has its own boundary. The

multicast information cannot cross this boundary in either direction. A better understanding of the global-

scope zone and admin-scope zones should be based on 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.

Figure 45 Relationship between admin-scope zones and the global-scope zone in geographic space

As shown in Figure 45, for multicast groups in the same address range, admin-scope zones must be

geographically separated from one another. Namely, a router must not serve different admin-scope

zones. Different admin-scope zones contain different routers, whereas the global-scope zone covers all

routers in the PIM-SM/BIDIR-PIM domain. Multicast packets that do not belong to any admin-scope zones

can be transmitted in the entire PIM-SM/BIDIR-PIM domain.

2. Multicast group address ranges

In terms of multicast group address ranges, each admin-scope zone serves specific multicast groups.

Usually, these addresses have no intersections. However, they might overlap one another.

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