IPv6 administrative scoping

Typically, an IPv6 PIM-SM domain or an IPv6 BIDIR-PIM domain contains only one BSR, which is responsible for advertising RP-set information within the entire 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."

To implement refined management, you can divide an IPv6 PIM-SM domain or IPv6 BIDIR-PIM 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 group ranges to which different IPv6 admin-scoped zones are designated can have intersections. However, the IPv6 multicast groups in an IPv6 admin-scoped zone are valid only within its local zone, and theses IPv6 multicast groups are regarded as private group addresses.

The IPv6 global-scoped zone can be regarded as a special IPv6 admin-scoped zone, and it maintains a BSR for the IPv6 multicast groups with the scope field value as 14.

The IPv6 global-scoped zone and each IPv6 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 IPv6 admin-scoped zone has its own boundary. The IPv6 multicast information within a zone cannot cross this boundary in either direction. You can have a better understanding of the IPv6 global-scoped zone and IPv6 admin-scoped zones based on geographical locations and the scope field values.

• In view of geographical locations:

  An IPv6 admin-scoped zone is a logical zone for particular IPv6 multicast groups with the same scope field value. The IPv6 multicast packets for such IPv6 multicast groups are confined within the local IPv6 admin-scoped zone and cannot cross the boundary of the zone.

  Figure 116: Relationship in view of geographical locations

  

  As shown in Figure 116, for the IPv6 multicast groups with the same scope field value, the IPv6 admin-scoped zones must be geographically separated and isolated. The IPv6 global-scoped zone includes all devices in the IPv6 PIM-SM domain or IPv6 BIDIR-PIM domain. IPv6 multicast packets that do not belong to any IPv6 admin-scoped zones are forwarded in the entire IPv6 PIM-SM domain or IPv6 BIDIR-PIM domain.

• In view of the scope field values:

  In terms of the scope field values, the scope field in an IPv6 multicast group address shows the zone to which the IPv6 multicast group belongs.

  Figure 117: IPv6 multicast address format

  

  An IPv6 admin-scoped zone with a larger scope field value contains an IPv6 admin-scoped zone with a smaller scope field value. The zone with the scope field value of E is the IPv6 global-scoped zone. Table 23 lists the possible values of the scope field.

  Table 23: Values of the Scope field

  Value	Meaning	Remarks
  0, F	Reserved	N/A
  1	Interface-local scope	N/A
  2	Link-local scope	N/A
  3	Subnet-local scope	IPv6 admin-scoped zone.
  4	Admin-local scope	IPv6 admin-scoped zone.
  5	Site-local scope	IPv6 admin-scoped zone.
  6, 7, 9 through D	Unassigned	IPv6 admin-scoped zone.
  8	Organization-local scope	IPv6 admin-scoped zone.
  E	Global scope	IPv6 global-scoped zone.