308
Figure 90
RPT building at the multicast source side
As shown in
, the process of building a source-side RPT is relatively simple:
4.
When an IPv6 multicast source sends IPv6 multicast packets to IPv6 multicast group G, the DF in
each network segment unconditionally forwards the packets to the RP.
5.
The routers along the path from the source's directly connected router to the RP form an RPT branch.
Each router on this branch adds a (*, G) entry to its forwarding table. The * means any IPv6
multicast source.
After a bidirectional RPT is built, multicast traffic is forwarded along the source-side RPT and receiver-side
RPT from IPv6 multicast sources to receivers.
If a receiver and an IPv6 multicast source are at the same side of the RP, the source-side RPT and the
receiver-side RPT might meet at a node before reaching the RP. In this case, the IPv6 multicast packets that
the IPv6 multicast source sends to the receiver are directly forwarded by the node to the receiver, instead
of by the RP.
IPv6 administrative scoping overview
Typically, an IPv6 PIM-SM domain or IPv6 BIDIR-PIM domain contains only one BSR, which is responsible
for advertising RP-set information within the entire IPv6 PIM-SM/IPv6 BIDIR-PIM domain. The information
for all multicast groups is forwarded within the network scope administered by the BSR. This is called the
"IPv6 non-scoped BSR mechanism."
To implement refined management, an IPv6 PIM-SM/IPv6 BIDIR-PIM domain can be divided into one
IPv6 global-scoped zone and multiple IPv6 administratively scoped zones (IPv6 admin-scoped zones).
This is called the "IPv6 administrative scoping mechanism."
The IPv6 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.
IPv6 admin-scoped zones correspond to IPv6 multicast groups with different scope values in their group
addresses. The boundary of the IPv6 admin-scoped zone is formed by zone border routers (ZBRs). Each
IPv6 admin-scoped zone maintains one BSR, which serves multicast groups within a specific scope. IPv6
multicast protocol packets, such as assert messages and bootstrap messages, for a specific group range
