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Figure 48 RPT building at the multicast source side
As shown in
, the process for building a source-side RPT is relatively simple:
1.
When a multicast source sends multicast packets to multicast group G, the DF in each network
segment unconditionally forwards the packets to the RP.
2.
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 asterisk (*)
means any multicast source.
After a bidirectional RPT is built, multicast traffic is forwarded along the source-side RPT and
receiver-side RPT from sources to receivers.
If a receiver and a 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 multicast packets
that the multicast source sends to the receiver are directly forwarded by the node to the receiver,
instead of by the RP.
Administrative scoping
This section describes division of PIM-SM domains and relationship between admin-scoped zones
and the global-scoped zone.
Division of PIM-SM domains
Typically, a PIM-SM domain or BIDIR-PIM domain contains only one BSR. The BSR is responsible
for advertising RP-set information within the entire PIM-SM/BIDIR-PIM domain. The information for
all multicast groups is forwarded within the network scope that the BSR administers. This is called
the "non-scoped BSR mechanism."
To implement refined management, you can divide a PIM-SM domain or BIDIR-PIM domain into one
global scope zone and multiple administratively scoped zones (admin-scope zones). This is called
the "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.
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
