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Figure 48 RPT building at the multicast source side
As shown in Figure 48, 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 * 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.
NOTE:
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, multicast packets from the
multicast source to the receiver are directly forwarded by the node to the receiver, instead of by the RP.
Administrative scoping overview
Division of PIM-SM domains
Typically, a PIM-SM domain or BIDIR-PIM domain contains only one BSR, which 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."
Source
Server A
Server B
Host B
Host C
Receiver
Receiver
Multicast packets
Source-side RPT
RP
Source
Host A
Receiver
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