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PIM Overview Configuring PIM
page 7-16 OmniSwitch 6800/6850/9000 Advanced Routing Configuration Guide December 2007
Once the Sender’s DR receives the (S,G) Join message, the DR sends the multicast packets natively along
the Shortest Path Tree. At this point, Router X (the router shown between the Sender’s DR and the
Receiver’s DR) will be receiving two copies of the multicast data—one from the SPT and one from the
RPT. This router drops the packets arriving via the RP tree and forwards only those packets arriving via
the SPT.
An (S, G, RPT) Prune message is sent toward the RP. As a result, traffic destined for this group from this
particular source will no longer be forwarded along the RPT. The RP will still receive traffic from the
Source. If there are no other routers wishing to receive data from the source, the RP will send an
(S, G) Prune message toward the source to stop this unrequested traffic.
Traffic is received on this router
from both the SPT and RPT.
Sender
Receiver
RP
DR
DR
Router X
Sender
Receiver
RP
DR
DR
SPT switchover is enabled at the
last hop DR; the switchover is
initiated upon receiving the first
multicast data packet.
Legend
(S, G, RPT) Prune
Multicast Traffic
(S, G, RPT)
Router X
Prune Message