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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 31 Configuring PIM Snooping
Understanding How PIM Snooping Works
Note To use PIM snooping, you must enable IGMP snooping on the Cisco 7600 series router. IGMP snooping
restricts multicast traffic that exits through the LAN ports to which hosts are connected. IGMP snooping
does not restrict traffic that exits through the LAN ports to which one or more multicast routers are
connected.
The following illustrations show the flow of traffic and flooding that results in networks without PIM
snooping enabled and the flow of traffic and traffic restriction when PIM snooping is enabled.
Figure 31-1 shows the flow of a PIM join message without PIM snooping enabled. In the figure, the
switches flood the PIM join message intended for Router B to all connected routers.
Figure 31-1 PIM Join Message Flow without PIM Snooping
\
Figure 31-2 shows the flow of a PIM join message with PIM snooping enabled. In the figure, the
switches restrict the PIM join message and forward it only to the router that needs to receive it (Router
B).
Router C Router D
Router BRouter A
(*, G) PIM join
RP Source
Receiver
IGMP join
99473
SP network
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