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Configuring PIM snooping
Overview
PIM snooping runs on Layer 2 devices. It works with IGMP snooping to analyze received PIM
messages, and adds the ports that are interested in specific multicast data to a PIM snooping routing
entry. In this way, the multicast data can be forwarded to only the ports that are interested in the data.
Figure 15 Multicast packet transmission without or with PIM snooping
As shown in Figure 15, Source 1 sends multicast data to multicast group G1, and Source 2 sends
multicast data to multicast group G2. Receiver 1 belongs to G1, and Receiver 2 belongs to G2. The
Layer 2 switch's interfaces that connect to the PIM routers are in the same VLAN.
• When the Layer 2 switch runs only IGMP snooping, it performs the following actions:
a. Maintains the router ports according to the received PIM hello messages that PIM routers
send.
b. Broadcasts all other types of received PIM messages except PIM hello messages in the
VLAN.
c. Forwards all multicast data to all router ports in the VLAN.
Multicast packet transmission
when only IGMP snooping runs
Multicast packet transmission when
IGMP snooping and PIM snooping both run
Source 1
Source 2
Receiver 1 Receiver 2
Multicast packets (S1, G1) Join message (S1, G1)
Layer 2 switch
Source 1 Source 2
Receiver 1 Receiver 2
Layer 2 switch
Multicast packets (S2, G2) Join message (S2, G2)
PIM
router 3
PIM
router 1
PIM
router 2
PIM
router 4
PIM
router 3
PIM
router 1
PIM
router 2
PIM
router 4
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