Reference Guide

PIM Sparse-Mode | 723
Configuration Notes and Restrictions
The following conditions apply when you configure and use PIM snooping on a switch:
• PIM-SM snooping is deployed in a Layer 2 environment and is mutually exclusive with PIM multicast
routing. If you enable PIM-SM snooping, you cannot enable PIM-SM or PIM-DM. If you enable
PIM-SM snooping, you cannot enable PIM-SM or PIM-DM
• PIM-SM snooping is supported with IGMP snooping, and forwards the IGMP report on the port that
connects to the PIM DR.
It is recommended that you do not enable IGMP snooping on a PIM-SM snooping-enabled VLAN
interface unless until it is necessary for VLAN operation.
For information on the egress ports used for outgoing multicast traffic when you enable PIM-SM
snooping and IGMP snooping at the same time on a VLAN interface, refer to PIM-SM and IGMP
Snooping: Usage Notes.
• PIM-SM snooping listens to PIM hello and PIM-SM join and prune messages while maintaining the
VLAN- and port-specific information in multicast packets that are snooped.
PIM-SM Snooping Example
Figure 37-1 shows an example with PIM-SM snooping enabled. When Router A sends a join message to
Router B, the switches forward the join message only to Router B without flooding the message to other
connected routers, such as Routers C and D.
Figure 37-1. PIM-SM Snooping: Join Message Flow
Router A
(*,G) PIM join
IGMP join
Receiver
Router C
Router D
Router B
RP Source
Layer 2 Network
with PIM Snooping