CCIE RS – Written – L2 Multicast – Explain PIM Snooping

PIM Snooping

Switch restricts multicast packets for each IP multicast group to only those multicast router ports that have downstream receivers joined to that group

  • Learn within specific VLAN listening to PIM hello messages, PIM join and prune and Bidrectional PIM designated forwarder election
  • Must enable IGMP snooping on switch to use PIM snooping
  • IGMP snooping restricts multicast traffic that exits through the LAN port to which hosts are connected
  • IGMP snooping does not restrict traffic that exists through the LAN ports to which one or more multicast routers are connected


Disabled by default

  • Must use PIM-SM
  • Dense mode is seen as unknown traffic and is dropped
  • Auto-RP groups ( and is always flooded
  • Can enable and disable on per-VLAN basis



  • Ip pim snooping – Global or under vlan interface
  • Show ip pim snooping


Router(config)# ip pim snooping 
Router# show ip pim snooping
Global runtime mode: Enabled
Global admin modeĀ  : Enabled
Number of user enabled VLANs: 1
User enabled VLANs: 10

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