Concept Guide

IGMP Snooping
IGMP snooping enables switches to use information in IGMP packets to generate a forwarding table that associates ports with multicast
groups so that when they receive multicast frames, they can forward them only to interested receivers.
Multicast packets are addressed with multicast MAC addresses, which represent a group of devices, rather than one unique device.
Switches forward multicast frames out of all ports in a virtual local area network (VLAN) by default, even though there may be only some
interested hosts, which is a waste of bandwidth.
If you enable IGMP snooping on a VLT unit, IGMP snooping dynamically learned groups and multicast router ports are made to learn on the
peer by explicitly tunneling the received IGMP control packets.
IGMP Snooping Implementation Information
• IGMP snooping on Dell EMC Networking OS uses IP multicast addresses not MAC addresses.
• IGMP snooping reacts to spanning tree protocol (STP) and multiple spanning tree protocol (MSTP) topology changes by sending a
general query on the interface that transitions to the forwarding state.
• If IGMP snooping is enabled on a PIM-enabled VLAN interface, data packets using the router as an Layer 2 hop may be dropped. To
avoid this scenario, Dell EMC Networking recommends that users enable IGMP snooping on server-facing end-point VLANs only.
Conguring IGMP Snooping
Conguring IGMP snooping is a one-step process. To enable, view, or disable IGMP snooping, use the following commands.
There is no specic conguration needed for IGMP snooping with virtual link trunking (VLT). For information about VLT congurations,
refer to
Virtual Link Trunking (VLT).
• Enable IGMP snooping on a switch.
CONFIGURATION mode
ip igmp snooping enable
• View the conguration.
CONFIGURATION mode
show running-config
• Disable snooping on a VLAN.
INTERFACE VLAN mode
no ip igmp snooping
Related Conguration Tasks
• Removing a Group-Port Association
• Disabling Multicast Flooding
• Specifying a Port as Connected to a Multicast Router
• Conguring the Switch as Querier
Example of ip igmp snooping enable Command
DellEMC(conf)#ip igmp snooping enable
DellEMC(conf)#do show running-config igmp
ip igmp snooping enable
DellEMC(conf)#
Internet Group Management Protocol (IGMP)
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