Glossary

Table Of Contents
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 is supported on all stack members.
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.
Configuring IGMP Snooping
Configuring IGMP snooping is a one-step process. To enable, view, or disable IGMP snooping, use the following commands.
There is no specific configuration needed for IGMP snooping with virtual link trunking (VLT). For information about VLT
configurations, refer to Virtual Link Trunking (VLT).
Enable IGMP snooping on a switch.
CONFIGURATION mode
ip igmp snooping enable
View the configuration.
CONFIGURATION mode
show running-config
Disable snooping on a VLAN.
INTERFACE VLAN mode
no ip igmp snooping
Related Configuration Tasks
Removing a Group-Port Association
Disabling Multicast Flooding
Specifying a Port as Connected to a Multicast Router
Configuring the Switch as Querier
DellEMC(conf)#ip igmp snooping enable
DellEMC(conf)#do show running-config igmp
ip igmp snooping enable
DellEMC(conf)#
Removing a Group-Port Association
To configure or view the remove a group-port association feature, use the following commands.
Configure the switch to remove a group-port association after receiving an IGMP Leave message.
INTERFACE VLAN mode
ip igmp fast-leave
Internet Group Management Protocol (IGMP)
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