Reference Guide

EXEC Privilege mode
show ip igmp interface
View the enable status of this feature using the command from EXEC Privilege mode, as shown in the example in
Selecting an IGMP Version.
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 FTOS uses IP multicast addresses not MAC addresses.
• IGMP snooping is supported on all S4820T 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 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
354