Users 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 Networking OS uses IP multicast addresses not MAC addresses.
• GMP snooping is supported on all S5000 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.
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
• Enabling IGMP Immediate-Leave
• Disabling Multicast Flooding
• Specifying a Port as Connected to a Multicast Router
• Configuring the Switch as Querier
Internet Group Management Protocol (IGMP) 457