Figure 47. Membership Queries: Leaving and Staying
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 the Dell Networking OS uses IP multicast addresses not MAC addresses.
• IGMP snooping is not supported on stacked VLANs.
Internet Group Management Protocol (IGMP) 393