Administrator Guide

Figure 48. 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.
• IGMP snooping is supported on all MXL 10/40GbE 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.
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Internet Group Management Protocol (IGMP)
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