Users Guide

Enabling IGMP Immediate-Leave
If the querier does not receive a response to a group-specic or group-and-source query, it sends another (querier robustness value). Then,
after no response, it removes the group from the outgoing interface for the subnet.
IGMP immediate leave reduces leave latency by enabling a router to immediately delete the group membership on an interface after
receiving a Leave message (it does not send any group-specic or group-and-source queries before deleting the entry).
• Congure the system for IGMP immediate leave.
ip igmp immediate-leave
• View the enable status of the IGMP immediate leave feature.
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 Dell 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 Networking recommends that users enable IGMP snooping on server-facing end-point VLANs only.
Conguring IGMP Snooping
Conguring IGMP snooping is a one-step process. To enable, view, or disable IGMP snooping, use the following commands.
There is no specic conguration needed for IGMP snooping with virtual link trunking (VLT). For information about VLT congurations,
refer to Virtual Link Trunking (VLT).
• Enable IGMP snooping on a switch.
CONFIGURATION mode
ip igmp snooping enable
• View the conguration.
CONFIGURATION mode
show running-config
Internet Group Management Protocol (IGMP)
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