Deployment Guide

IGMP Snooping
IGMP snooping is auto-congured on an Aggregator.
Multicast packets are addressed with multicast MAC addresses, which represents a group of devices rather than one unique device.
Switches forward multicast frames out of all ports in a VLAN by default, even if there are only a small number of interested hosts, resulting
in a waste of bandwidth. IGMP snooping enables switches to use information in IGMP packets to generate a forwarding table that
associate ports with multicast groups, so that the received multicast frames are forwarded only to interested receivers.
How IGMP Snooping is Implemented on an
Aggregator
• IGMP snooping is enabled by default on the switch.
• Dell Networking OS supports version 1, version 2 and version 3 hosts.
• Dell Networking OS — IGMP snooping is based on the IP multicast address (not on the Layer 2 multicast MAC address). IGMP
snooping entries are stored in the Layer 3 ow table instead of in the Layer 2 forwarding information base (FIB).
• Dell Networking OS — IGMP snooping is based on draft-ietf-magma-snoop-10.
• A maximum of 2k groups and 4k virtual local area networks (VLAN) are supported.
• IGMP snooping is not supported on the default VLAN interface.
• Flooding of unregistered multicast trac is enabled by default.
• Queries are not accepted from the server side ports and are only accepted from the uplink LAG.
• Reports and Leaves are ooded by default to the uplink LAG irrespective of whether it is an mrouter port or not.
Disabling Multicast Flooding
If the switch receives a multicast packet that has an IP address of a group it has not learned (unregistered frame), the switch oods that
packet out of all ports on the VLAN. To disable multicast ooding on all VLAN ports, enter the no ip igmp snooping ood command in
global conguration mode.
When multicast ooding is disabled, unregistered multicast data trac is forwarded to only multicast router ports on all VLANs. If there is
no multicast router port in a VLAN, unregistered multicast data trac is dropped.
Displaying IGMP Information
Use the show commands from the below table, to display information on IGMP. If you specify a group address or interface:
• Enter a group address in dotted decimal format; for example, 225.0.0.0.
• Enter an interface in one of the following formats: tengigabitethernet slot/port, port-channel port-channel-
number, or vlan vlan-number.
Displaying IGMP Information
Command
Output
show ip igmp
snooping
groups [group-
address
[detail] |
detail |
interface
[group-address
[detail]]
Displays information on IGMP groups.
Internet Group Management Protocol (IGMP) 343