3Com WX3000 operation manual Configuring Igmp Querier, Igmp-snooping group-limit limit

Follow these steps to configure the maximum number of multicast groups on a port:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Enter Ethernet port view	interface interface-type	—
	interface-number
Limit the number of multicast	igmp-snooping group-limit limit	Required
		The system default for
groups on a port	[ vlan vlan-list[ overflow-replace ] ]
		the device is 256.

zTo prevent bursting traffic in the network or performance deterioration of the device caused by excessive multicast groups, you can set the maximum number of multicast groups that the device should process.

zWhen the number of multicast groups exceeds the configured limit, the device removes its multicast forwarding entries starting from the oldest one. In this case, the multicast packets for the removed multicast group(s) will be flooded in the VLAN as unknown multicast packets. As a result, non-member ports can receive multicast packets within a period of time. To avoid this from happening, enable the function of dropping unknown multicast packets.

Configuring IGMP Querier

In an IP multicast network running IGMP, a multicast router or Layer 3 multicast device is responsible for sending IGMP general queries, so that all Layer 3 multicast devices can establish and maintain multicast forwarding entries, thus to forward multicast traffic correctly at the network layer. This router or Layer 3 device is called IGMP querier.

However, a Layer 2 multicast device does not support IGMP, and therefore cannot send general queries by default. By enabling IGMP Snooping on a Layer 2 device in a VLAN where multicast traffic needs to be Layer-2 switched only and no multicast routers are present, the Layer 2 device will act as the IGMP Snooping querier to send IGMP general queries, thus allowing multicast forwarding entries to be established and maintained at the data link layer.

You can also configure the source address, maximum response time and interval of general queries to be sent from the IGMP Snooping querier.

Follow these steps to configure IGMP Snooping querier:

To do…	Use the command…	Remarks
Enter system view	system-view	—
		Required
Enable IGMP Snooping	igmp-snooping enable	By default, IGMP Snooping is
		disabled.
Enter VLAN view	vlan vlan-id	—
Enable IGMP Snooping	igmp-snooping enable	Required.
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