3com WX3000 Manuel D’Utilisation

 

2-9 

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

Enter system view 

— 

Enter Ethernet port view 

interface interface-type 
interface-number 

— 

Limit the number of multicast 
groups on a port 

igmp-snooping group-limit limit 
[ vlan vlan-list [ overflow-replace ] ]

Required 

The system default for 
the device is 256. 

 

z 

To 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.  

z 

When 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.  

 

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: 

Enter system view 

— 

Enable IGMP Snooping 

Required 

By default, IGMP Snooping is 
disabled. 

Enter VLAN view 

vlan vlan-id 

— 

Enable IGMP Snooping 

Required.