LevelOne GSW-2690 Manuale Utente

The function, IGMP Snooping, is used to establish the multicast groups to 

forward the multicast packet to the member ports, and, in nature, avoids wasting the 
bandwidth while IP multicast packets are running over the network. This is because 
a switch that does not support IGMP or IGMP Snooping can not tell the multicast 
packet from the broadcast packet, so it can only treat them all as the broadcast 
packet. Without IGMP Snooping, the multicast packet forwarding function is plain 
and nothing is different from broadcast packet. 

A switch supported IGMP Snooping with the functions of query, report and 

leave, a type of packet exchanged between IP Multicast Router/Switch and IP 
Multicast Host, can update the information of the Multicast table when a member 
(port) joins or leaves an IP Multicast Destination Address. With this function, once a 
switch receives an IP multicast packet, it will forward the packet to the members 
who joined in a specified IP multicast group before. 

 

Fig. 3-17

 

 

IGMP Snooping  

IGMP is used to snoop the status of IP multicast groups and display its 
associated information in both tagged VLAN and non-tagged VLAN networks.  
Enabling IGMP with either passive or active mode, you can monitor the IGMP 
snooping information, which contains the multicast member list with the 
multicast groups, VID and member port.