Microsens MS453522M - Manual (Page 77)

MICROSENS 8 Port Gigabit Ethernet Switch User’s Manual
72
3-7. IGMP Snooping
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.
The packets will be discarded by the IGMP Snooping if the user transmits multicast
packets to the multicast group that had not been built up in advance.
Fig. 3-25
Function name:
IGMP Snooping
Function description:
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.