4.9 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.
Table 4-24. IGMP Snooping screen options.
Parameter Description
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.
IGMP snooping mode selection
The switch supports three kinds of IGMP Snooping status,
including “Passive”, “Active” and “Disable”.
Disable:
Set “Disable” mode to disable IGMP Snooping function.
Default: Disable
Active:
In Active mode, IGMP snooping switch will periodically issue the
Membership Query message to all hosts attached to it and gather
the Membership report message to update the database of the
Multicast table. By the way, this also reduces the unnecessary
multicast traffic.
Passive:
In Passive Snooping mode, the IGMP snooping will not periodically
poll the hosts in the groups. The switch will send a Membership
Query message to all hosts only when it has received a
Membership Query message from a router.
CHAPTER 4: Web-Based Management
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