24-Port Managed Gigabit Switch
3.8.2 IGMP Snooping Working Mechanism
When IGMP snooping is enabled, the multicast router sends out
periodic IGMP general queries to all VLANs. The switch responds
to the router queriers with only one join request per MAC multicast
group, and the switch creates one entry per VLAN in the Layer 2
forwarding table for each MAC group from which it receives an
IGMP join request. All hosts interested in this multicast traffic send
join requests and are added to thef forwarding table entry.
When the switch receives IGMP Leave Group message from a host,
it removes the host port from the table entry. After it relays the IGMP
queries from the multicast router, it deletes entries periodically if it
does receive any IGMP membership reports from the multicast
clients.
1. Joining a Multicast Group
When a host connected to the Switch wants to join an IP multicast
group, it sends an IGMP join message (IGMP membership report),
specifying the IP multicast group it wants to join. When the Switch
receives this message, it adds the port to the IP multicast group port
address entry in the forwarding table.
2. Leaving a Multicast Group
The router sends periodic IP multicast general queries, and the
switch responds to these queries with one join responsed per MAC
multicast group. As long as at lest one host in the VLAN needs
multicast traffic, the Switch responds to the reouter queries, and
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