Netis ST3326(ST-3302) [95/118] Igmp report suppression

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The router sends periodic multicast general queries and the switch forwards these queries through all
ports in the VLAN. Interested hosts respond to the queries. If at least one host in the VLAN wishes to
receive multicast traffic, the router continues forwarding the multicast traffic to the VLAN. The switch
forwards multicast group traffic to only those hosts listed in the forwarding table for that Layer 2
multicast group.
When hosts want to leave a multicast group, they can either silently leave, or they can send a leave
message. When the switch receives a leave message from a host, it sends out a MAC-based general
query to determine if any other devices connected to that interface are interested in traffic for the
specific multicast group. The switch then updates the forwarding table for that MAC group so that
only those hosts interested in receiving multicast traffic for the group are listed in the forwarding
table. If the router receives no reports from a VLAN, it removes the group for the VLAN from its IGMP
cache.
Immediate-Leave Processing
Immediate Leave is only supported with IGMP version 2 hosts.
The switch uses IGMP snooping Immediate-Leave processing to remove from the forwarding table an
interface that sends a leave message without the switch sending MAC-based general queries to the
interface. The VLAN interface is pruned from the multicast tree for the multicast group specified in
the original leave message. Immediate-Leave processing ensures optimal bandwidth management for
all hosts on a switched network, even when multiple multicast groups are simultaneously in use.
IGMP Report Suppression
The switch uses IGMP report suppression to forward only one IGMP report per multicast router query
to multicast devices. When IGMP router suppression is enabled (the default), the switch sends the
first IGMP report from all hosts for a group to all the multicast routers. The switch does not send the
remaining IGMP reports for the group to the multicast routers. This feature prevents duplicate
reports from being sent to the multicast devices.
If the multicast router query includes requests only for IGMPv1 and IGMPv2 reports, the switch
forwards only the first IGMPv1 or IGMPv2 report from all hosts for a group to all the multicast
routers.
If the multicast router query also includes requests for IGMPv3 reports, the switch forwards all
IGMPv1,IGMPv2, and IGMPv3 reports for a group to the multicast devices.
If you disable IGMP report suppression, all IGMP reports are forwarded to the multicast routers.

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