Configuring Layer 2 Multicast IGMP Snooping Configuration
Configuration Guide
219
Figure 2-2 Configure IGMP Snooping for VLAN
Follow these steps to configure IGMP Snooping for a specific VLAN:
1) Enable IGMP Snooping for the VLAN, and configure the corresponding parameters.
VLAN ID Displays the VLAN ID.
IGMP Snooping
Status
Enable or disable IGMP Snooping for the VLAN.
Fast Leave Enable or disable Fast Leave for the VLAN. IGMPv1 does not support Fast Leave.
Without Fast Leave, after a receiver sends an IGMP leave message to leave a
multicast group, the switch will forward the leave message to the Layer 3 device
(the querier).
From the point of view of the querier, the port connecting to the switch is a
member port of the corresponding multicast group. After receiving the leave
message from the switch, the querier will send out a configured number (Last
Member Query Count) of group-specific queries on that port with a configured
interval (Last Member Query Interval), and wait for IGMP group membership
reports. If there are other receivers connecting to the switch, they will response
to the queries before the Last Member Query Interval expires. If no reports are
received after the response time of the last query expires, the querier will remove
the port from the forwarding list of the corresponding multicast group.
That is, if there are other receivers connecting to the switch, the one sent leave
message have to wait until the port ages out from the switch’s forwarding list of
the corresponding multicast group (the maximum waiting time is decided by the
Member Port Aging Time).
With Fast Leave enabled on a VLAN, the switch will remove the (Multicast Group,
Port, VLAN) entry from the multicast forwarding table before forwarding the leave
message to the querier. This helps to reduce bandwidth waste since the switch
no longer sends the corresponding multicast streams to the VLAN of the port as
soon as the port receives a leave message from the VLAN.
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