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z To prevent bursting traffic in the network or performance deterioration of the device caused by
excessive multicast groups, you can set the maximum number of multicast groups that the switch
should process.
z When the number of multicast groups exceeds the configured limit, the switch removes its
multicast forwarding entries starting from the oldest one. In this case, the multicast packets for the
removed multicast group(s) will be flooded in the VLAN as unknown multicast packets. As a result,
non-member ports can receive multicast packets within a period of time. To avoid this from
happening, enable the function of dropping unknown multicast packets.
Configuring IGMP Snooping Querier
In an IP multicast network running IGMP, one dedicated multicast device is responsible for sending
IGMP general queries, and this router or Layer 3 switch is called the IGMP querier.
However, a Layer 2 multicast switch does not support IGMP, and therefore cannot send general queries
by default. By enabling IGMP Snooping querier on a Layer 2 switch in a VLAN where multicast traffic
needs to be Layer-2 switched only and no multicast routers are present, the Layer 2 switch will act as a
querier to send IGMP general queries, thus allowing multicast forwarding entries to be established and
maintained at the data link layer.
Upon receiving an IGMP query with the source IP address 0.0.0.0 on a port, the switch does not enlist
that port as a dynamic router port. This may prevent multicast forwarding entries from being correctly
created at the data link layer and cause multicast traffic forwarding failure in the end. When a Layer 2
device acts as an IGMP-Snooping querier, to avoid the aforesaid problem, configure a non-all-zero IP
address as the source IP address of IGMP queries.
IGMP Snooping querier related configurations include:
z Enabling IGMP Snooping querier,
z Configuring the IGMP query interval, and
z Configuring the source address to be carried in IGMP general and group specific queries.
Enabling IGMP Snooping querier
Follow these steps to enable IGMP Snooping querier:
To do... Use the command... Remarks
Enter system view
system-view
—
Enable IGMP Snooping
igmp-snooping enable
Required
By default, IGMP Snooping is
disabled.
Enter VLAN view
vlan vlan-id
—
Enable IGMP Snooping
igmp-snooping enable
Required
By default, IGMP Snooping is
disabled.