2-9
Operation Command Remarks
Limit the number of multicast
groups on a port
igmp-snooping group-limit limit
[ vlan vlan-list [ overflow-replace ] ]
Required
The system default for
Switch 4200G series is
256.
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 Querier
In an IP multicast network running IGMP, a multicast router or Layer 3 multicast switch is responsible for
sending IGMP general queries, so that all Layer 3 multicast devices can establish and maintain
multicast forwarding entries, thus to forward multicast traffic correctly at the network layer. This router or
Layer 3 switch is called IGMP querier.
However, a Layer 2 multicast switch does not support IGMP, and therefore cannot send general queries
by default. By enabling IGMP Snooping 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 the IGMP
Snooping querier to send IGMP general queries, thus allowing multicast forwarding entries to be
established and maintained at the data link layer.
You can also configure the source address, maximum response time and interval of general queries to
be sent from the IGMP Snooping querier.
Table 2-11 Configure IGMP Snooping querier
Operation 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.
Enable IGMP Snooping querier
igmp-snooping querier
Required
By default, IGMP Snooping
querier is disabled.
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