2-9Operation Command RemarksConfigure the maximumnumber of multicast groupsallowed on the portigmp-snooping group-limitlimit [ vlan vlan-list[ overflow-replace ] ]RequiredThe system default is 512.z To prevent bursting traffic in the network or performance deterioration of the device caused byexcessive multicast groups, you can set the maximum number of multicast groups that the switchshould process.z When the number of multicast groups exceeds the configured limit, the switch removes itsmulticast forwarding entries starting from the oldest one. In this case, the multicast packets for theremoved 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 fromhappening, enable the function of dropping unknown multicast packets.Configuring IGMP Snooping QuerierIn an IP multicast network running IGMP, one dedicated multicast device is responsible for sendingIGMP 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 queriesby default. By enabling IGMP Snooping querier on a Layer 2 switch in a VLAN where multicast trafficneeds to be Layer-2 switched only and no multicast routers are present, the Layer 2 switch will act as aquerier to send IGMP general queries, thus allowing multicast forwarding entries to be established andmaintained 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 enlistthat port as a dynamic router port. This may prevent multicast forwarding entries from being correctlycreated at the data link layer and cause multicast traffic forwarding failure in the end. When a Layer 2device acts as an IGMP-Snooping querier, to avoid the aforesaid problem, configure a non-all-zero IPaddress 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, andz Configuring the source address to be carried in IGMP general and group specific queries.Enabling IGMP Snooping querierFollow these steps to enable IGMP Snooping querier:Operation Command RemarksEnter system view system-view —Enable IGMP Snooping igmp-snooping enableRequiredBy default, IGMP Snooping isdisabled.Enter VLAN view vlan vlan-id —
