1-15Configuring IGMP Snooping QuerierConfiguration PrerequisitesBefore configuring IGMP snooping querier, complete the following task:z Enable IGMP snooping in the VLAN.Before configuring IGMP snooping querier, prepare the following data:z IGMP general query interval,z IGMP last-member query interval,z Maximum response time to IGMP general queries,z Source address of IGMP general queries, andz Source address of IGMP group-specific queries.Enabling IGMP Snooping QuerierIn an IP multicast network running IGMP, a multicast router or Layer 3 multicast switch is responsible forsending IGMP general queries, so that all Layer 3 multicast devices can establish and maintainmulticast forwarding entries, thus to forward multicast traffic correctly at the network layer. This router orLayer 3 switch is called an IGMP querier.However, a Layer 2 multicast switch does not support IGMP, and therefore cannot send general queriesby default. By enabling IGMP snooping on a Layer 2 switch in a VLAN where multicast traffic needs tobe Layer-2 switched only and no multicast routers are present, the Layer 2 switch will act as the IGMPsnooping querier to send IGMP queries, thus allowing multicast forwarding entries to be establishedand maintained at the data link layer.Follow these steps to enable IGMP snooping querier:To do... Use the command... RemarksEnter system view system-view —Enter VLAN view vlan vlan-id —Enable IGMP snooping querier igmp-snooping querier RequiredDisabled by defaultIt is meaningless to configure an IGMP snooping querier in a multicast network running IGMP. Althoughan IGMP snooping querier does not take part in IGMP querier elections, it may affect IGMP querierelections because it sends IGMP general queries with a low source IP address.For details about IGMP querier, see IGMP Configuration of the IP Multicast Volume.Configuring IGMP Queries and ResponsesYou can tune the IGMP general query interval based on actual condition of the network.Upon receiving an IGMP query (general query or group-specific query), a host starts a timer for eachmulticast group it has joined. This timer is initialized to a random value in the range of 0 to the maximum
