The IGS switch is configured to send IGMP general queries on all of the nonrouter ports when a spanning tree topology change occurs in the network. If the spanning tree mode is RSTP, IGMP general queries are sent on all of the nonrouter ports that are the VLANs member ports present in the switch. If the spanning tree mode is MSTP, IGMP general queries are sent on all of the nonrouter ports of the VLAN that are mapped for the MSTP instance. The IGMP general query transmission option is disabled by default. Before you can configure IGS features, you must configure your network environment, as described in Topology Example.