414 | Internet Group Management Protocolw w w . d e l l . c o m | s u p p o r t . d e l l . c o m • When enabled, IGMP snooping Querier starts after one query interval in case no IGMP general query(with IP SA lower than its VLAN IP address) is received on any of its VLAN members.Adjusting the Last Member Query IntervalWhen the querier receives a leave message from a receiver, it sends a group-specific query out of the portsspecified in the forwarding table. If no response is received, it sends another. The amount of time that thequerier waits to receive a response to the initial query before sending a second one is the Last MemberQuery Interval (LMQI). The switch waits one LMQI after the second query before removing thegroup-port entry from the forwarding table.Adjust the Last Member Query Interval using the command ip igmp snooping last-member-query-intervalfrom INTERFACE VLAN mode.Fast Convergence after MSTP Topology ChangesWhen a port transitions to the Forwarding state as a result of an STP or MSTP topology change, FTOSsends a general query out of all ports except the multicast router ports. The host sends a response to thegeneral query and the forwarding database is updated without having to wait for the query interval toexpire.When an IGMP snooping switch is not acting as a Querier it sends out the general query, in response to theMSTP triggered link-layer topology change, with the source IP address of 0.0.0.0 to avoid triggeringQuerier election.Designating a Multicast Router InterfaceYou can designate an interface as a multicast router interface with the command ip igmp snoopingmrouter interface. FTOS also has the capability of listening in on the incoming IGMP General Queriesand designate those interfaces as the multicast router interface when the frames have a non-zero IP sourceaddress. All IGMP control packets and IP multicast data traffic originating from receivers is forwarded tomulticast router interfaces.
