2-3Aging timers for dynamic ports in IGMP Snooping and related messages and actionsTable 2-1 Aging timers for dynamic ports in IGMP Snooping and related messages and actionsTimer Description Message beforeexpiry Action after expiryDynamic router portaging timerFor each dynamicrouter port, the switchsets a timer initializedto the dynamic routerport aging time.IGMP general query ofwhich the sourceaddress is not 0.0.0.0or PIM helloThe switch removesthis port from its routerport list.Dynamic member portaging timerWhen a portdynamically joins amulticast group, theswitch sets a timer forthe port, which isinitialized to thedynamic member portaging time.IGMP membershipreportThe switch removesthis port from theIGMP Snoopingforwarding table.The port aging mechanism of IGMP Snooping works only for dynamic ports; a static port will never ageout.How IGMP Snooping WorksA switch running IGMP Snooping performs different actions when it receives different IGMP messages,as follows:The description about adding or deleting a port in this section is only for a dynamic port. Static portscan be added or deleted only through the corresponding configurations. For details, see ConfiguringStatic Ports.When receiving a general queryThe IGMP querier periodically sends IGMP general queries to all hosts and routers (224.0.0.1) on thelocal subnet to find out whether active multicast group members exist on the subnet.Upon receiving an IGMP general query, the switch forwards it through all ports in the VLAN except thereceiving port and performs the following to the receiving port:z If the receiving port is a dynamic router port existing in its router port list, the switch resets theaging timer of this dynamic router port.z If the receiving port is not a dynamic router port existing in its router port list, the switch adds it intoits router port list and sets an aging timer for this dynamic router port.
