Operation Manual – Multicast ProtocolH3C S3610&S5510 Series Ethernet Switches Chapter 5 IGMP Configuration5-11To do... Use the command... DescriptionConfigure the interface todiscard any IGMPmessage that does notcarry the Router-Alertoptionigmprequire-router-alertOptionalBy default, the devicedoes not check theRouter-Alert option.Enable the insertion of theRouter-Alert option intoIGMP messagesigmp send-router-alertOptionalBy default, IGMPmessages carry theRouter-Alert option.5.4.3 Configuring IGMP Query and Response ParametersThe IGMP querier periodically sends IGMP general queries at the “IGMP queryinterval” to determine whether any multicast group member exists on the network. Youcan tune the IGMP general query interval based on actual condition of the network.On startup, the IGMP querier sends “startup query count” IGMP general queries at the“startup query interval”, which is 1/0/5 of the “IGMP query interval”. Upon receiving anIGMP leave message, the IGMP querier sends “last member query count” IGMPgroup-specific queries at the “IGMP last member query interval”. Both startup querycount and last member query count are set to the IGMP querier robustness variable.IGMP is robust to “robustness variable minus 1” packet losses on a network. Therefore,a greater value of the robustness variable makes the IGMP querier “more robust”, butresults in a longer multicast group timeout time.Upon receiving an IGMP query (general query or group-specific query), a host starts adelay timer for each multicast group it has joined. This timer is initialized to a randomvalue in the range of 0 to the maximum response time, which is derived from the MaxResponse Time field in the IGMP query. When the timer value comes down to 0, thehost sends an IGMP report to the corresponding multicast group.An appropriate setting of the maximum response time for IGMP queries allows hosts torespond to queries quickly and avoids bursts of IGMP traffic on the network caused byreports simultaneously sent by a large number of hosts when the corresponding timersexpires simultaneously.z For IGMP general queries, you can configure the maximum response time to filltheir Max Response time field.z For IGMP group-specific queries, you can configure the IGMP last member queryinterval to fill their Max Response time field. Namely, for IGMP group-specificqueries, the maximum response time equals the IGMP last member query interval.When multiple multicast routers exist on the same subnet, the IGMP querier isresponsible for sending IGMP queries. If a non-querier router receives no IGMP queryfrom the querier within the “other querier present interval”, it will assume the querier to
