620 CHAPTER 46: IGMP CONFIGURATIONn ■ Before you can configure an interface of a PIM-SM device as a static memberof a multicast group, if the interface is PIM-SM enabled, it must be a PIM-SMDR; if this interface is IGMP enabled but not PIM-SM enabled, it must be anIGMP querier.■ As a static member of a multicast group, an interface does not respond to thequeries from the IGMP querier, nor does it send an unsolicited IGMPmembership report or an IGMP leave group message when it joins or leaves amulticast group. In other words, the interface will not become a real memberof the multicast group.Configuring a MulticastGroup FilterYou can configure a multicast group filter in IGMP Snooping. For details, see“Configuring a Multicast Group Filter” on page 566.Adjusting IGMPPerformancen For the configuration tasks described in this section■ Configurations performed in IGMP view are effective on all interfaces, whileconfigurations performed in interface view are effective on the currentinterface only.■ If the same feature is configured in both IGMP view and interface view, theconfiguration performed in interface view is given priority, regardless of theconfiguration sequence.ConfigurationPrerequisitesBefore adjusting IGMP performance, complete the following tasks:■ Configure any unicast routing protocol so that all devices in the domain areinteroperable at the network layer.■ Configure basic functions of IGMPBefore adjusting IGMP performance, prepare the following data:■ IGMP general query interval■ IGMP querier’s robustness variable■ Maximum response time for IGMP general queries■ IGMP last-member query interval■ Other querier present intervalConfiguring IGMPMessage OptionsAs IGMPv2 and IGMPv3 involve group-specific and group-and-source-specificqueries, and multicast groups change dynamically, a device cannot join allmulticast groups. Therefore, when receiving a multicast packet but unable tolocate the outgoing interface for the destination multicast group, an IGMP routerneeds to leverage the Router-Alert option to pass the multicast packet to theupper-layer protocol for processing. For details about the Router-Alert option, referto RFC 2113.An IGMP message is processed differently depending whether it carries theRouter-Alert option in the IP header:
