【正文】 These queries are used to build and refresh the group membership state of systems on attached works. Systems respond to these queries by reporting their group membership state (and their desired set of sources) with CurrentState Group Records in IGMPv3 Membership Reports. router IGMP Request Alberto Ornaghi 2022 34 IGMP v3 The protocol (for multicast routers) ? Group Specific Query To enable all systems on a work to respond to changes in group membership, multicast routers send specific queries. A Group Specific Query is sent to verify there are no systems that desire reception of the specified group or to rebuild the desired reception state for a particular group. GroupSpecific Queries are sent when a router receives a StateChange record indicating a system is leaving a group. router Multicast interested hosts Other hosts A A B IGMP leave A IGMP Group specific Alberto Ornaghi 2022 35 IGMP v3 The protocol (for multicast routers) ? Group and Source Specific Query A GroupandSource Specific Query is used to verify there are no systems on a work which desire to receive traffic from a set of sources. GroupandSource Specific Queries list sources for a particular group which have been requested to no longer be forwarded. This query is sent by a multicast router to learn if any systems desire reception of packets to the specified group address from the specified source addresses. Alberto Ornaghi 2022 36 IGMP v3 The protocol (for multicast routers) IGMP State Maintained by Multicast Routers Multicast routers implementing IGMPv3 keep state per group per attached work. This group state consists of: ? a filtermode, ? a list of sources, ? and various timers. For each attached work running IGMP, a multicast router records the desired reception state for that work. That state conceptually consists of a set of records of the form: (multicast address, group timer, filtermode, (source records)) Alberto Ornaghi 2022 37 IGMP v3 The protocol (for multicast routers) Definition of Router FilterMode To reduce internal state, IGMPv3 routers keep a filtermode per group per attached work. This filtermode is used to condense the total desired reception state of a group to a minimum set such that all systems39。s patibility mode is determined from the Host Compatibility Mode variable which can be in one of three states: IGMPv1, IGMPv2 or IGMPv3. This variable is kept per interface and is dependent on the version of General Queries heard on that interface as well as the Older Version Querier Present timers for the interface. Alberto Ornaghi 2022 42 IGMP v3 Interoperation with older version Multicast Router Behavior In the Presence of Older Version Queriers IGMPv3 routers may be placed on a work where at least one router on the work has not yet been upgraded to IGMPv3. If any older versions of IGMP are present on routers, the querier MUST use the lowest version of IGMP present on the work. When in IGMPv1 mode, routers MUST send Periodic Queries with a Max Resp Code of 0 and truncated at the Group Address field (. 8 bytes long), and MUST ignore Leave Group messages. When in IGMPv2 mode, routers MUST send Periodic Queries truncated at the Group Address field (. 8 bytes long) Alberto Ornaghi 2022 43 IGMP v3 Interoperation with older version Multicast Router Behavior In the Presence of Older Version Group Members IGMPv3 routers may be placed on a work where there are hosts that have not yet been upgraded to IGMPv3. In order to be patible with older version hosts, IGMPv3 routers MUST operate in version 1 and version 2 patibility modes. In order to switch gracefully between versions of IGMP, routers keep an IGMPv1 Host Present timer and an IGMPv2 Host Present timer per group record. Alberto Ornaghi 2022 44 IGMP v3 Interoperation with older version Multicast Router Behavior When Group Compatibility Mode is IGMPv3, a router acts using the IGMPv3 protocol for that group. When Group Compatibility Mode is IGMPv2, a router acts in IGMPv2 patibility mode, treating all IGMPv3 messages mentioning a group as membership in that group, except IS_INC( {} ) and TO_INC( {} ), which are treated as IGMPv2 Leave messages. ALLOW() and BLOCK() messages are ignored. When Group Compatibility Mode is IGMPv1, a router acts in IGMPv1 patibility mode, treating IGMPv3 messages as above but adittionally ignoring IGMPv2 Leave messages. Alberto Ornaghi 2022 45 IGMP v3 Timers Most of these timers are configurable. If nondefault settings are used, they MUST be consistent among all systems. Robustness Variable The Robustness Variable allows tuning for the expected packet loss on a work. If a work is expected to be lossy, the Robustness Variable may be increased. IGMP is robust to (Robustness Variable 1) packet losses. The Robustness Variable MUST NOT be zero, and SHOULD NOT be one. Default: 2 Query Interval The Query Interval is the interval between General Queries sent by the Querier. Default: 125 seconds. Alberto Ornaghi 2022 46 IGMP v3 Timers Query Response Interval The Max Response Time used to calculate the Max Resp Code inserted into the periodic General Queries. Default: 100 (10 seconds) The number of seconds represented by the [Query Response Interval] must be less than the [Query Interval]. Group Membership Interval The Group Membership Interval is the amount of time that must pass before a multicast router decides there are no more members of a group or a particular source on a work. This value MUST be ((the Robustness Variable) * (the Query Interval)) + (one Query Response Interval). Alberto Ornaghi 2