【正文】 FilterModeChange Record for that group. As with CurrentState Records, routers must act upon these records and possibly change their own state to reflect the new desired membership state of the work. Alberto Ornaghi 2022 39 IGMP v3 The protocol (for multicast routers) Action on Reception of Queries ? Timer Updates ? Querier Election IGMPv3 elects a single querier per sub using the same querier election mechanism as IGMPv2, namely by IP address. If a router receives an older version query, it MUST use the oldest version of IGMP on the work. Alberto Ornaghi 2022 40 IGMP v3 Interoperation with older version IGMP version 3 hosts and routers interoperate with hosts and routers that have not yet been upgraded to IGMPv3. This patibility is maintained by hosts and routers taking appropriate actions depending on the versions of IGMP operating on hosts and routers within a work. The IGMP version of a Membership Query message is determined as follows: IGMPv1 Query: length = 8 octets AND Max Resp Code field is zero IGMPv2 Query: length = 8 octets AND Max Resp Code field is nonzero IGMPv3 Query: length = 12 octets Alberto Ornaghi 2022 41 IGMP v3 Interoperation with older version Group Member Behavior In the Presence of Older Version Queriers In order to be patible with older version routers, IGMPv3 hosts MUST operate in version 1 and version 2 patibility modes. IGMPv3 hosts MUST keep state per local interface regarding the patibility mode of each attached work. A host39。 a multicast router is not required to keep track of the interests of each individual neighboring system. IGMPv3 is backward patible with previous versions of the IGMP protocol. In order to remain backward patible with older IGMP systems, IGMPv3 multicast routers MUST also implement versions 1 and 2 of the protocol. Alberto Ornaghi 2022 33 IGMP v3 The protocol (for multicast routers) Conditions for IGMP Queries ? Periodic request for membership Multicast routers send General Queries periodically to request group membership information from an attached work. 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。Alberto Ornaghi 2022 1 IGMP v3 Inter Group Management Protocol, Version 3 References : Alberto Ornaghi 2022 2 Abstract This document specifies Version 3 of the Inter Group Management Protocol, IGMPv3. IGMP is the protocol used by IPv4 systems to report their IP multicast group memberships to neighboring multicast routers. Version 3 of IGMP adds support for source filtering, that is, the ability for a system to report interest in receiving packets *only* from specific source addresses, or from *all but* specific source addresses, sent to a particular multicast address. That information may be used by multicast routing protocols to avoid delivering multicast packets from specific sources to works where there are no interested receivers. Alberto Ornaghi 2022 3 Table of contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. IGMP v1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. IGMP v2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4. IGMP v3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5. The API for Requesting IP Multicast Reception . . . . . . . 11 6. Message Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 7. Desc