【正文】 desired or not desired, depending on the filter mode. Alberto Ornaghi 2022 13 IGMP v3 API patibility Previous versions of IGMP did not support source filters and had a simpler API consisting of Join and Leave operations to enable and disable reception of a given multicast address (from *all* sources) on a given interface. The Join operation is equivalent to IPMulticastListen ( socket, interface, multicastaddress, EXCLUDE, {} ) and the Leave operation is equivalent to: IPMulticastListen ( socket, interface, multicastaddress, INCLUDE, {} ) where {} is an empty source list. Alberto Ornaghi 2022 14 IGMP v3 API example For example, suppose one application or process invokes the following operation on socket s1: IPMulticastListen ( s1, i, m, INCLUDE, {a, b, c} ) requesting reception on interface i of packets sent to multicast address m, *only* if they e from source a, b, or c. Suppose another application or process invokes the following operation on socket s2: IPMulticastListen ( s2, i, m, INCLUDE, {b, c, d} ) Thus, in this example, the reception state of interface i for multicast address m has filter mode INCLUDE and source list {a, b, c, d}. Alberto Ornaghi 2022 15 IGMP v3 Message format IGMP messages are encapsulated in IPv4 datagrams, with an IP protocol number of 2. Every IGMP message is sent with an IP TimetoLive of 1, and carries an IP Router Alert option [RFC2113] in its IP header. There are two IGMP message types of concern to the IGMPv3 protocol: Type Number (hex) Message Name 0x11 Membership Query 0x22 Version 3 Membership Report Alberto Ornaghi 2022 16 An implementation of IGMPv3 MUST also support the following three message types, for interoperation with previous versions of IGMP 0x12 Version 1 Membership Report [RFC1112] 0x16 Version 2 Membership Report [RFC2236] 0x17 Version 2 Leave Group [RFC2236] IGMP v3 Message format Alberto Ornaghi 2022 17 IGMP v3 Message format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +++++++++++++++++++++++++++++++++ | Type = 0x11 | Max Resp Code | Checksum | +++++++++++++++++++++++++++++++++ | Group Address | +++++++++++++++++++++++++++++++++ | Resv |S| QRV | IC | Number of Sources (N) | +++++++++++++++++++++++++++++++++ | Source Address [1] | + + | Source Address [2] | + . + . . . . . . + + | Source Address [N] | +++++++++++++++++++++++++++++++++ Membership Query Message Alberto Ornaghi 2022 18 IGMP v3 Message format The Max Resp Code field specifies the maximum time allowed before sending a responding report. Allow IGMPv3 routers to tune the leave latency“. The Group Address field is set to zero when sending a General Query, and set to the IP multicast address being queried when sending a GroupSpecific Query or GroupandSourceSpecific Query The Querier39。s Query Interval Code field specifies the [Query Interval] used by the querier. The Number of Sources (N) field specifies how many source addresses are present in the Query. The Source Address [i] fields are a vector of n IP unicast addresses, where n is the value in the Number of Sources (N) field. Membership Query Message Alberto Ornaghi 2022 19 IGMP v3 Message format There are three variants of the Query message: 1. A General Query” 2. A GroupSpecific Query” 3. A GroupandSourceSpecific Query” Membership Query Message In IGMPv3, General Queries are sent with an IP destination address of , the allsystems multicast address. GroupSpecific and GroupandSourceSpecific Queries are sent with an IP destination address equal to the multicast address of interest. Alberto Ornaghi 2022 20 IGMP v3 Message format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +++++++++++++++++++++++++++++++++ | Type = 0x22 | Reserved | Checksum | +++++++++++++++++++++++++++++++++ | Reserved | Number of Group Records (M) | +++++++++++++++++++++++++++++++++ | | . Group Record [1] . | | +++++++++++++++++++++++++++++++++ | . | . . . | . | +++++++++++++++++++++++++++++++++ |