Operation Manual – MulticastH3C S5500-EI Series Ethernet Switches Chapter 6 IGMP Configuration6-4II. “Leave group” mechanismIn IGMPv1, when a host leaves a multicast group, it does not send any notification tothe multicast router. The multicast router relies on host response timeout to knowwhether a group no longer has members. This adds to the leave latency.In IGMPv2, on the other hand, when a host leaves a multicast group:1) This host sends a Leave Group message (often referred to as leave message) toall routers (the destination address is 224.0.0.2) on the local subnet.2) Upon receiving the leave message, the querier sends a configurable number ofgroup-specific queries to the group being left. The destination address field andgroup address field of the message are both filled with the address of the multicastgroup being queried.3) One of the remaining members, if any on the subnet, of the group being queriedshould send a membership report within the maximum response time set in thequery messages.4) If the querier receives a membership report for the group within the maximumresponse time, it will maintain the memberships of the group; otherwise, thequerier will assume that no hosts on the subnet are still interested in multicasttraffic to that group and will stop maintaining the memberships of the group.6.1.4 Enhancements in IGMPv3Note:The support for the Exclude mode varies with device models.Built upon and being compatible with IGMPv1 and IGMPv2, IGMPv3 provides hostswith enhanced control capabilities and provides enhancements of query and reportmessages.I. Enhancements in control capability of hostsIGMPv3 has introduced source filtering modes (Include and Exclude), so that a host notonly can join a designated multicast group but also can specify to receive or rejectmulticast data from a designated multicast source. When a host joins a multicast group:z If it needs to receive multicast data from specific sources like S1, S2, …, it sends areport with the Filter-Mode denoted as “Include Sources (S1, S2, ……).z If it needs to reject multicast data from specific sources like S1, S2, …, it sends areport with the Filter-Mode denoted as “Exclude Sources (S1, S2, ……).As shown in Figure 6-2, the network comprises two multicast sources, Source 1 (S1)and Source 2 (S2), both of which can send multicast data to multicast group G. Host B
