Dell S4048T, Configuration Manual

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IGMP Protocol Overview
IGMP has three versions. Version 3 obsoletes and is backwards-compatible with version 2; version 2 obsoletes
version 1.
IGMP Version 2
IGMP version 2 improves on version 1 by specifying IGMP Leave messages, which allows hosts to notify
routers that they no longer care about traffic for a particular group.
Leave messages reduce the amount of time that the router takes to stop forwarding traffic for a group to a
subnet (leave latency) after the last host leaves the group. In version 1 hosts quietly leave groups, and the
router waits for a query response timer several times the value of the query interval to expire before it stops
forwarding traffic.
To receive multicast traffic from a particular source, a host must join the multicast group to which the source
is sending traffic. A host that is a member of a group is called a receiver. A host may join many groups, and
may join or leave any group at any time. A host joins and leaves a multicast group by sending an IGMP
message to its IGMP Querier. The querier is the router that surveys a subnet for multicast receivers and
processes survey responses to populate the multicast routing table.
IGMP messages are encapsulated in IP packets, as shown in the following illustration.
Figure 47. IGMP Messages in IP Packets
Internet Group Management Protocol (IGMP) 426