CHAPTER 7. MultiCast Protocols136 © SAMSUNG Electronics Co., Ltd.Internet Group Management Protocol (IGMP)Internet Group Management Protocol(IGMP) is enabled on hosts and routersthat want to receive multicast traffic. IGMP informs locally-attached routers oftheir multicast group memberships. Hosts inform routers of the groups ofwhich they are members by multicasting IGMP Group Membership Reports.When multicast routers listen for these reports, they can exchange groupmembership information with other multicast routers. This reporting systemallows distribution trees to be formed to deliver multicast datagrams.The original version of IGMP was defined in RFC 1112, Host Extensions forIP Multicasting. Extensions to IGMP, known as IGMP version 2.IGMPv2 improves performance and supports the following message types:1. IGMP Query: IGMP Query is sent by the router to know which groupshave members on the attached network.2. IGMP Reports: IGMP reports are sent as a response to the query by hoststo announce their group membership. Reports can be sent ‘unsolicited’when the hosts come up.3. IGMP Leaves: IGMP Leaves are sent by the host when it relinquishesmembership of a group.IGMP Version 3 is not supported in this release.
