21418 – IGMPMulticast traffic on a networknternet Group Management Protocol (IGMP) is defined in RFC 1112 as the standard for IPmulticasting in the Internet. It is used to establish host memberships in particular multicastgroups on a single network. The mechanisms of the protocol allows a host to inform itslocal router, using Host Membership Reports that it wants to receive messages addressed toa specific multicast group. All hosts conforming to level 2 of the IP multicastingspecification require IGMP.IGTdMP concepts8he Magnum 6K family of switches supports IGMP L2 standards asefined by RFC 1112. IGMP is disabled by default and needs to beenabled on the Magnum 6K family of switches. IP multicasting is definedas the transmission of an IP datagram to a "host group", a set of zero or more hosts identified bya single IP destination address. A multicast datagram is delivered to all members of its destinationhost group with the same "best-efforts" reliability as regular unicast IP datagram, i.e. the datagramis not guaranteed to arrive at all members of the destination group or in the same order relative toother datagram.The membership of a host group is dynamic; that is, hosts may join and leave groups at any time.There is no restriction on the location or number of members in a host group, but membership ina group may be restricted to only those hosts possessing a private access key. A host may be amember of more than one group at a time. A host need not be a member of a group to senddatagram to it.A host group may be permanent or transient. A permanent group has a well-known,administratively assigned IP address. It is the address and not the membership of the group that ispermanent; at any time a permanent group may have any number of members, even zero. Atransient group on the other hand is assigned an address dynamically when the group is created, atthe request of a host. A transient group ceases to exist, and its address becomes eligible forreassignment, when its membership drops to zero.8 Most of the concepts are extracted from RFC 1112 and it is recommended that RFC 1112 be read and understood carefully ifIGMP is used or planned for the network.Chapter18Ij
