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IP MULTICASTING

Mario Baldiwww.baldi.info

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Underlying Concept

Packets routed from sourceto multiple destinationsKey for group communicationE.g. videoconferencing, video

broadcastingAddress

identifies a group

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Multicast Addressing

Class D addresses Begin with 111O 224.O.O.O - 239.255.255.255

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Address identifies a host groupPacket is delivered to all hosts in the

groupAnywhere in the network

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Host GroupHosts join and leave dynamicallyRecipients establish which hosts

receive a packetIn unicast it is the sourceControlling traffic reach is more

difficult

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Within an IEEE 8O2 Network

Group delivery delegatedto lower level (MAC)

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IP multicast address mapped to a MAC multicast addressO1-OO-5E-O ← 1 bit23 least significant bits of IP

address

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Interface card configured to receive that MAC multicastRecipient initiated

group join

Packets sent to the address are received by all joined hosts

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Beyond a Single NetworkRouters discover host

groups on each LANInternet Group Management

Protocol (IGMP)Routers announce host

groups to othersMulticast routing protocols

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Routers build a distribution tree for each host groupTo all LANs with at least a member

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State of DeploymentNot widely supportedNot fit to common traffic

control/engineering practiceMostly limited controlled environmentsE.g. video broadcasting over IP

solutions