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4.6 Multicast at the Network Layer

4.6 Multicast at the Network Layer. 4.6.1 Introduction: The Internet multicast abstraction and multicast groups 4.6.2 The IGMP Protocol 4.6.3 Multicast Routing: the general case 4.6.4 Multicast Routing in the Internet. Multicast: one sender to many receivers

shelley-whitney
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4.6 Multicast at the Network Layer

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  1. 4.6 Multicast at the Network Layer 4.6.1 Introduction: The Internet multicast abstraction and multicast groups4.6.2 The IGMP Protocol4.6.3 Multicast Routing: the general case4.6.4 Multicast Routing in the Internet

  2. Multicast: one sender to many receivers analogy: one teacher to many students Question: how to achieve multicast Multicast: one sender to many receivers

  3. Internet Multicast Service Model multicast group concept: • hosts send IP datagram pkts to multicast group • hosts that have “joined” that multicast group will receive pkts sent to that group

  4. Multicast groups • host group semantics: • anyone can “join” (receive) multicast group • anyone can send to multicast gorup • no network layer identification to hosts of members • session/application-level mechanisms needed for membership identification, privacy • needed: infrastructure to deliver mcast-addressed packets to all hosts that have joined that multicast group

  5. Internet Multicast Addressing • class D Internet addresses reserved for multicast: • indirection: mcast address does not name a destination, but host group to receive packet packet addr: 226.17.30.197

  6. Joining a mcast group: a two-step process • local: host informs local mcast router of desire to join group: IGMP • wide area: local router interacts with other routers to receive mcast packet flow • many protocols (e.g., DVMRP, MOSPF, PIM)

  7. IGMP: Internet Group Management Protocol • host: sends IGMP report when application joins mcast group • IP_ADD_MEMBERSHIP socket option • host need not explicitly “unjoin” group when leaving • router: sends IGMP query at regular intervals • host belonging to a mcast group must reply to query

  8. IGMP version 1 router: Host Membership Query msg broadcast on LAN to all hosts host: Host Membership Report msg to indicate group membership randomized delay before responding implicit leave via no reply to Query RFC 1112 IGMP v2: additions include group-specific Query Leave Group msg last host replying to Query can send explicit Leave Group msg router performs group-specific query to see if any hosts left in group RFC 2236 IGMP v3: under development as Internet draft IGMP

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