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4.6 Multicast at the Network Layer

Explore the concept of Internet multicast operations, including IGMP protocol, multicast routing in the Internet, and multicast addressing. Learn how hosts join multicast groups and how routers manage multicast traffic efficiently.

robertcook
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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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