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IP Multicast

IP Multicast . Stephen Li CSC457 Computer Networks University of Rochester. Outline. Introduction of multicast Model of a Host IP Implementation Intra-Domain Multicast Inter-Domain Multicast Summary . What is multicast?. One –to- many, many –to- many data transmission.

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IP Multicast

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  1. IP Multicast Stephen Li CSC457 Computer Networks University of Rochester stephen

  2. Outline • Introduction of multicast • Model of a Host IP Implementation • Intra-Domain Multicast • Inter-Domain Multicast • Summary stephen

  3. What is multicast? • One –to- many, many –to- many data transmission stephen

  4. Videoconferencing; Why multicast? LAN 1 internet router LAN 3 LAN 2 stephen

  5. Address for Multicast • Ethernet multicast address • First bit is set 1 • IP multicast address (Host group address) • Class D (from 224.0.0.0 to 239.255.255.255) • 224.0.0.0 is not assigned to any group • 224.0.0.1 is assigned to the permanent group of all IP hosts • IP multicast address is handled by IGMP (Internet Group Management Protocol) stephen

  6. Model of a Host IP Implementation Upper-Layer Protocol Modules IP Service Interface ICMP IGMP IP Module Local Network Service Interface ARP Local Network Modules (e.g Ethernet) stephen

  7. Extension to IP Service Interface • Basic functionality: • Multicast IP datagrams are sent with specified IP host group address rather than an individual IP address. • Desired functionalities: • Provides a way for upper layer to specify IP time-to-live of an outgoing multicast datagram • Provides a way for upper layer to identify which network interface is used for multicast transmission stephen

  8. Extension to Ethernet Local Network Module • Maps IP host group address to Ethernet multicast addresses • Low-order 23-bits of IP address to low-order 23-bits of Ethernet address • It is possible that multiple host group addresses are mapped to one Ethernet address since the number of significant bits of IP host group address is 28 stephen

  9. Extension to Receiver • Extension to IP service interface • An upper-layer protocol must ask the IP module to join that group • It is permissible to join the same group on more than interface • It is also permissible for more than one upper-layer protocol to request membership in the same group stephen

  10. Reverse-Path Multicast(Dense Mode) • Source broadcasts each packet on its local network • Each router that receives a packet performs a Reverse Path Forwarding(RPF) check • Leaf router checks if it knows of any group member on its attached subnets by IGMP queries • Either forward or generate a prune message • Prune message are forwarded back toward source router Leaf router source Local Network stephen

  11. Protocol Independent Multicast - Sparse Mode (PIM-SM) • RP: Rendezvous Point • Each group has a RP • RP discovery is done using a bootstrap protocol • Robustness: When the primary RP goes down, bootstrap protocol can select an alternate RP • Receivers send explicit join message to RP • Each source sends multicast data packets encapsulated in unicast packets, to RP stephen

  12. Example of PIM-SM RP Join R2 R3 R4 R5 R1 Shared tree stephen

  13. Comparison between sparse mode and dense mode • Advantage of sparse mode • Sparse mode has better scalability in terms of routing state • Sparse mode is more efficient with the explicit join message than tunnel establishment • Disadvantage of sparse mode • RP can be a single point of failure • RP can become a host spot for multicast traffic • Non-optimality may exist in the multicast tree stephen

  14. Multicast Backbone (Mbone) • Mbone is a set of multicast-capable hosts/networks connected by tunnels • Mbone has no central management • New sites can be connected anywhere (flat topology) stephen

  15. Example of MBone Multicast-capable Multicast-capable Internetwork Network2 Network1 R2 R1 10.0.0.1 Destination = 2.x Destination=10.0.01 Destination=2.x stephen

  16. Existing Problems in Intra-Domain Protocol • Scalability • Most of the routes had long prefixes, which meant that very few hosts could be represented in each routing table entry • How to apply route aggregation and hierarchical routing to mulitcast • Manageability • The utilization of tunnel may be redundant • Domain boundaries stephen

  17. Inter-Domain Multicast • MBGP: Multiprotocol Border Gateway Protocol • Review of BGP: • Autonomous System (AS) boundaries between Internet domain • ASes are commonly managed by different organizations • Entities in one AS are not trusted by entities in another AS • BGP provides policy control among ASes by advertising a complete path stephen

  18. Example of BGP 128.96 AS4 AS5 AS2 192.4.3 AS1 AS6 AS3 AS7 stephen

  19. MBGP(cont) • The basic of MBGP: • Subsequent Address Family Identifier fields are used to specify the cases: unicast, multicast, unicast/multicast • Each router only needs to know the topology of its own domain and paths to reach each of other domain stephen

  20. Example of MBGP Intra-domain cloud Intra-domain cloud Intra-domain cloud Intra-domain cloud Multicast-capable Border router (running MBGP) Unicast-only Border router (running BGP) stephen

  21. Summary • Introduction of Multicast • Host Extension to IP multicast • Two examples of Intra-Domain Protocol for multicast – dense and sparse modes • Existing deployment: MBone • One example of Inter-Domain Protocol for multicast stephen

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