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Introduction to IP Multicast David Meyer Cisco Systems

Introduction to IP Multicast David Meyer Cisco Systems. 0940_03F8_c1 NW97_US_106. Agenda. IP Multicast Technology and Concepts IP Multicast Host-to-Router Protocols IP Multicast Routing Protocols Protocol Independent Multicast—PIM General Multicast Concepts

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Introduction to IP Multicast David Meyer Cisco Systems

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  1. Introduction to IP MulticastDavid Meyer Cisco Systems 0940_03F8_c1 NW97_US_106

  2. Agenda • IP Multicast Technology and Concepts • IP Multicast Host-to-Router Protocols • IP Multicast Routing Protocols • Protocol Independent Multicast—PIM • General Multicast Concepts • Inter-domain Multicast Routing • Issues and Solutions

  3. Introduction to Multicast • Why multicast? • When sending same data to multiple receivers • Better bandwidth utilization • Lesser host/router processing • Receivers’ addresses unknown • Applications • Video/audio conferencing • Resource discovery/service advertisement • Stock distribution • Eg. Vat, Vic, IP/TV, Pointcast

  4. Unicast/Multicast Unicast Host Router Multicast Host Router

  5. IP Multicast Service Model • RFC 1112 • Each multicast group identified by a class D IP address • Members of the group could be present anywhere in the Internet • Members join and leave the group and indicate this to the routers • Senders and receivers are distinct: i.e., a sender need not be a member • Routers listen to all multicast addresses and use multicast routing protocols to manage groups

  6. IP Multicast Service Model (Cont.) • IP group addresses • Class D address—high-order 3 bits are set (224.0.0.0) • Range from 224.0.0.0 through 239.255.255.255 • Well known addresses designated by IANA • Reserved use: 224.0.0.0 through 224.0.0.255 • 224.0.0.1—all multicast systems on subnet • 224.0.0.2—all routers on subnet • Transient addresses, assigned and reclaimed dynamically • Global scope: 224.0.1.0-238.255.255.255 • Limited scope: 239.0.0.0-239.255.255.255 • Site-local scope: 239.253.0.0/16 • Organization-local scope: 239.192.0.0/14

  7. IP Multicast Service Model (Cont.) • Mapping IP group addresses to data link multicast addresses • RFC 1112 defines OUI 0x01005e • Low-order 23-bits of IP address map into low-order 23 bits of IEEE address (eg. 224.2.2.2–01005e.020202) • Ethernet and FDDI use this mapping • Token Ring uses functional address-c000.4000.0000

  8. IP Multicast Service Model (Cont.) Host-to-Router Protocols (IGMP) Hosts Routers Multicast Routing Protocols (PIM)

  9. Internet Group Management Protocol—IGMP • How hosts tell routers about group membership • Routers solicit group membership from directly connected hosts • RFC 1112 specifies first version of IGMP • IGMP v2 and IGMP v3 enhancements • Supported on UNIX systems, PCs, and MACs 0940_03F8_c1 NW97_US_106 9

  10. Internet Group Management Protocol—IGMP • IGMP v1 • Queries • Querier sends IGMP query messages to 224.0.0.1 with ttl = 1 • One router on LAN is designated/elected to send queries • Query interval 60–120 seconds • Reports • IGMP report sent by one host suppresses sending by others • Restrict to one report per group per LAN • Unsolicited reports sent by host, when it first joins the group 0940_03F8_c1 NW97_US_106 10

  11. IGMP—Joining a Group 224.2.0.1224.5.5.5 224.2.0.1 224.2.0.1 Host 1 Host 2 Host 3 Sends Reportto 224.2.0.1 Sends Reportto 224.5.5.5 Periodically SendsIGMP Query to 224.0.0.1

  12. Internet Group Management Protocol—IGMP • IGMP v2: • Host sends leave message if it leaves the group and is the last member (reduces leave latency in comparison to v1) • Router sends G-specific queries to make sure there are no members present before stoppingto forward data for the group for that subnet • Standard querier election • IGMP v3: • In design phase • Enables to listen only to a specified subset of the hosts sending to the group

  13. IGMP—Leaving a Group 224.2.0.1 224.2.0.1 224.2.0.1 Host 1 Host 2 Host 3 Sends Reportfor 224.2.0.1 Sends Leavefor 224.2.0.1to 224.0.0.2 Sends Leavefor 224.5.5.5to 224.0.0.2 Sends Group SpecificIGMP Query to 224.2.0.1 Sends Group SpecificIGMP Query to 224.5.5.5

  14. Multicast Routing Protocols(Reverse Path Forwarding) • What is RPF? • A router forwards a multicast datagram if received on the interface used to send unicast datagrams to the source Unicast C B Receiver Source A F D E Multicast

  15. Multicast Routing Protocols(Reverse Path Forwarding) • If the RPF check succeeds, the datagram is forwarded • If the RPF check fails, the datagram is typically silently discarded • When a datagram is forwarded, it is sent out each interface in the outgoing interface list • Packet isneverforwarded back out the RPF interface!

  16. A B D F Multicast Routing Protocols—Characteristics Shortest Path or Source Distribution Tree Source Notation: (S, G) S = Source G = Group C E Receiver 1 Receiver 2

  17. Multicast Routing Protocols—Characteristics Shared Distribution Tree Source 1 Notation: (*, G) * = All Sources G = Group Source 2 A B F D (Shared Root) C E Receiver 1 Receiver 2

  18. Multicast Routing Protocols—Characteristics • Distribution trees • Source tree • Uses more memory O(S x G) but you get optimal paths from source to all receivers, minimizes delay • Shared tree • Uses less memory O(G) but you may get suboptimal paths from source to all receivers, may introduce extra delay • Protocols • PIM, DVMRP, MOSPF, CBT

  19. Multicast Routing Protocols—Characteristics • Types of multicast protocols • Dense-mode • Broadcast and prune behavior • Similar to radio broadcast • Sparse-mode • Explicit join behavior • Similar to pay-per-view

  20. Multicast Routing Protocols—Characteristics • Dense-mode protocols • Assumes dense group membership • Branches that are pruned don’t get data • Pruned branches can later be grafted to reduce join latency • DVMRP—Distance Vector Multicast Routing Protocol • Dense-mode PIM—Protocol Independent Multicast

  21. Multicast Routing Protocols—Characteristics • Sparse-mode protocols • Assumes group membership is sparsely populated across a large region • Uses either source or shared distribution trees • Explicit join behavior—assumes no one wants the packet unless asked • Joins propagate from receiver to source or Rendezvous Point (Sparse mode PIM) or Core (Core Based Tree)

  22. DVMRP • Broadcast and prune • Source trees created on demand based on RPF rule • Uses own routing table • e.g., use of poison reverse • Tunnels to overcome incongruent topologies • Many implementations • mrouted, Bay, … • Cisco • draft-ietf-idmr-dvmrp-v3-06.{txt,ps}

  23. Dense Mode PIM • Broadcast and prune “ideal” for dense groups • Source trees created on demand based on RPF rule • If the source goes inactive, the tree is torn down • Fewer implementations than DVMRP • Draft: draft-ietf-idmr-pim-dm-spec-05.txt

  24. Dense Mode PIM • Branches that don't care for data are pruned • Grafts to join existing source tree • Uses asserts to determine forwarder for multi-access LAN • Prunes on non-RPF P2P links • Rate-limited prunes on RPF P2P links

  25. Link Data Control A B G C D F H E I Dense Mode PIM Example Source Receiver 1 Receiver 2

  26. A B G C D F H E I Dense Mode PIM Example Source Initial Flood of Dataand Creation of State Receiver 1 Receiver 2

  27. A B G C D F H E I Dense Mode PIM Example Source Prune to Non-RPF Neighbor Prune Receiver 1 Receiver 2

  28. A B G C D F H E I Dense Mode PIM Example Source C and D Assert to DetermineForwarder for the LAN, C Wins Asserts Receiver 1 Receiver 2

  29. A B G C D F H E I Dense Mode PIM Example Source I Gets Pruned E’s Prune is Ignored G’s Prune is Overridden Prune Join Override Prune Receiver 1 Receiver 2

  30. A B G C D F H E I Dense Mode PIM Example Source New Receiver, I Sends Graft Graft Receiver 1 Receiver 2 Receiver 3

  31. A B G C D F H E I Dense Mode PIM Example Source Receiver 1 Receiver 2 Receiver 3

  32. Sparse Mode PIM • Explicit join model • Receivers join to the Rendezvous Point (RP) • Senders register with the RP • Data flows down the shared tree and goes only to places that need the data from the sources • Last hop routers can join source tree if the data rate warrants by sending joins to the source • RPF check for the shared tree uses the RP • RPF check for the source tree uses the source

  33. Sparse Mode PIM • Only one RP is chosen for a particular group • RP statically configured or dynamically learned (Auto-RP, PIM v2 candidate RP advertisements) • Data forwarded based on the source state (S, G) if it exists, otherwise use the shared state (*, G) • Draft: draft-ietf-idmr-pim-sm-specv2-00.txt • Draft: draft-ietf-idmr-pim-arch-04.txt

  34. Link Data Control Sparse Mode PIM Example Source A B D RP C E Receiver 1 Receiver 2

  35. Sparse Mode PIM Example Receiver 1 Joins Group GC Creates (*, G) State, Sends(*, G) Join to the RP Source A B D RP Join C E Receiver 1 Receiver 2

  36. Sparse Mode PIM Example RP Creates (*, G) State Source A B D RP C E Receiver 1 Receiver 2

  37. Sparse Mode PIM Example Source Sends DataA Sends Registers to the RP Source Register A B D RP C E Receiver 1 Receiver 2

  38. Sparse Mode PIM Example RP de-encapsulates RegistersForwards Data Down the Shared TreeSends Joins Towards the Source Source Join Join A B D RP C E Receiver 1 Receiver 2

  39. Sparse Mode PIM Example RP Sends Register-Stop OnceData Arrives Natively Source Register-Stop A B D RP C E Receiver 1 Receiver 2

  40. Sparse Mode PIM Example C Sends (S, G) Joins to Join theShortest Path (SPT) Tree Source A B D RP (S, G) Join C E Receiver 1 Receiver 2

  41. Sparse Mode PIM Example When C Receives Data Natively,It Sends Prunes Up the RP tree forthe Source. RP Deletes (S, G) OIF andSends Prune Towards the Source Source (S, G) Prune A B D RP (S, G) RP Bit Prune C E Receiver 1 Receiver 2

  42. Sparse Mode PIM Example New Receiver 2 JoinsE Creates State and Sends (*, G) Join Source A B D RP (*, G) Join C E Receiver 1 Receiver 2

  43. Sparse Mode PIM Example C Adds Link Towards E to the OIFList of Both (*, G) and (S, G)Data from Source Arrives at E Source A B D RP C E Receiver 1 Receiver 2

  44. Sparse Mode PIM Example New Source Starts SendingD Sends Registers, RP Sends JoinsRP Forwards Data to Receiversthrough Shared Tree Source Register Source 2 A B D RP C E Receiver 1 Receiver 2

  45. Inter-domain Multicast Routing 1037_03F8_c2 NW98_US_114

  46. Agenda • Introduction • First Some Basic Technology • Basic Host Model • Basic Router Model • Data Distribution Concepts • What Are the Deployment Obstacles • What Are the Non-technical Issues • What Are the Technical Scaling Issues

  47. Agenda (Cont.) • Potential Solutions (Cisco Specific) • Multi-level RP, Anycast Clusters, MSDP • Using Directory Services • Industry Solutions • BGMP and MASC • Possible Deployment Scenarios • References

  48. Introduction—Level Set • This presentation focuses on large-scale multicast routing in the Internet • The problems/solutions presented are related to inter-ISP deployment of IP multicast • We believe the current set of deployed technology is sufficient for enterprise environments

  49. Introduction—Why Would You Want to Deploy IP Multicast? • You don’t want the same data traversing your links many times— bandwidth saver • You want to join and leave groups dynamically without notifying all data sources—pay-per-view

  50. Introduction—Why Would You Want to Deploy IP Multicast? • You want to discover a resource but don’t know who is providing it or if you did, don’t want to configure it— expanding ring search • Reduce startup latency for subscribers

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