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Network Protocols

Network Protocols. Multicast. Recall. Unicast Broadcast Multicast Unicast source address Group destination address (class D). Unicast one-to-one. Multicast one-to-many. Multicast operation questions. How do routers route/forward these packets?

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Network Protocols

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  1. Network Protocols • Multicast

  2. Recall • Unicast • Broadcast • Multicast • Unicast source address • Group destination address (class D)

  3. Unicast one-to-one

  4. Multicast one-to-many

  5. Multicast operation questions • How do routers route/forward these packets? • How do interested receivers learn about groups? • How do hosts join (and leave) groups? • What would be the MAC destination address? • What about security and reliability?

  6. IP multicast addressing • 224.0.0.0/4 (first 4 bits always 1110) • Registered, reserved and special use addresses • e.g. 224.0.0.0/24 – link local • 233.0.0.0/8 – GLOP addresses • IP to Ethernet MAC layer address mapping • IANA OUI = 00:00:5e (01:00:5e for multicast) • Map 23 low order IP bits to last 23 MAC bits • Yes, there is a mismatch (overlap of groups)

  7. Internet group management protocol (IGMP) • Host to router link layer signalling protocol • Hosts issue join/leave to signal interest or not • Routers use IGMP to build forwarding state • IGMPv1 - 1st generation, joins and queries • IGMPv2 – hosts can send explicit leave messages • IGMPv3 – hosts selectively specify sources • Required for source-specific multicast (SSM) • IGMPv3 not widely implemented yet

  8. IGMP packet format

  9. Multicast routing • Broadcast and prune (DVMRP, PIM-DM) • Reverse shortest path tree • Routers do reverse path forwarding (RPF) check • Explicit join (CBT, PIM-SM) • Receivers send join to rendezvous point (RP) • Senders send multicast data to RP, up the tree • RP fans out multicast data (its a meeting point) • Optimizations in PIM-SM to short-cut the RP • Shared tree versus source specific tree

  10. Distance vector multicast routing protocol (DVMRP) • Similar to RIP • Infinity = 32 hops • Flood everywhere first, prune back if necessary • Graft back leaf nodes if necessary, requires state • 1st generation multicast/MBONE – deprecated • Relatively poor scaling properties • PIM-DM is similar • Useful for dense population of group members

  11. Protocol independent multicast – sparse mode (PIM-SM) • Underlying unicast routing protocol is used • Receivers must explictly join groups (no flooding) • Everyone meets at a rendezvous point (RP) • RP is the core of a uni-directional tree • First hop routers encapsulate multicast to RP • RP can join source to the tree to avoid encap • State and reliability issues

  12. PIM-SM illustrated

  13. Multi-protocol BGP (MBGP) • BGP extension to carry other routes (e.g multicast) • Provides for route aggregation and policy • Used between ASes • Carries information about the sources of multicast

  14. Multicast source discovery protocol (MSDP) • A way for receivers to discover groups and sources • Connects PIM-SM domains together • MSDP peering routers exchange SA info • Source advertisements announced by senders • MSDP messages are flooded to all peers • State and flooding issues • Widely considered to be a temporary hack • ...but nothing better exists yet

  15. Internet IP multicast • From DVMRP MBONE to today's protocols • Widely deployed on Internet2 and intra-domain • IGMPv2/PIM-SM/MBGP/MSDP widely deployed • SSM addresses some scaling/security issues • DoS and state attacks still a significant risk • Common tools and applications deployed • IP/TV, sdr, mtrace, beacons, NUTV, on-the-i • University of Oregon has a lot of expertise

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