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IP Multicast

IP Multicast. COSC 6590. Addressing. Class D address Ethernet broadcast address (all 1’s) IP multicast using Link-layer (Ethernet) broadcast Link-layer (Ethernet) multicast Both cases need filtering at IP layer. Source: unicast IP address S Receivers: multicast group ID G

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IP Multicast

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  1. IP Multicast COSC 6590

  2. Addressing • Class D address • Ethernet broadcast address (all 1’s) • IP multicast using • Link-layer (Ethernet) broadcast • Link-layer (Ethernet) multicast Both cases need filtering at IP layer. • Source: unicast IP address S Receivers: multicast group ID G • Each group is identified by (S, G)

  3. IPv4 Address Formats

  4. Mapping from Class D IP adress to Ethernet multicast adress

  5. Reverse Path Forwarding • If a packet is received on the interface that the router uses to send packets to the sender, only then will the packet be forwarded along the other interfaces. Otherwise, the packet will be dropped. • Building a loop-free broadcast tree • No knowledge of group membership

  6. Internet Group Management Protocol • For membership management. • Between a host on a subnet (Ethernet) and the router for the subnet. • The router periodically broadcast an IGMP host-membership query message on its subnet. • A host subscribes to a group replies by multicasting a host-membership report message. • Note: feedback implosion  uses a random timer. • The report is sent 3 times (for reliability). • IGMP-1: hosts send no report  leaving the group IGMP-2: hosts send explicit host-membership leave messages to reduce leave latency.

  7. Truncated Broadcasting • No members of a group on a subnet  leaf router will not forward packets of this group to the subnet (pruning). • Does not reduce traffic in the core network

  8. DVMRP • Distance Vector Multicast Routing Protocol • Leaf router sends a prune message to neighbouring routers when there is no group member on the subnet. • Intermediate routers perform pruning whenever possible. • Flooding and pruning are repeated periodically, when the current state times out. • Between flooding rounds, a host can re-join a group by sending a graft message. • Intermediate routers propagates the graft message upstream until the path is re-connected.

  9. MOSPF • Every router has the complete topology of its autonomous system. • A receiver joins a multicast group by exchanging IGMP messages with its end-router. • The end-router broadcasts the presence of this destination (group membership) to the whole network. • A sender simply sends data packets as they are available. • Each router uses the network topology, the group membership, and the multicast group ID in the data packets to compute the route(s) to the destination(s).

  10. MBone • Multicast backbone of the Internet • Not all routers support multicast routing protocols and IGMP. • Connecting multicast-capable routers using (virtual) IP tunnels

  11. References • Multicasting on the Internet and Its Applications, Sanjoy Paul, Kluwer Academic Publishers, 1998. • http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ipmulti.pdf • http://ntrg.cs.tcd.ie/undergrad/4ba2/multicast/bryan/index.html

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