ECE544: Communication Networks-II Spring 2012IP MulticastMulticast: one sender to many receiversSlide 4Slide 5Internet Multicast Service ModelMulticast groupsMapping IP Multicast Address to Ethernet AddressIPv6 Multicast Addresses (RFC 2375)Joining a mcast group: two-step processIGMP: Internet Group Management ProtocolHow IGMP WorksHow IGMP Works (cont.)Source Specific MulticastIGMPMulticast Routing: Problem StatementApproaches for building mcast treesShortest Path TreeReverse Path ForwardingBuilding the Reverse PathBuilding a Reverse Path TreeReverse Path Forwarding: exampleReverse Path Forwarding: pruningShared-Tree: Steiner TreeCenter-based treesCenter-based trees: an exampleCurrent Intra-Domain Multicast Routing ProtocolsCurrent Intra-Domain Multicast Routing Protocols (cont.)The First Intra-Domain Routing Protocol: DVMRPDistance-Vector Multicast Routing Protocol (DVMRP)Example TopologyPhase 1: Truncated BroadcastPhase 2: PruningSteady StateGrafting on New ReceiversSteady State after GraftingMulticast Routing: MOSPFMulticast OSPF (MOSPF)PowerPoint PresentationSlide 45Slide 46Slide 47Multicast Routing: PIMProtocol Independent Multicast (PIM)PIM Protocol OverviewPhase 1: Build Shared TreePhase 2: Sources Send to RPPhase 3: Stop EncapsulationPhase 4: Switch to Shortest Path TreePhase 5: Prune (S2 off) Shared TreeToday’s HomeworkReview Items for Mid-Term (1)Review Items for Mid-Term (2)Review Items for Mid-Term (3)Review Items for Mid-Term (4)Review Items for Mid-Term (5)Review Items for Mid-Term (6)ECE544: Communication Networks-II Spring 2012D. RaychaudhuriLecture 6Includes teaching materials from L. Peterson, J. Kurose, K. AlmerothIP Multicast•Introduction •Internet Group Management Protocol (IGMP)•Routing Protocols–Intra-domain (DVMRP, MOSPF, PIM)–Inter-domain (MBGP, MSDP) – not covered hereMulticast: one sender to many receivers •Multicast: act of sending datagram to multiple receivers with single “transmit” operation–One-to-many, many-to-many•Question: how to achieve multicastMulticast via unicast•source sends N unicast datagrams, one addressed to each of N receivers–Redundant traffic around sender–Keep track of all the IP addresses to send tomulticast receiver (red)not a multicast receiverRouters forward unicast datagramsMulticast: one sender to many receivers •Multicast: act of sending datagram to multiple receivers with single “transmit” operation–One-to-many, many-to-many•Question: how to achieve multicastNetwork multicast (IP Multicast)•Routers actively participate in multicast, making copies of packets as needed and forwarding towards multicast receiversMulticast routers (red) duplicate and forward multicast datagramsMulticast: one sender to many receivers •Multicast: act of sending datagram to multiple receivers with single “transmit” operation–One-to-many, many-to-many•Question: how to achieve multicastApplication-layer multicast (P2P)•end systems (“hosts”) involved in multicast copy and forward unicast datagrams among themselves•“host” becomes routerP2P hosts duplicate and forward multicast datagramsInternet Multicast Service Modelmulticast group concept: –Each group has its own IP multicast address–A host can join or leave freely–Routers forward multicast datagrams (with destination address of the group’s multicast address) to hosts that have “joined” that multicast group128.119.40.186128.59.16.12128.34.108.63128.34.108.60multicast group226.17.30.197Multicast groupsclass D Internet addresses reserved for multicast:host group semantics:oanyone can “join” (receive) or leave multicast groupoanyone (not even a member) can send to multicast groupono network-layer identification of hosts membersneeded: infrastructure to deliver mcast-addressed datagrams to all hosts that have joined that multicast groupMapping IP Multicast Address to Ethernet Address •Ethernet MAC Addresses: 48 bits–broadcast: all 1s, ff:ff:ff:ff:ff:ff–multicast: multicast flag (the lowest bit of the 1st octet)= 1•01-00-5E-00-00-00 to 01-00-5E-7F-FF-FF for IP multicast•IP multicast group address mapped to the lower order 23 bits of MAC address •not one-to-one mapping, one Ethernet mcast addr 32 IP mcast addrsIPv6 Multicast Addresses (RFC 2375)•low-order flag indicates permanent / transient group; three other flags reserved•scope field: 1 - node local–2 - link-local–5 - site-local–8 - organization-local–B - community-local–E - global–(all other values reserved)4 112 bits8group IDscopeflags111111114Joining a mcast group: two-step process•local: host informs local mcast router of desire to join group: IGMP (Internet Group Management Protocol)•wide area: local router interacts with other routers to receive mcast datagram flow–many protocols (e.g., DVMRP, MOSPF, PIM)IGMPIGMPIGMPwide-areamulticast routingIGMP: 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 queryqueryreportHow IGMP Works•on each link, one router is elected the “querier”•querier periodically sends a Membership Query messageto the all-systems group (224.0.0.1), with TTL = 1•on receipt, hosts start random timers (between 0 and 10 seconds) for each multicast group to which they belong Qrouters:hosts:How IGMP Works (cont.)•when a host’s timer for group G expires, it sends a Membership Report to group G, with TTL = 1•other members of G hear the report and stop their timers•routers hear all reports, and time out non-responding groupsQG G G GSource Specific Multicast•Source Specific Multicast: a receiving host specifies (source, mcast group) to join–receive multicast packets addressed to the group and only if they are from the specific sender (one-to-many)•Any source multicast (ASM): many-to-manyIGMPIGMP 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 1112IGMP 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 2236IGMP v3: –Join/Leave
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