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1、,1,Chapter 12 Multicasting and Multicast Routing Protocols,IntroductionMulticast addresses and IGMPMulticast routingMulticast routing protocolMBONE,2,12.1 Introduction,IP Unicasting，IP单播通信One source One destination in the Internet unicast unicast address addressIP Multicasting，IP多播通信One source A gro
2、up of destinations in the Internet unicastmulticast address addressIP Broadcasting，IP广播通信One source All of destinations in one IP network unicastbroadcast address address,3,Data Link Layer,Physical multicast supportMost LANs support physical multicast addressingMapping IP multicast addresses to phys
3、ical multicast addressesNo physical multicast supportMost WANs DO NOT support physical multicast addressingUsing tunneling（隧道技术）to encapsulate the multicast IP packet in a unicast IP packet Or be encapsulated as link layer broadcast,4,Multicasting vs.Multiple Unicasting,Less bandwidthLess load of so
4、urceLess delay,More efficient,5,Multicast Applications,Access to distributed database访问分布式数据库Information dissemination信息传播Dissemination of News传播新闻Teleconferencing电视会议Distance learning远程学习,6,12.2 Multicast Address and IGMP,Multicast addressFunction:define a host groupIP multicast addressesMAC multic
5、ast addressesMapping class D to Ethernet MAC addressIGMPInternet Group Management Protocol网际组管理协议,7,12.2.1 IP Multicast Address,Allocation:IANA（RFC 3171）Class D:224.0.0.0239.255.255.255Local Network Control Block224.0.0.0/24:224.0.0.0224.0.0.255Not be forwarded by routerInternetwork Control Block224
6、.0.1.0/24:224.0.1.0224.0.1.255Must be forwarded through the InternetAdministratively Scoped Address Block239.0.0.0/8:239.0.0.0239.255.255.255类似于私有IP单播地址（如10.0.0.0/8）,8,12.2.2 MAC Multicast Address,IEEE MAC address formatStandard Group MAC AddressesAllocation:IEEE Registration AuthorityIEEE 802.1D MA
7、C Bridge Filtered MAC Group Addresses01-80-C2-00-00-0001-80-C2-00-00-0FStandard MAC Group Addresses01-80-C2-00-00-1001-80-C2-FF-FF-FFOthershttp:/standards.ieee.org/regauthIP-mapped Ethernet MAC group addresses01-00-5E-xx-xx-xx,xxxxxxxxx1,xxxxxxxx,xxxxxxxx,xxxxxxxx,xxxxxxxx,xxxxxxxx,bits,9,12.2.3 Map
8、ping Class D to Ethernet MAC Address,ExampleProblem:不明确的MAC地址IP多播地址:MAC多播地址25:132:1例:0 x0100.5E01.0101表示32个IP多播地址224.1.1.1,224.128.1.1,225.1.1.1,225.128.1.1,239.128.1.1,239.255.0.1,01-00-5E-7F-00-01,1110,Multicast ID:28 bits,Lost 5 bits,Prefix:25 bits,Multicast ID:23 bits,IP multicast address,MACadd
9、ress,Prefix,10,12.2.4 IGMP,Internet Group Management Protocol网际组管理协议Version 1:RFC 1112Version 2:RFC 2236Version 3:RFC 3376,RFC 4604FunctionUsed between hosts and multicast routers on a single physical networkHelp the multicast routers create and update a list of loyal members related to each router
10、interfaceNot a multicast routing protocol,but in conjunction with a multicast routing protocol to support IP multicasting,11,IGMP Operation,IGMP operates locallyJoining a groupLeaving a groupMonitoring membership,12,12.3 Multicast Routing,Objectives of multicastingOptimal routingMulticast forwarding
11、,13,12.3.1 Objectives of Multicasting,Every member of the group should receive one,and only one copy of the multicast packetNonmembers must not receive a copyThere must be no loops in routing,that is,a packet must not visit a router more than onceThe path traveled from the source to each destination
12、 must be optimal,14,12.3.2 Optimal Routing:Shortest Path Trees,Shortest path tree in unicast routingEach router has a routing table that defines a shortest path to possible destinationsRoot:each router itselfLeaf:possible destinationsShortest path tree in multicast routingEach involved router needs
13、to construct a shortest path tree for each groupTwo types of trees:source-based,group-shared,15,Shortest Path Tree in Unicast Routing,16,Flooding，洪泛,Flooding is related to both multicasting and broadcastingMethodForwards a packet out of all of its interfaces except the one from which the packet came
14、FeatureProvide broadcastingCreate loops and traffic jams:several copies of the same packet are circulated,17,Shortest Path Tree in Multicast Routing,Source-Based Tree源点基准树 or 有源树Each combination of source and group has a single treeEx.:N groups and M sources N x M treesNotation:(S,G)S多播源IP地址，G多播组地址G
15、roup-Shared Tree组共享树 or 共享树Each group shares the same treeSteiner tree,rendezvous-point tree（汇集点树，RPT）Ex.:N groups N treesNotation:(*,G)*所有的多播源，G多播组地址,18,Source-Based Tree,主机A,主机B,主机C,R1,R2,R4,R6,192.1.1.1,192.2.2.2,192.3.3.3,假设：A、B、C在多播组224.1.1.1中,R3,R5,19,Discuss:(S,G),（S,G）：最短路径树（SPT）树根：多播组G的信息源（
16、S）在具体的多播路由协议中，S通常指源子网树叶：多播组G的接收成员（S,G）是单向树多播信息流只能沿树的下行方向传播典型的多播路由协议DVMRP：单播D-V路由选择的扩展MOSPF：单播L-S路由选择的扩展PIM-DM：根据需要使用单播路由选择协议,20,Group-Shared Tree:RPT,主机A,主机B,主机C,R1,R2,R4,R6,192.1.1.1,192.2.2.2,192.3.3.3,R3,R5,主机D,192.4.4.4,根,主机E,192.5.5.5,(*,224.2.2.2),R5,R2,R4,C,R6,R3,B,D,假设：A、B、C、D、E在多播组224.2.2.2
17、中,R1,A,E,21,Bidirectional RPT,主机A,主机B,主机C,R1,R2,R4,R6,192.1.1.1,192.2.2.2,192.3.3.3,假设：A、B、C、D、E在多播组224.2.2.2中,R3,R5,主机D,192.4.4.4,(*,224.2.2.2),R5,R2,R1,R4,C,A,R6,R3,E,B,根,主机E,192.5.5.5,D,上行,下行,22,Unidirectional RPT,主机A,主机B,主机C,R1,R2,R4,R6,192.1.1.1,192.2.2.2,192.3.3.3,假设：A、B、C、D、E在多播组224.2.2.2中,R3
18、,R5,主机D,192.4.4.4,(*,224.2.2.2),R5,R2,R1,R4,C,A,R6,R3,E,B,根,主机E,192.5.5.5,D,下行,多播源如何将多播信息流送至根?,23,Unidirectional RPT+Source-Based Tree,主机A,主机B,主机C,R1,R2,R4,R6,192.1.1.1,192.2.2.2,192.3.3.3,假设：A、B、C、D、E在多播组224.2.2.2中,R3,R5,主机D,192.4.4.4,根,主机E,192.5.5.5,24,Unidirectional RPT+Unicast Tunneling,主机A,主机B,
19、主机C,R1,R2,R4,R6,192.1.1.1,192.2.2.2,192.3.3.3,假设：A、B、C、D、E在多播组224.2.2.2中,R3,R5,主机D,192.4.4.4,根,主机E,192.5.5.5,单播隧道,25,Discuss:RPT,RPT:（*,G）树根：多播组G的汇集点（RP）路由器静态指定RP：管理员根据需要指定动态选取RP：最高IP地址，RP哈希算法（RFC 2362）树叶：多播组G的接收成员多播组G的信息源S不一定在（*,G）上多播信息源S在RPT上：适合使用双向RPT多播信息源S不在RPT上：适合使用单向RPT典型的多播路由协议CBT：双向RPT（单播隧道：
20、信息源不在RPT上）PIM-SM：单向RPT有源树,汇集点路由器的最短路径树,26,有源树 vs.共享树,树根与多播源有源树的树根就是多播源无需静态指定或动态选取，多播源一定在有源树上共享树的树根不是多播源需静态指定或动态选取，多播源不一定在共享树上对多播路由器的影响共享树对多播路由器的资源消耗少于有源树有源树个数随（多播源，多播组）的增加而增加共享树个数随多播组的增加而增加多播数据流的传输延迟共享树的多播数据流的传输延迟大于有源树有源树是从多播源到所有组成员的最短路径树共享树只是从汇集点到所有组成员的最短路径树,27,Pruning,剪枝,剪掉树中没有多播接收成员分支的过程，有时效性例：,2
21、8,Grafting,嫁接,剪掉的分支上如果又出现了多播接收成员，则将其快速接回树上的过程例：,29,Pruning and Grafting,To create a multicast shortest path tree that supports dynamic membership changesTo make multicasting more efficient,30,12.3.3 Multicast Forwarding,Unicast forwardingUse the destination IP address in the IP packet to lookup the
22、unicast routing table to decide whether and how to forwardMulticast forwardingReverse path forwarding:逆向路径转发,RPFUse the source IP address in the IP packet to lookup the multicast routing table or the unicast routing table to decide whether to forwardOutgoing interface list:输出接口列表Constructed by the m
23、ulticast tree to perform the forwarding,Multicast forwarding cache,31,RPF Check Example 1,分组到达错误接口丢弃,S0,S1,PIM、CBT：单播路由表DVMRP：多播路由表,32,RPF Check Example 2,分组到达正确接口按输出接口表转发,S1,S1,33,Multicast Forwarding Cache,Multicast forwarding cache entryMulticast tree,incoming interface:RPF checkOutgoing interfac
24、e listExample:Cisco router(*,224.1.1.1),00:03:54/00:02:59,RP 10.1.5.1 Incoming interface:Serial0,RPF nbr 10.1.5.1 Outgoing interface list:Serial1,Forward/Sparse,00:01:43/00:02:11 Serial2,Forward/Sparse,00:03:54/00:02:06(171.68.37.121/32,224.1.1.1),00:00:25/00:02:53 Incoming interface:Serial0,RPF nbr
25、 10.1.5.1 Outgoing interface list:Serial2,Forward/Sparse,00:00:25/00:02:35,34,12.4 Multicast Routing Protocol,Multicast routing protocols,Source-Based Tree(S,G),Group-Shared Tree(*,G),MOSPF,PIM-DM,PIM-SM,CBT,DVMRP,PIM,Dense Mode,DM密集模式协议,Sparse Mode,SM稀疏模式协议,Link State链路状态协议,35,LS,DM and SM Protocol
26、s,LS（Link State，链路状态）协议通过扩散多播链路状态信息形成（S,G）DM（Dense Mode，密集模式）协议PUSH原理：假设网络中的每个子网内至少有一个多播数据流的接收站类比：电台广播或电视广播特性：（S,G），周期性的扩散和剪枝SM（Sparse Mode，稀疏模式）协议PULL原理：假设网络中初始没有多播接收站，除非显式加入类比：有线电视特性：（*,G），周期性的显式加入和剪枝,36,MOSPF,Multicast Open Shortest Path First多播开放最短路径优先，RFC 1584，RFC 1585An enhancement of OSPF v2U
27、ses IGMP to monitor multicast group membershipFloods the group-membership-LSA(type 6)throughout the routing domainA separate shortest-path tree is built on demand for each source network,multicast group combinationFeatureL-S,IGP,(S,G),LSForwarding cache entrylocal group database IGMPlink state datab
28、ase OSPF type 6 LSA,37,DVMRP,Distance Vector Multicast Routing Protocol距离向量多播路由选择协议，RFC 1075Combine many features of RIP with the truncated reverse path broadcasting(TRPB,截断反向路径广播)algorithmUses IGMP to exchange routing messagesSource network address,source network mask,hop countMaintains a multicast
29、 routing table to keep track of the return paths to the source of multicast packetsFeatureD-V,IGP,(S,G),DMForwarding cache entryMulticast routing table,38,PIM-DM,Protocol Independent Multicast Dense Mode协议无关多播密集模式，RFC 3973Uses the underlying unicast routing information base or a separate multicast-c
30、apable routing information baseNo to exchange routing messagesNo multicast routing tableFeatureProtocol independent(S,G),DMForwarding cache entryPIM Hello,Prune,and Graft messages:build(S,G)Unicast routing table:perform RPF check,39,PIM-SM,Protocol Independent Multicast Sparse Mode协议无关多播稀疏模式，RFC 460
31、1Uses the underlying unicast routing information base or a separate multicast-capable routing information baseNo to exchange routing messagesNo multicast routing tableFeatureProtocol independentUnidirectional(*,G)+(S,G),SMForwarding cache entryPIM Hello,Register,and Join/Prune messages:build(*,G)Uni
32、cast routing table:perform RPF check,40,CBT,Core-Based Tree有核树，RFC 2189(version 2,not be compatible with v1)May use a separate multicast routing table or the underlying unicast routing tableFeatureProtocol independentBidirectional(*,G)+Unicast Tunneling,SMForwarding cache entryCBT join messages:,Be gleaned from the routing table-the next hop to the specified core address.,41,12.5 MBONE,MBONE:multicast backbone,多播主干,42,12.6 Summary,多播地址IP多播地址：地址空间，是否可路由IPMAC多播地址映射：方法，问题IGMP：功能多播路由选择多播树：分类、特性、剪枝、嫁接多播转发：多播转发缓存、RFP机制多播路由协议分类、特性MBONE：概念,
