l14 multicast forwarding, pim and multicast backbone

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1、Lecture14Multicastforwardingalgorithm,PIMandmulticastbackboneOutlineMulticastroutingconceptsMulticastTrees&RPFSpanningTreeAlgorithmsMulticastroutingprotocolsPIM-DMPIM-SMMulticastbackbone2MulticastRoutingConceptsMulticastdeliverytreeLocal:Hostinformsrouteraboutjoiningorleavinggroupusin

2、gIGMP.Wide-area:Localrouterinteractswithotherroutersusingmulticastroutingprotocols.4MulticastroutingprotocolsGoal:Tobuildaspanningtreebetweenallmembersofamulticastgroup.S5MulticastroutingasagraphproblemProblem:Howtoembedatreesuchthatallmulticastgroupmembersareconnectedbythetree?6Multi

3、castroutingasagraphproblemSolution1:ShortestPathTreeorsource-basedtreeBuildsatreethatminimizesthepathcostfromthesourcetoeachreceiver.Goodifthereisasinglesender.Iftherearemultiplesenders,needonetreepersender.Easytocompute.7MulticastroutingasagraphproblemSolution2:Minimum-CostTreeBuilds

4、atreethatminimizesthetotalcostoftheedgesGoodiftherearemultiplesenders.Veryexpensivetocompute(notpracticalformorethan30nodes).8MulticastTrees&RPFMulticastroutinginpracticeMulticastRoutingProtocolsimplementoneoftwoapproaches:SBT:Source-BasedTreeCBT:Core-BasedTreeorCenter-BasedTreeCBTisa

5、lsocalledshared-tree10SBTSource-BasedTreeEstablishareversepathtothesourceEssentiallyimplementsSolution1.BuildsoneshortestpathtreeforeachsenderThetreeisbuiltfromreceivertothesenderReverseshortestpathReversepathforwarding11CBTCore-BasedTreeEstablishareversepathtothecorerouterBuildsasi

6、ngletreesharedbyallsendersDoesnotuseSolution2becauseitistooexpensiveSelectsonerouterasa“core”/“rendezvouspoint”AllreceiversbuildashortestpathtothecoreReverseshortestpathReversepathforwarding12MulticastRoutingtableRoutingtableentriesforsource-basedtreesandforcore-basedtreesarediffere

7、ntSBT:(Source,Group)or(S,G)entryCBT:(*,G)entrySourceIPaddressMulticastgroupIncominginterface(RPFinterface)OutgoinginterfacelistS1G1I1I2,I3*G2I2I1,I313RPF:ReversepathforwardingRPFwantstobuildashortestpathtreeinadistributedfashionbytakingadvantageoftheunicastroutingtables.Mainconcept:Gi

8、venth