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SDNControllerChallengesTheStoryThusFarSDN---centralizethenetwork’scontrolplaneThecontrolleriseffectivelythebrainofthenetworkControllerdetermineswhattodoandtellswitcheshowtodoit.TheStoryThusFarTheStoryThusFarSomethingHappened!!!!TheStoryThusFarLet’sAsktheBrian!!!!TheStoryThusFarThinkaboutwhathappen…MaybecomeupwithasolutionTheStoryThusFarControllerrunscontrolfunctionControlfunctioncreatesswitchstateF(globalnetworkstate)SwitchstateGlobalnetworkstatecanbegraphofthenetworkTellthenetworkwhattodoChallengeswithCentralizationSinglepointoffailureFaulttolerancePerformancebottleneckScalabilityEfficiency(switch-controllerlatency)SinglepointforsecurityviolationsMotivationforDistributedControllersWide-Area-NetworkWidedistributionofswitches:fromUSAtoAustralia.HighlatencybetweenonecontrollerandAllswitchesApplication+NetworkgrowthHigherCPUloadforcontrollerMorememoryforstoringFIBentriesandcalculationsHighavailabilitClassOutlineFaultToleranceGoogle’sB4paperControllerScalabilityWaystoscalethecontrollerDistributedcontrollers:MeshVersusHierarchyImplicationsofcontrollerplacementFaultToleranceGoogle’sB4NetworkProvidesconnectivitybetweenDCsitesUsesSDNtocontroledgeswitchesGoal:highutilizationoflinksInsight:fine-grainedcontroloveredgeandnetworkcanleadtohigherutilizationDistributedControllersOnesetofcontrollersforeachDatacenter(site)Google’sB4NetworkProvidesconnectivitybetweenDCsitesUsesSDNtocontroledgeswitchesGoal:highutilizationoflinksDistributedControllersOnesetofcontrollersforeachDatacenter(site)FaultToleranceinB4 EachsiterunsasetofcontrollerPaxosisrunbetweencontrollersinasitetodeterminemasterQuickOverviewofPaxosGivenNcontrollers1Actsasleader,andN-1asworkersAllNcontrollermaintainthesamestateSwitchesinteractwithleaderChangedoesn’thappenuntilwholegroupagreesFailureofprimaryN-1worktogethertoelectanewleader(determinenewleader)NetworkEventsPropagateStatechangesPros-ConsofPaxosProsWellunderstoodandstudied;givesgoodFTManyimplementationsinthewildE.g.ZookeeperConsTimetorecoverImpactsthroughoftheputoftheentiresystemControllerScalabilityWhatlimitsacontroller’sscalability?NumberofcontrolmessagesfromswitchDependsontheapplicationlogicE.g.MicroTE/HederaperiodicallyqueryallswitchesforstatsReactivecontroller,evaluatedinNoX,requireseachswitchtosendmessagesforanewflowPacket-in(ifreactiveApps)Flowstats,Flow_time-outsWhatlimitsacontroller’sscalability?ApplicationprocessingoverheadThecontrollerrunsabunchofapplicationSimilarto:AserverrunningasetofprogramsCPU/MemoryconstraintlimithowtheapprunsWhatlimitsacontroller’sscalability?DistancebetweencontrollerandtheswitchesController1HederaL3FWHowtoScaletheController.Obvious:addmorecontrollers.BUT:howabouttheapplications?Synchronization/concurrencyproblems.Whocontrolswhichswitch?Whoreactstowhichevents?Controller1HederaL3FWController2HederaL3FWControllerNHederaL3FW??Stats+InstallOFentriesMediumSizedNetworksAssumption:controllercan’tstoreallforwardingtableentriesinmemoryButcanprocessalleventsandrunallappsEachcontrollerGetsamenetworkevents+runningsameapp.sameoutputButstoreoutputforonlyafractionandconfigonlyafractionController1HederaL3FWController2HederaL3FWControllerNHederaL3FWStats+InstallOFentriesMediumSizedNetworks:hyperflowEachcontrollerPushstatetoeachcontrollerEachcontrollerthingsit’stheonlyoneinthenetworkController1HederaL3FWController2HederaL3FWControllerNHederaL3FWStats+InstallOFentriesSub-subscribessytemLargeSizedNetworksAssumptionsEachcontrollercan’tstorealltheFIBentriesEachcontrollercan’truntheentireapplicationorhandleeventsNeedtopartitiontheapplicationButhow?Applicationpartition1Approach1:eachcontrollerrunsaspecificapplicationHowdoyourresolveconflictsinFWentriesAppscanconflictintherulestheyinstallController1HederaController2L3ControllerNFWApplicationpartition2Approach2:allcontrollersrunthesameapplicationbutforasubsetofdevicesResultsinaDistributedMeshcontrolplaneController1HederaL3FWController2HederaL3FWControllerNHederaL3FWAbstractNetworkviewApplicationPartition2AbstractviewexchangedwitheachotherAbstractviewreducesthen/winformationusedbyeachcontrollerController2HederaL3FWREALNETWORKController2’sViewofNETWORKAbstractionProvidedbyController1AbstractionProvidedbyControllerNONIXtotheSDNProgrammerControllerssynchronizethroughaDBorDHTSoeachappneedssynchronizationcode.Howdoyoudealwithconcurrency.Howtosynchronizebetweendomains.Howmanydomains?Orcontrollers?Howmanyswitchesinadomain?Applicationpartition3Approach3:divideapplicationintolocal,andglobal.ResultsinahierarchicalcontrolplaneGlobalControllerandLocalControllersApplicationsthatdonotneednetwork-widestateCanberunlocallywithoutcommunicatewithothercontrollersAreHierarchicalControllersFeasibleExamplesoflocalapplications:LinkDiscovery,Learningswitch,localpoliciesExamplesoflocalportionsofaglobalalgoDatacenterTrafficengineeringElephantflowdetection(hedera)Predictabilitydetection(MicroTE)Localapps/controllershaveotherbenefitsHighparallelismCanberunclosertothedevices.Kandoo:HierarchicalcontrollersController1HederaL3FWController2HederaL3FWControllerNHederaL3FWGlobalControllerHedera2levelsofcontrollers:globalandlocalLocalapplicationsareembarrassinglyparallelLocalshieldsglobalfromnetworkeventsKandoo:HierarchicalcontrollersController1HederaL3FWController2HederaL3FWControllerNHederaL3FWGlobalControllerHederaLocalControllers:runlocalappsReturnsabstractviewtotheglobalcontrollerReduces#eventssenttoglobalandreducesizeofnetworkseenbyKandoo:HierarchicalcontrollersController1HederaL3FWController2HederaL3FWControllerNHederaL3FWGlobalControllerHederaGlobalControllersRunsglobalapps:AKAappsthatneednetworkwidestateHederaReminderGoal:reducenetworkcontentionInsight:contentionhappenswhenelephantssharepaths.Solution:DetectElephantflowsPlaceElephantflowsondifferentflowsImplementingHederainOnixController1Hedera:detection+placementController2Hedera:

detection+placement2levelsofcontrollers:globalandlocalLocalapplicationsareembarrassinglyparallelLocalshieldsglobalfromnetworkeventsStatsStatsFlowTableentriesFlowTableentriesExchangeTM+detectionImplementingHederainKandooController1ElephantdetectionController2ControllerNGlobalControllerHedera:GlobalplacementLocalControllers:getstatsfromnetworks+elephantdetectionGlobalController:decideflowplacement+flowinstallationElephantdetectionElephantdetectionInformof

elephantflowsStatsInstallnewflowtableentriesImplementingB4inKandoolikearchitectureSiteControllerElephantdetectionSiteController2SiteControllerNGlobalControllerTE+BWallocatorLocalControllers:getstatsfromnetwork