static and dynamic routing静态和动态路由

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1、NetworkingBasicsB.KonkothLesson13–NetworkLayerStaticandDynamicRoutingWhenitcomestorouting,thereisahugedifferencebetweenthetwotypesofrouting:staticanddynamic.Earlyroutershadtobeprogrammedwithexactlywhichnetworkstheycouldroutebetweenwhichinterfaces,especiallyiftherewe

2、remanynetworkinterfaces.Thisiscalledstaticrouting,whichconsistsofadding,maintaining,anddeletingroutesofthenetworkroutingdevicesbythenetworkadministrator.Inasmallcompanythismaynotbemuchofachore,butformediumtolargenetworks,thiscanbenearlyimpossible.Theselargernetworks

3、almostalwaysemploymanylogicalsubnets,whichrequiresyoutoupdatetheroutetablesoneachroutingdevice.Iftheseremotesubnetsareconnectedbyrouterswithstaticroutetables,youhavetoaddtheexactstaticrouteinordertocommunicatebetweenthetwosubnets.Tablebelowgivesyouanexampleofwhatisc

4、ontainedintheroutingtable.Destination AdjacentRouterHopsNetwork1RouterA1Network1RouterB2Network2RouterB2Network2RouterC3Network3RouterD3AnExampleofaRoutingTableInthistableyoucanseehowyouonlyspecifytheroutertobeusedtoreachyourdestination,nottheactualdestinationitself

5、.AlsonoticethecolumnforHops.Thisiswhatdetermineswhichrouteisthemostefficient,similarto“NameThatTune.”Ifarouteclaimsitcanreachthedestinationinonefewerhopthanthenextrouter,thenlethimproveit.Iftherearetwoidenticalroutestothesamedestination,theroutewiththefewesthopswill

6、beused. Onechangetoanetworkaddressmeansvisitingeveryroutingdevicethatemploysstaticroutingandupdatingtheentry.Whatdowedoifournetworkisfairlylargeandcomplex?Wemustthenuseroutingdevicescapableofdynamicallyupdatingtheroutetables.Dynamicroutingdoesnotrequirethenetworkadm

7、inistratortoeditcomplexroutingtablesinordertocommunicatewithothernetworksorsegments.TheserouterscommunicatewitheachotherusingapowerfulroutingprotocolsuchasRoutingInformationProtocol(RIP)orOpenShortestPathFirst(OSPF).Theycanalsoqueryotherroutersforupdatedrouteinforma

8、tion,whichcancreatemoreefficientpathsforsendingpacketsorlocateanalternativerouteiftheoriginalroutefails.Therouterscanbroadcasttheroutesthe