业务支撑网网络技术 Lesson 7 第二层交换机的功能.ppt

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1、Lesson7第二层交换机的功能7.1第二层交换机的工作原理7.2生成树协议(STP)7.3高级生成树协议7.4第二层交换机的基本配置7.5交换机的端口安全7.1第二层交换机的工作原理7.1.1面板指示灯7.1.2交换机和网桥的比较7.1.3交换机的数据转发方式7.1.4第二层交换机的功能7.1.5冗余(Redundant)7.1.1面板指示灯7.1.2交换机和网桥的比较网桥(Bridge)交换机(Switch)Cut-Through（直通转发）Switchchecksdestinationaddressandimmediatelybeginsforwardingfr

2、ameFragment-Free（碎片丢弃）Switchchecksthefirst64bytes,thenimmediatelybeginsforwardingframeStoreandForward（存储转发）Completeframeisreceivedandcheckedbeforeforwarding7.1.3交换机的数据转发方式7.1.4第二层交换机的功能地址学习(Addresslearning)转发/过滤决定(Forward/filterdecision)避免循环(Loopavoidance)MAC地址表(MACAddressTable)交换机上电初始

3、化期间MAC地址表是空的地址学习(LearningAddresses)StationAsendsaframetostationC.TheswitchcachestheMACaddressofstationAtoportE0bylearningthesourceaddressofdataframes.TheframefromstationAtostationCisfloodedouttoallportsexceptportE0(unknownunicastsareflooded).地址学习(LearningAddresses)StationDsendsaframetos

4、tationC.TheswitchcachestheMACaddressofstationDtoportE3bylearningthesourceaddressofdataframes.TheframefromstationDtostationCisfloodedouttoallportsexceptportE3(unknownunicastsareflooded).过滤帧(FilteringFrames)StationAsendsaframetostationC.Thedestinationisknown;theframeisnotflooded.过滤帧(Filte

5、ringFrames)StationAsendsaframetostationB.TheswitchhastheaddressforstationBintheMACaddresstable.StationDsendsabroadcastormulticastframe.Broadcastandmulticastframesarefloodedtoallportsotherthantheoriginatingport.广播MAC地址：FF.FF.FF.FF.FF.FF组播MAC地址范围：01:00:5E:00:00:00---01:00:5E:FF:FF:FF广播和组播

6、帧(BroadcastandMulticastFrames)7.1.5冗余(Redundant)优点：冗余能够避免单点故障缺点：交换循环(Switchloop)交换循环的危害广播风暴(BroadcastStorms)多帧复制(MultipleFramecopies)MAC地址表不稳定（MACDatabaseInstability）HostXsendsabroadcast.Switchescontinuetopropagatebroadcasttrafficoverandover.广播风暴(BroadcastStorms)HostXsendsaunicastframet

7、orouterY.TheMACaddressofrouterYhasnotbeenlearnedbyeitherswitch.RouterYwillreceivetwocopiesofthesameframe.多帧复制(MultipleFramecopies)HostXsendsaunicastframetorouterY.TheMACaddressofrouterYhasnotbeenlearnedbyeitherswitch.SwitchesAandBlearntheMACaddressofhostXonport0.Theframetoroute