CCNA培训交换机原理及配置

©1999,CiscoSystems,Inc.—6-1交换机原理及配置©1999,CiscoSystems,Inc.—6-2学习内容1.交换机特点2.交换机的三种功能3.交换机的工作方式4.交换机的配置©1999,CiscoSystems,Inc.—6-3ABCD物理层•所有设备在同一冲突域•所有设备在同一广播域•所有设备共享相同的带宽1.交换机特点---集线器和交换机的区别©1999,CiscoSystems,Inc.—6-41.交换机特点集线器：同一个冲突域•接入设备越多冲突机率越大•用CSMA/CD技术•CarrierSense,MultipleAccesswithCollisionDetectionABC©1999,CiscoSystems,Inc.—6-5•每port有自己的冲突域•所有的port都在同一广播域数据链路层或1231241.交换机特点----交换机和网桥运行在链路层©1999,CiscoSystems,Inc.—6-6基于软件实现只有一个生成树实例最多16PortsBridging基于硬件实现(ASIC)多个生成数实例更多的PortsLANSwitching1.交换机特点----网桥与交换机比较©1999,CiscoSystems,Inc.—6-71.交换机特点•每个端口有自己的冲突域•广播包向所有port转发缓冲区交换©1999,CiscoSystems,Inc.—6-8•地址（MAC）学习•转发/筛选•环路避免2.交换机的三种功能----Switch的三个功能©1999,CiscoSystems,Inc.—6-92.交换机的三种功能-----Switches地址学习•初始MAC地址表为空•学习源地址MACaddresstable0260.8c01.11110260.8c01.22220260.8c01.33330260.8c01.4444E0E1E2E3ABCD©1999,CiscoSystems,Inc.—6-102.交换机的三种功能----Switches地址学习•StationAsendsaframetoStationC•SwitchcachesstationAMACaddresstoportE0bylearningthesourceaddressofdataframes•TheframefromstationAtostationCisfloodedouttoallportsexceptportE0(unknownunicastsareflooded)MACaddresstable0260.8c01.11110260.8c01.22220260.8c01.33330260.8c01.4444E0:0260.8c01.1111E0E1E2E3DCBA©1999,CiscoSystems,Inc.—6-112.交换机的三种功能------Switches地址学习•StationDsendsaframetostationC•SwitchcachesstationDMACaddresstoportE3bylearningthesourceAddressofdataframes•TheframefromstationDtostationCisfloodedouttoallportsexceptportE3(unknownunicastsareflooded)MACaddresstable0260.8c01.11110260.8c01.22220260.8c01.33330260.8c01.4444E0:0260.8c01.1111E3:0260.8c01.4444E0E1E2E3DCAB©1999,CiscoSystems,Inc.—6-122.交换机的三种功能------Switches转发/过滤•StationAsendsaframetostationC•Destinationisknown,frameisnotfloodedE0:0260.8c01.1111E2:0260.8c01.2222E1:0260.8c01.3333E3:0260.8c01.44440260.8c01.11110260.8c01.22220260.8c01.33330260.8c01.4444E0E1E2E3XXDCABMACaddresstable©1999,CiscoSystems,Inc.—6-13•StationDsendsabroadcastormulticastframe•Broadcastandmulticastframesarefloodedtoallportsotherthantheoriginatingport0260.8c01.11110260.8c01.22220260.8c01.33330260.8c01.4444E0E1E2E3DCABE0:0260.8c01.1111E2:0260.8c01.2222E1:0260.8c01.3333E3:0260.8c01.4444MACaddresstable广播与多播Frame©1999,CiscoSystems,Inc.—6-142.交换机的三种功能----冗余环路避免•冗余路径消除了单故障点•冗余路径的不利后果：•广播风暴,多个Frame副本,MAC地址表不稳定Segment1Segment2Server/hostXRouterY©1999,CiscoSystems,Inc.—6-15Segment1Segment2Server/hostXRouterYBroadcastSwitchASwitchBHostXsendsaBroadcast广播风暴©1999,CiscoSystems,Inc.—6-16Segment1Segment2Server/hostXRouterYBroadcastSwitchASwitchBHostXsendsaBroadcast广播风暴©1999,CiscoSystems,Inc.—6-17Segment1Segment2Server/hostXRouterYBroadcastSwitchescontinuetopropagatebroadcasttrafficoverandoverSwitchASwitchB广播风暴©1999,CiscoSystems,Inc.—6-18多个Frame副本Segment1Segment2Server/hostXRouterYUnicastSwitchASwitchB•HostXsendsanunicastframetorouterY•RouterYMACaddresshasnotbeenlearnedbyeitherswitchyet©1999,CiscoSystems,Inc.—6-19Segment1Segment2Server/hostXRouterYUnicastSwitchASwitchB•HostXsendsanunicastframetoRouterY•RouterYMACAddresshasnotbeenlearnedbyeitherSwitchyet•RouterYwillreceivetwocopiesofthesameframeUnicastUnicast多个Frame副本©1999,CiscoSystems,Inc.—6-20Segment1Segment2Server/hostXRouterYUnicastUnicastSwitchASwitchB•HostXsendsanunicastframetoRouterY•RouterYMACAddresshasnotbeenlearnedbyeitherSwitchyet•SwitchAandBlearnHostXMACaddressonport0Port0Port1Port0Port1多个Frame副本©1999,CiscoSystems,Inc.—6-21Segment1Segment2Server/hostXRouterYUnicastUnicastSwitchASwitchB•HostXsendsanunicastframetoRouterY•RouterYMACAddresshasnotbeenlearnedbyeitherSwitchyet•SwitchAandBlearnHostXMACaddressonport0•FrametoRouterYisflooded•SwitchAandBincorrectlylearnHostXMACaddressonport1Port0Port1Port0Port1多个Frame副本©1999,CiscoSystems,Inc.—6-22•Complextopologycancausemultipleloopstooccur•Layer2hasnomechanismtostoptheloopServer/hostWorkstationsLoopLoopLoop多个环路问题Broadcast©1999,CiscoSystems,Inc.—6-23解决办法:Spanning-TreeProtocol将一些Port置为Block状态，避免环路的产生Blockx©1999,CiscoSystems,Inc.—6-24•Onerootbridgepernetwork•Onerootportpernonrootbridge•OnedesignatedportpersegmentxDesignatedport(F)Rootport(F)Designatedport(F)Nondesignatedport(B)RootbridgeNonrootbridgeSWXSWY100baseT10baseT生成树协议STPSpanning-TreeOperations©1999,CiscoSystems,Inc.—6-25SwitchYDefaultpriority32768(8000hex)MAC0c0022222222SwitchXDefaultpriority32768(8000hex)MAC0c0011111111BPDUBPDU=Bridgeprotocoldataunit桥协议数据单元(2秒)Rootbridge：bridgeID最小的桥NonRootbridge：其它的桥BridgeID=Bridgepriority+bridgeMACaddress生成树协议——根桥选择©1999,CiscoSystems,Inc.—6-26SwitchYDefaultpriority32768MAC0c0022222222SwitchXDefaultpriority32768MAC0c0011111111RootbridgexPort0Port1Port0Port1100baseT10baseTDesignatedport(F)Rootport(F)Nondesignatedport(B)Designatedpo