stp生成树协议培训

,生成树协议SpanningTreeProtocol,Objectives,RedundanttopologiesSpanningTreeProtocol,冗余（Redundancy）,冗余网络拓扑确保网络持续工作，避免单点故障Redundantnetworkingtopologiesaredesignedtoensurethatnetworkscontinuetofunctioninthepresenceofsinglepointsoffailure.,冗余拓扑（RedundantTopologies）,冗余拓扑（RedundantTopologies）,1.冗余拓扑的目标是为了避免网络出现单点故障Agoalofredundanttopologiesistoeliminatenetworkoutagescausedbyasinglepointoffailure.2.所有的网络需要冗余来提高可靠性Allnetworksneedredundancyforenhancedreliability.,简单的冗余交换拓扑（SimpleRedundantSwitchedTopology）,简单的冗余交换拓扑（SimpleRedundantSwitchedTopology）,1.冗余拓扑消除了单点故障Redundanttopologieseliminatesinglepointsoffailure.2.交换机对不知道地址的帧进行泛洪Switcheswillfloodframesforunknowndestinations.3.交换机对广播和组播也进行泛洪。Broadcastsandmulticastsarealsoflooded.4.冗余交换拓扑或许会带来广播风暴、多帧拷贝以及MAC地址表不稳定的问题Aredundantswitchedtopologymaycausebroadcaststorms,multipleframecopies,andMACaddresstableinstabilityproblems.,广播风暴（BroadcastStorm）,多帧传输（MultipleFrameTransmissions）,在冗余交换网络中，对终端设备来讲，收到多帧相同数据是可能的。Inaredundantswitchednetworkitispossibleforanenddevicetoreceivemultipleframes.,创建逻辑无环路拓扑（Creatingalogicalloopfreetopology）,1.冗余增加了可靠性，但是同时将物理环路带进网络。Reliabilityisincreasedbyredundancy.redundancyconnectionsintroducephysicalloopsintothenetwork.2.解决办法就是创建逻辑无环路拓扑，同时保留物理环存在Thesolutionistoallowphysicalloops,butcreatealoopfreelogicaltopology.3.无环路拓扑称为树，并且是可扩展的树。Theloopfreelogicaltopologycreatediscalledatree.Itisaspanningtreebecausealldevicesinthenetworkarereachableorspanned.4.创建无环路拓扑的算法称为生成树算法。Thealgorithmusedtocreatethisloopfreelogicaltopologyisthespanning-treealgorithm.,STP术语（STPTerms）,1.桥ID(BridgeID)2.开销（Cost）3.桥协议数据单元（BPDU）,桥ID(BridgeID),1.BID用来识别每一个交换机/网桥。2.BID用来确定网络的中心，在STP中称为根桥。3.优先级默认为32768TheBIDconsistsofabridgeprioritythatdefaultsto32768,开销（Cost）,最短路径是cost累加，而cost是基于链路的速率的。Shortestpathisbasedoncumulativelinkcosts.Linkcostsarebasedonthespeedofthelink.,桥协议数据单元（BPDU）,1.交换机发送的创建逻辑无环路的数据包称为BPDUThemessagethataswitchsends,allowingtheformationofaloopfreelogicaltopology,iscalledaBridgeProtocolDataUnit(BPDU).2.BPDU在阻塞的接口上也可以接收，这确保如果链路或设备出现问题，新的生成树会被计算BPDUscontinuetobereceivedonblockedports.Thisensuresthatifanactivepathordevicefails,anewspanningtreecanbecalculated.3.默认，BPDU2秒发送一次BydefaultBPDUsaresenteverytwoseconds.,Spanning-TreeProtocol,生成树操作（Spanning-TreeOperation）,Spanning-TreeOperation(cont.),1.选举根桥，BID最小即是Selectasingleswitchthatwillactastherootofthespanningtree2.计算自己到根桥距离Calculatetheshortestpathfromitselftotherootswitch3.选择根端口，距离根桥最近的接口Chooseoneofitsportsasitsrootport,foreachnon-rootswitch.Thisistheinterfacethatgivesthebestpathtotherootswitch.4.选指定端口和非指定端口，非指定端口被阻塞。Selectportsthatarepartofthespanningtree,thedesignatedports.Non-designatedportsareblocked.,生成树操作规则（Spanning-TreeOperationRules）,1.每个网络只有一个根桥Onerootbridgepernetwork.2.每个非根桥只有一个根端口Onerootportpernonrootbridge.3.每个段只有一个指定端口Onedesignatedportpersegment.4.非指定端口不被使用Nondesignatedportsareunused.,STP实例（STPExample）,生成树端口状态（Spanning-TreePortStates）,生成树端口状态（Spanning-TreePortStates）,1.在阻塞状态，端口仅能接收BPDU,需要20秒改变这种状态Intheblockingstate,portscanonlyreceiveBPDUs.Itmaytakeupto20secondstochangefromthisstate.2.在侦听状态，交换机确定是否有到根桥的其它路径。该状态持续15秒。在该状态，用户的数据不能转发，也不能学习MAC地址。Inlisteningstate,switchesdetermineifthereareanyotherpathstotherootbridge.theforwarddelayandlastsfor15seconds.Inthelisteningstate,userdataisnotbeingforwardedandMACaddressesarenotbeinglearned.,生成树端口状态（Spanning-TreePortStates）,3.在学习状态，用户的数据不能转发，但是可以学习MAC地址，该状态持续15秒。Inlearningstateuserdataisnotforwarded,butMACaddressesarelearnedfromanytrafficthatisseen.Thelearningstatelastsfor15secondsandisalsocalledtheforwarddelay.4.在转发状态，用户数据被转发，MAC地址继续学习，BPDU仍然工作。InforwardingstateuserdataisforwardedandMACaddressescontinuetobelearned.BPDUsarestillprocessed.,CaseStudy,Refertotheexhibit.AllswitcheshavethedefaultSTPconfigurationandalllinksareFastEthernet.WhichportonwhichswitchwillSpanningTreeplaceinblockingmode?,EnablingSpanningTree打开生成树协议,Switch(config)#spanning-treevlan200,EnablesspanningtreeonaspecificVLAN打开特定VLAN的生成树协议,默认时，所有VLAN的STP都是开启的，因此以上命令可以不配置,ConfiguringtheRootBridge配置根桥,Switch(config)#spanning-treevlan200priority4096,Lowersthespanningtreepriority,forcingthisswitchtobetherootbridge把网桥的优先级值降低，会使得网桥成为根桥,SettingPortCostandVLANPortCost设置端口的cost值,Switch(config-if)#spanning-treecost18,Configuresthespanningtreeportcostofaninterface配置端口的cost值,Switch(config-if)#spanning-treevlan200cost17,ConfiguresthespanningtreeVLANportcostofaninterfaceforaspecificVLAN可以在端口下为某一特定的VLAN指定cost值,VerifyingSTP检查STP,ASW11#showspanning-treevlan200VLAN0200SpanningtreeenabledprotocolieeeRootIDPriority49352Address0008.2199.2bc0ThisbridgeistherootHelloTime2secMaxAge20secForwardDelay15secBridgeIDPriority49352(priority49152sys-id-ext200)Address0008.2199.2bc0HelloTime2secMaxAge20secForwardDelay15secAgingTime300UplinkfastenabledInterfacePortIDDesignatedPortIDNamePrio.NbrCostStsCostBridgeIDPrio.Nbr-Fa0/1128.13019LIS0493520008.2199.2bc0128.1Fa0/2128.23019LIS0493520008.2199.2bc0128.2,Switch#showspanning-treevlanvlan-id,Displaysspanning-treeconfiguratio