路由交换第十七章STP.ppt

生成树协议SpanningTreeProtocol 教学目标 Objectives 1 IP地址概念 ConceptofIPAddress 2 IP地址分类 ClassofIPAddress 3 保留和私有地址 ReservedandPrivateIPAddress 4 网络掩码和子网划分 NetworkMaskandSubnetting 5 可变长度子网掩码 VLSM 6 汇总和CIDR SummarizationandCIDR 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 MAC地址表不稳定 MACDatabaseInstability 交换机从错误的接口学到MAC地址 AswitchcanlearnthataMACaddressisonaportwhenitisnot 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 WhichportonwhichswitchwillSp