STP(生成树协议讲解)ppt课件

STP,局域网中通常会存在冗余链路。需要一种方法阻塞冗余链路，消除路径环路，并且在必要时将冗余链路自动切换为转发状态，恢复网络的连通性。生成树协议就可以实现这样的功能。生成树协议包括STP、RSTP、MSTP等。本章对STP的工作原理进行详细介绍。,引入,了解STP消除环路的思想掌握STP的基本概念掌握STP计算过程掌握STP的端口状态掌握STP拓扑改变处理过程了解STP的不足,课程目标,学习完本课程，您应该能够：,STP介绍STP基本概念STP计算过程STP端口状态STP拓扑改变处理过程STP协议的不足,目录,Page4,交换机转发流程回顾,E0/2,E0/3,E0/5,E0/6,00-0D-56-BF-88-10,00-0D-56-BF-88-20,PCA,SWA,SWB,PCB,Page5,环路引起的问题之一广播风暴,PCA,SWA,SWB,广播,Page6,交换机学习MAC地址表回顾,E0/2,E0/3,E0/5,E0/6,00-0D-56-BF-88-10,00-0D-56-BF-88-20,PCA,SWA,SWB,PCB,Page7,E0/3,E0/4,E0/5,E0/6,PCA,SWA,SWB,00-0D-56-BF-88-10,E0/2,00-0D-56-BF-88-10,E0/2,00-0D-56-BF-88-10,E0/4,错误目的端口,环路引起的问题之二MAC地址表不稳定,什么是STP？,STP是二层网络中用于消除环路的协议通过阻断冗余链路来消除桥接网络中可能存在的路径回环当前活动路径发生故障时，激活冗余备份链路，恢复网络连通性,ROOT,PhysicalSegmentA,PhysicalSegmentB,PhysicalSegmentC,PhysicalSegmentD,PhysicalSegmentE,STP消除环路的思想,将网络拓扑修剪为树形选择树根节点确定最短路径阻塞冗余链路,ROOT,PhysicalSegmentA,PhysicalSegmentB,PhysicalSegmentC,PhysicalSegmentD,PhysicalSegmentE,STP介绍STP基本概念STP计算过程STP端口状态STP拓扑改变处理过程STP协议的不足,目录,桥和端口的角色,桥的角色：根桥指定桥端口角色：根端口指定端口Alternate端口,根桥,根端口,根端口,指定端口,指定端口,指定端口,Alternate端口,指定桥SWA,SWB,SWC,SWA,指定桥SWB,桥ID,桥ID用于在STP中唯一的标识一个桥，桥ID由两部分组成，长度为8个字节桥优先级：高16位(065535,默认32768)优先级（16bit）=4Bit桥优先级+12Bit扩展系统IDMAC地址：低48位,路径开销（PathCost）,路径开销用于衡量桥与桥之间路径的优劣STP中每条链路都具有开销值路径开销等于路径上全部链路开销之和,SWB,SWC,SWA,1Gig,1Gig,Cost20,Cost200,100M,链路开销标准,配置BPDU,网桥通过交互配置BPDU获取STP计算所需要的参数配置BPDU基于二层组播方式发送，目的地址为01-80-C2-00-00-00配置BPDU由根桥周期发出，发送周期为HelloTime。配置BPDU老化时间为MaxAge。,SWA,SWB,配置BPDU,Root,SWC,配置BPDU,配置BPDU格式,DMA:目的MAC地址SMA:源MAC地址L/T:帧长LLCHeader:配置消息固定的链路头Payload:BPDU数据,Payload,L/T,SMA,DMA,LLCHeader,RootID,RootPathCost,BridgeID,PortID,Parameters,Byte,ProtocolID,2,ProtocolVersionID,BPDUType,Flags,MessageAge,1,1,1,8,4,8,2,2,MaxAge,HelloTime,ForwardDelay,2,2,2,STP介绍STP基本概念STP计算过程STP端口状态STP拓扑改变处理过程STP协议的不足,目录,计算步骤,任务一：选举根桥任务二：确定端口角色,SWBBID=8192.MACB,SWABID=0.MACA,SWDBID=4096.MACD,1GigPathCost=20,1GigPathCost=20,100MPathcost=200,100MPathcost=200,SWCBID=32768.MACC,2Gig聚合Pathcost=18,计算方法,配置BPDU处理网桥将各个端口收到的配置BPDU和自己的配置BPDU做比较，得出优先级最高的配置BPDU网桥用优先级最高的配置BPDU更新本身的配置BPDU，用于选举根桥和确定端口角色网桥从指定端口发送新的配置BPDU配置BPDU比较原则优先级向量最小者最优首先比较RootBridgeID其次比较RootPathCost再次比较DesignateBridgeID再其次比较DesignatePortID最后比较BridgePortID,根桥选举过程,SWBBID=8192.MACB,SWABID=0.MACA,SWDBID=4096.MACD,SWCBID=32768.MACC,我是根桥,我是根桥,我是根桥,寻找最小桥ID,RootID=8192.MACB,根桥选举过程（续）,RootID=8192.MACB,RootID=0.MACA,RootID=0.MACA,RootID=32768.MACC,RootID=8192.MACB,RootID=32768.MACC,RootID=32768.MACC,RootID=4096.MACD,RootID=4096.MACD,SWABID=0.MACA,SWBBID=8192.MACB,SWCBID=32768.MACC,SWDBID=4096.MACD,根桥选举过程（续）,SWBBID=8192.MACB,SWABID=0.MACA,SWDBID=4096.MACD,SWCBID=32768.MACC,我是根桥,SWA是根桥,SWA是根桥,根桥选举过程（续）,RootID=0.MACA,RootID=0.MACA,RootID=0.MACA,RootID=0.MACA,RootID=0.MACA,RootID=0.MACA,RootID=4096.MACD,RootID=4096.MACD,SWABID=0.MACA,SWBBID=8192.MACB,SWCBID=32768.MACC,SWDBID=4096.MACD,根桥选举结果,SWBBID=8192.MACB,SWABID=0.MACA,SWDBID=4096.MACD,SWCBID=32768.MACC,SWA是根桥,SWA是根桥,SWA是根桥,确定端口角色的标准,根端口：网桥上到根桥最近的端口指定端口：端口的配置BPDU在其所属链路上是最优的Alternate端口：端口的配置BPDU在其所属链路上不是最优的，且端口不是根端口,端口角色确定过程,SWBBID=8192.MACB,SWABID=0.MACA,SWDBID=4096.MACD,1GigPathCost=20,1GigPathCost=20,100MPathcost=200,100MPathcost=200,SWCBID=32768.MACC,2Gig聚合Pathcost=18,RootID=32768.MACCRPC=0,RootID=8192.MACBRPC=0,端口角色确定过程（续）,RootID=8192.MACBRPC=0,RootID=8192.MACBRPC=0,RootID=0.MACARPC=0,RootID=0.MACARPC=0,RootID=32768.MACCRPC=0,RootID=32768.MACCRPC=0,RootID=4096.MACDRPC=0,RootID=4096.MACDRPC=0,SWABID=0.MACA,SWBBID=8192.MACB,SWCBID=32768.MACC,SWDBID=4096.MACD,端口角色确定过程（续）,SWBBID=8192.MACB,SWABID=0.MACA,SWDBID=4096.MACD,SWCBID=32768.MACC,我是根桥RPC=0,我是根桥RPC=0,SWA是根桥RPC=18,RPC=200,RPC=18,SWA是根桥RPC=200,端口角色确定过程（续）,RootID=0.MACARPC=18,RootID=0.MACARPC=200,RootID=0.MACARPC=200,RootID=0.MACARPC=0,RootID=0.MACARPC=0,RootID=0.MACARPC=18,RootID=4096.MACDRPC=0,RootID=4096.MACDRPC=0,SWABID=0.MACA,SWBBID=8192.MACB,SWCBID=32768.MACC,SWDBID=4096.MACD,端口角色确定过程（续）,SWBBID=8192.MACB,SWABID=0.MACA,SWDBID=4096.MACD,SWCBID=32768.MACC,我是根桥RPC=0,SWA是根桥RPC=18,RPC=38,RPC=18,RPC=218,SWA是根桥RPC=38,SWA是根桥RPC=218,端口角色确定过程（续）,RootID=0.MACARPC=18,RootID=0.MACARPC=38,RootID=0.MACARPC=0,RootID=0.MACARPC=0,RootID=0.MACARPC=18,SWABID=0.MACA,SWBBID=8192.MACB,SWCBID=32768.MACC,SWDBID=4096.MACD,端口角色确定过程（续）,SWBBID=8192.MACB,SWABID=0.MACA,SWDBID=4096.MACD,SWCBID=32768.MACC,我是根桥RPC=0,SWA是根桥RPC=18,RPC=38,RPC=18,RPC=58,SWA是根桥RPC=38,SWA是根桥RPC=58,端口角色确定结果,Alternate端口：端口既非根端口也非指定端口,指定端口：端口拥有该链路上最优的配置消息,根桥路径开销=38,根桥ID=0.MACARootPathCost=18,根桥ID=0.MACARootPathCost=38,根桥ID=0.MACARootPathCost=0,根端口：该端口到根桥的开销最小38200,根桥路径开销=200,SWBBID=8192.MACB,STP计算结果,SWBBID=8192.MACB,SWABID=0.MACA,SWDBID=4096.MACD,SWCBID=32768.MACC,指定端口,指定端口,根端口,根端口,根端口,指定端口,指定端口,Alternate端口,Alternate端口,根桥,指定端口,等路径开销计算,根桥,SWABID=0.MACA,SWABID=0.MACA,根桥,SWBBID=8192.MACB,SWCBID=32768.MACC,SWBBID=8192.MACB,SWCBID=32768.MACC,SWDBID=4096.MACD,Pathcost=200,Pathcost=200,Pathcost=200,Pathcost=200,Pathcost=200,Pathcost=200,Pathcost=200,D,D,R,R,D,A,D,D,R,R,R,D,D,A,等路径开销计算（续）,R,Pathcost=200,Pathcost=200,SWABID=0.MACA,根桥,SWBBID=8192.MACB,E0/1,E0/2,D,D,A,R,Pathcost=200,Pathcost=200,SWABID=0.MACA,根桥,SWBBID=8192.MACB,E0/1,D,A,Pathcost=200,E0/2,E0/1,E0/1,E0/2,PhysicalSegment,收到低优先级配置BPDU时的处理,根桥,根桥,BPDU,BPDU,BPDU,SWABID=0.MACA,SWBBID=8192.MACB,SWCBID=32768.MACC,SWABID=0.MACA,SWBBID=8192.MACB,SWCBID=32768.MACC,SWDBID=4096.MACD,BPDU,低优先级配置BPDU,HelloTimer,BPDU,STP介绍STP基本概念STP计算过程STP端口状态STP拓扑改变处理过程STP协议的不足,目录,临时环路问题,当拓扑结构发生变化，新的配置BPDU要经过一定的时延才能传播到整个网络，在所有网桥收到这个变化的消息之前可能会存在临时环路,根桥,SWABID=0.MACA,SWBBID=8192.MACB,SWCBID=4096.MACC,D,R,D,R,根桥,SWABID=0.MACA,SWBBID=8192.MACB,SWCBID=4096.MACC,D,R,D,D,R,D,新链路,通过中间状态避免临时环路,STP为端口定义了五种状态：Disabled、Blocking、Listening、Learning、Forwarding各端口状态对配置BPDU收发、MAC地址学习以及数据收发的处理有所不同,ForwardDelay延时,从中间状态Listening经过一个延时进入另一个中间状态Learning从Learning状态再经过一个延时进入Forwarding状态延时长度为ForwardDelay,STP端口状态机,Disabled,Listening,Blocking,Forwarding,Learning,1）端口enabled,2）端口disabled,3）端口被选为根端口或指定端口,4）端口被选为Alternate端口（阻塞）,5）ForwardDelay延时,（1）,（2）,（2）,（2）,（2）,（1）,（2）,（4）,（4）,（5）,（4）,（5）,（3）,STP端口状态示例,SWB,SWA,SWD,SWC,Forwarding,Forwarding,Forwarding,Forwarding,Forwarding,Forwarding,Forwarding,Blocking,Blocking,根桥,Forwarding,STP介绍STP基本概念STP计算过程STP端口状态STP拓扑改变处理过程STP协议的不足,目录,E1/0/1,拓扑发生变化,HostA,HostB,ROOT,SWC,SWA,SWB,SWD,SWE,链路中断,E1/0/1,E1/0/2,E1/0/1,E1/0/2,E1/0/2,E1/0/3,E1/0/2,E1/0/1,E1/0/2,E1/0/1,从中断到恢复需要等待MAC地址老化，将近5分钟的时间！,STP阻塞,STP拓扑改变处理过程,拓扑改变消息TCN,拓扑改变应答消息TCA,拓扑改变置位的BPDU,HostA,HostB,ROOT,链路中断,E1/0/1,E1/0/2,E1/0/1,E1/0/2,E1/0/1,E1/0/2,E1/0/3,E1/0/2,E1/0/1,E1/0/2,E1/0/1,拓扑改变时网桥使用较小的MAC地址生存期从中断到恢复最长需要等待50秒的时间！,1,2,3,4,4,5,5,5,STP阻塞,SWC,SWA,SWB,SWD,SWE,TCNBPDU,Payload,L/T,SMA,DMA,LLCHeader,网桥发送TCNBPDU的条件为有端口转变为Forwarding状态，且该网桥至少包含一个指定端口有端口从Forwarding状态或Learning状态转变为Blocking状态,Parameters,Byte,ProtocolID,2,ProtocolVersionID,BPDUType,1,1,TCA以及TC置位的配置BPDU,Payload,L/T,SMA,DMA,LLCHeader,6,5,4,3,2,1,0,TopologyChange,TopologyChangeAcknowledgment,7,标志位置位第7位置位表示该消息为TCA第0位置位表示该消息为TC置位BPDU1到6位保留,标志位,RootID,RootPathCost,BridgeID,PortID,Parameters,Byte,ProtocolID,2,ProtocolVersionID,BPDUType,Flags,MessageAge,1,1,1,8,4,8,2,2,MaxAge,HelloTime,ForwardDelay,2,2,2,拓扑改变收敛时延分析,SWABID=0.MACA,SWBBID=8192.MACB,SWCBID=32768.MACC,D,D,R,R,D,A,根桥故障,BPDU,等待MaxAgeTimer,链路中断,SWABID=0.MACA,SWBBID=8192.MACB,SWCBID=32768.MACC,D,D,R,R,D,A,SWC根端口DOWN,BPDU,BPDU,BPDU,拓扑改变收敛时延分析（续）,ROOT,SWC,SWA,SWB,SWD,SWE,E1/0/1,E1/0/1,E1/0/2,E1/0/1,E1/0/3,E1/0/2,E1/0/1,E1/0/2,E1/0/1,E1/0/2,新增链路或故障恢复链路,新阻塞链路,STP介绍STP基本概念STP计算过程STP端口状态STP拓扑改变处理过程STP协议的不足,目录,收敛时间长,PowerUp,Blocking,Listening,Learning,Forwarding,Disabled,ForwardDelayTimer,ForwardDelayTimer,缺省情况下一个端口从Blocking状态过渡到Forwarding状态至少需要30秒钟（两倍的ForwardDelay）。对于一个拓扑不稳定网络，会导致网络的长时间中断,拓扑变化收敛机制不灵活,ROOT,SWC,SWA,SWB,SWD,SWE,E1/0/1,E1/0/2,E1/0/1,E1/0/2,E1/0/1,E1/0/2,E1/0/3,E1/0/2,E1/0/1,E1/0/2,E1/0/1,STP阻塞,主机频繁上下线时，网络会产生大量TCN,Page54,LANE,SWA,LANA,LANB,LANC,SWB,SWC,LAND,Root,LANC的指定端口,E0/10,E0/20,E0/10,E0/20,E0/10,E0/20,STP基本配置物理拓扑,Page55,STP基本配置配置命令,LANE,SWA,LANA,LANB,LANC,SWB,SWC,LAND,Root,LANC的指定端口,E0/10,E0/20,E0/10,E0/20,E0/10,E0/20,QuidwaysysnameSWASWAstpenableSWAstpmodestpSWAstppriority4096,QuidwaysysnameSWBSWBstpenableSWBstpmodestpSWBstppriority8192,QuidwaysysnameSWCSWCstpenableSWCstpmodestp,E0/24,Page56,SWCdisplaystp-CISTGlobalInfoModeSTP-CISTBridge:32768.00e0-fc41-43b9BridgeTimes:Hello2sMaxAge20sFwDly15sMaxHop20CISTRoot/ERPC:4096.00e0-fc41-42