5、STP实验指导 (TEST系列文档) V1.1

STP 实验指导Version 1.1 update：2014-09-09 By：鲍中帅一、概述 (2)二、实现 (2)2.1、实现前提 (2)2.2、具体步骤 (2)2.3、手工控制 (4)三、补充 (6)一、概述在二层网络中，常常考虑到冗余链路或者由于人为失误导致在两台二层设备之间存在多条物理链路，而根据交换机工作原理，对于组播帧、广播帧以及未知单播帧采取泛洪的处理方式，这就导致了在二层以太网中极其容易出现数据帧被重复、来回传递；当二层冗余链路过多时，极其容易出现所谓的“广播风暴”，这将给网络设备以及链路带来比较大的负载；所以，需要在二层有消除环路的协议，这就是今天的主角：STP(Spanning Tree Protocol)；STP是一款能够在数据链路层消除物理环路的协议；主要功能有两个：1、阻断冗余链路；2、当可用链路发生故障时，恢复被阻断的冗余链路，提高网络可用性；本实验的目标：利用STP协议，消除二层设备之间的环路；二、实现2.1、实现前提默认情况下，在H3C的交换机中，STP是处于关闭状态的；所以需要手工开启；2.2、具体步骤#默认情况下，STP处于关闭状态；[SW2]display stpProtocol Status :disabledProtocol Std. :IEEE 802.1sVersion :3CIST Bridge-Prio. :32768MAC address :000f-e25f-ae42Max age(s) :20Forward delay(s) :15Hello time(s) :2Max hops :20#开启STP；[Switch]stp enable#开启后；[SW2]display stp-------[CIST Global Info][Mode MSTP]-------//默认情况下，STP的版本为MSTP；CIST Bridge :32768.0cda-417d-1d63Bridge Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20CIST Root/ERPC :32768.000f-e25f-ae42 / 200CIST RegRoot/IRPC :32768.0cda-417d-1d63 / 0CIST RootPortId :128.1BPDU-Protection :disabledBridge Config-Digest-Snooping :disabledTC or TCN received :129Time since last TC :0 days 0h:0m:33s#通过命令可以查看到哪些接口被阻塞；E1/0/10被阻塞；证明，当网络中存在冗余链路时，会在逻辑上阻塞冗余链路，防止网络发生环路；需要留意的是，阻塞是逻辑上的，通过查看交换机指示灯，被阻塞接口的指示灯仍然是点亮的状态；[SW2]dis stp briefMSTID Port Role STP State Protection0 Ethernet1/0/1 ROOT FORWARDING NONE0 Ethernet1/0/10 ALTE DISCARDING NONE[SW2]display stp interface e1/0/1----[CIST][Port1(Ethernet1/0/1)][FORWARDING]----Port Protocol :enabledPort Role :CIST Root PortPort Priority :128Port Cost(Legacy) :Config=auto / Active=200Desg. Bridge/Port :32768.000f-e25f-ae42 / 128.1Port Edged :Config=disabled / Active=disabledPoint-to-point :Config=auto / Active=trueTransmit Limit :10 packets/hello-timeProtection Type :NoneMST BPDU Format :Config=auto / Active=legacyPort Config-Digest-Snooping :disabledNum of Vlans Mapped :1PortTimes :Hello 2s MaxAge 20s FwDly 15s MsgAge 0s RemHop 20BPDU Sent :3TCN: 0, Config: 0, RST: 0, MST: 3BPDU Received :39TCN: 0, Config: 0, RST: 0, MST: 39TCN: 0, Config: 0, RST: 0, MST: 39[SW2]display stp interface e1/0/10----[CIST][Port10(Ethernet1/0/10)][DISCARDING]----Port Protocol :enabledPort Role :CIST Alternate PortPort Priority :128Port Cost(Legacy) :Config=auto / Active=200Desg. Bridge/Port :32768.000f-e25f-ae42 / 128.10Port Edged :Config=disabled / Active=disabledPoint-to-point :Config=auto / Active=trueTransmit Limit :10 packets/hello-timeProtection Type :NoneMST BPDU Format :Config=auto / Active=legacyPort Config-Digest-Snooping :disabledNum of Vlans Mapped :1PortTimes :Hello 2s MaxAge 20s FwDly 15s MsgAge 0s RemHop 20BPDU Sent :20TCN: 0, Config: 0, RST: 0, MST: 20BPDU Received :106TCN: 0, Config: 0, RST: 0, MST: 106#当可用链路E1/0/1口发生故障时，先前被阻塞的链路会恢复转发状态；例如，将E1/0/1口拔出，E1/0/10口恢复转发；[SW2]dis stp briefMSTID Port Role STP State Protection0 Ethernet1/0/10 ROOT FORWARDING NONE2.3、手工控制#另外，我们也可以手工控制根桥的位置；从而控制被阻塞接口的位置；通过命令行实现；[SW2]stp root primary //设置当前根桥为主根桥；[SW2]display stp briefMSTID Port Role STP State Protection0 Ethernet1/0/1 DESI FORWARDING NONE0 Ethernet1/0/10 DESI FORWARDING NONE#可以看到，将SW2设置为根桥后，SW2上就没有阻塞端口了，此时的阻塞端口已经转移到了SW1设备上；[SW2]display stp-------[CIST Global Info][Mode MSTP]-------CIST Bridge :0.0cda-417d-1d63Bridge Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20CIST Root/ERPC :0.0cda-417d-1d63 / 0CIST RegRoot/IRPC :0.0cda-417d-1d63 / 0CIST RootPortId :0.0BPDU-Protection :disabledBridge Config-Digest-Snooping :disabledCIST Root Type :PRIMARY rootTC or TCN received :129Time since last TC :0 days 0h:0m:17s[SW1]display stp-------[CIST Global Info][Mode MSTP]-------CIST Bridge :32768.000f-e25f-ae42Bridge Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20CIST Root/ERPC :0.0cda-417d-1d63 / 200CIST RegRoot/IRPC :32768.000f-e25f-ae42 / 0CIST RootPortId :128.1BPDU-Protection :disabledTC-Protection :enabled / Threshold=6Bridge ConfigDigest Snooping :disabledTC or TCN received :7Time since last TC :0 days 0h:0m:39s#通过对比可以看到，SW1的桥ID没有SW2的桥ID优，因此网络中的根桥为SW2；#我们还可以将一个接口关闭STP协议；[SW1-Ethernet1/0/11]stp disable //关闭接口上的STP；[SW1-Ethernet1/0/11]display stp interface e1/0/10----[CIST][Port10(Ethernet1/0/10)][DISABLED]----//接口STP被关闭，状态为disabled；Port Protocol :disabled#通常情况下，为了加快连接PC端口的STP状态迁移，都会将这类接口设置为边缘端口；[SW1-Ethernet1/0/12]stp edged-port enable //将此接口设置为边缘接口；[SW1-Ethernet1/0/12]display stp interface e1/0/12----[CIST][Port10(Ethernet1/0/12)][FORWARDING]----Port Protocol :enabledPort Role :CIST Designated PortPort Priority :128Port Cost(Legacy) :Config=auto / Active=200Desg. Bridge/Port :32768.000f-e25f-ae42 / 128.10Port Edged :Config=enabled / Active=enabled //开启成功；Point-to-point :Config=auto / Active=trueTransmit Limit :10 packets/hello-timeProtection Type :NoneMSTP BPDU format :Config=auto / Active=legacyPort ConfigDigest Snooping :disabledRapid Fwd State :Rapid ForwardingNum of Vlans Mapped :1PortTimes :Hello 2s MaxAge 20s FwDly 15s MsgAge 1s RemHop 20BPDU Sent :2TCN: 0, Config: 2, RST: 0, MST: 0BPDU Received :0TCN: 0, Config: 0, RST: 0, MST: 0三、补充关于在接口下stp disable与stp edged-port enable两个的区别：1、stp disable后，这个接口不参与STP计算，即使这个接口再接收到STP BPDU后也只会当作普通的组播帧泛洪，此时容易发生环路；因此慎用stp disable；2、stp edged-port enable后，此接口一旦up，就立刻Forwarding状态，收敛速度极快，这一点上和stp disable此端口效果一致；但区别是edged-port后，此端口再接收到STP BPDU时，会丧失快速收敛的属性，变成普通端口，并参与STP的计算，这时，对比stp disable的优势就提现出来；3、最后，需要指出的是，stp disable后，STP BPDU不会从这个接口主动定时发送出去；但stpedged-port enable后，此端口仍然会主动定时向外发送STP BPDU；。