军哥整理网工数通STP面试题

乾颐堂 · 发表于 2022-10-10 13:28:11

实验总结

STP作用：破环，冗余
BPDU = Bridge Protocol Data Unit 桥协议数据单元，包含STP详细信息，交换机每两秒发送一次
BID = Bridge ID,桥ID，交换机的“身份证”，由优先级（默认32768,最小为0，必须是4096倍数） + MAC 组成
Root 根桥【整个交换网络中有且只有1个】，选出STP生成树的参考点。比较桥ID，越小优先级越高；通过指定优先级来确认主根、备根。通过同化、转发BPDU ，
RootPort，RP，根端口（不需要人为设置，自动选择，可以正常收发数据帧）。所有非根交换机确认一个RP；Root选举完毕后，非根交换机选择一个RP根端口（本质是一个距离根桥更近的端口）。
RP端口的确认依据： RPC RootPortCost 根路径开销：交换机的每个端口都有一个开销值与端口的速率有关，反比，速率越高开销越小【G口千M=开销20000】。发送BPDU的桥ID【优先级+MAC】：越小越优。发送者的Port ID，端口ID，PID【优先级（默认128）+端口号】：越小越优。接收者的端口ID，越小越优
DP端口，指定端口 Designated Port：RP端口选举完后基于每条链路确认DP端口，可以正常收数据帧，本质也是离根桥最近的端口【通常，根桥交换机接口都是DP端口】。选举依据：RPC、发送者的BID、发送者的PID。
STP经过选举 Root、RP、DP后，剩下的端口为AP端口 Alternate Port即堵塞备用替代端口，逻辑上堵塞，避免成环。
STP的五种端口状态

　　　　Disabled    禁用    不运行STP
　　　　Blocking    阻塞    只接受STP BPDU，不发送STP BPDU，不学习MAC，不转发用户数据-----AP端口状态
　　　　Listening    侦听    接受、转发STP BPDU，不学习MAC，不转发用户数据    15s
　　　　Learning    学习    接受、转发STP BPDU，学习MAC，不转发用户数据    15s
　　　　Forwarding  转发    接受、转发STP BPDU，学习MAC，转发用户数据
　　状态转变时间
　　　　阻塞  →  侦听    0s~20s时间
　　　　侦听  →  学习    15s时间
　　　　学习  →  转发    15s时间
端口的三种角色：RP、DP、AP，端口的角色转换【拓扑发生变化】和状态转换没有必然联系。
通过设置边缘端口【一般直接与终端设备直连】来避免因为端口状态转变耗费的时间增加了等待时间，disable直接变为forwaing
接口下开启关闭边缘端口：  stp edged-port enable / disable
接口优先级高于全局优先级，可先在接口下关闭边缘端口，在从全局模式下开启边缘端口【stp edged-port default】
实验目地

STP生成树协议配置，端口选举规则，边缘端口

实验现象

交换机每两秒发送一次 BPDU
交换机桥ID和Root根桥
RP端口
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- 关键命令
- display stp 查看交换机生成树信息
# 查看交换机生成树信息<Huawei>dis stp-------[CIST Global Info][Mode MSTP]-------CIST Bridge :32768.4c1f-cca3-1f5cConfig Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20Active Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20CIST Root/ERPC :32768.4c1f-cc6f-7f25 / 20000
- stp priority num 设置stp 桥ID的优先级【0-32768，必须是4096倍数】
- stp root primary 主根【优先级0】，stp root secondary 备份根【优先级4096】
- dis stp brief 查看 STP 简要信息， stp edged-port enable 端口下开启边缘端口
# 设置stp 桥ID的优先级[S1]stp priority 0[S1]dis stp-------[CIST Global Info][Mode MSTP]-------CIST Bridge :0 .4c1f-cca3-1f5cConfig Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20Active Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20CIST Root/ERPC :0 .4c1f-cca3-1f5c / 0[S1]stp root ? primary Primary root switch secondary Secondary root switch[S1]stp root primary [S1]stp root secondary [S3]dis stp brief MSTID Port Role STP State Protection 0 GigabitEthernet0/0/1 ROOT FORWARDING NONE 0 GigabitEthernet0/0/2 ALTE DISCARDING NONE[S3]# LSW3[Huawei-GigabitEthernet0/0/20]stp edged-port enable# LSW9[Huawei-GigabitEthernet0/0/1]stp edged-port enable
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