2. 计算机
  3. Refer to the exhibit． Each of these four switches has been configured with a hostname, as well as being configured to run RSTP．

Refer to the exhibit． Each of these four switches has been configured with a hostname, as well as being configured to run RSTP．

admin2019-04-08  0
问题 Refer to the exhibit． Each of these four switches has been configured with a hostname, as well as being configured to run RSTP． No other configuration changes have been made． Which three of these show the correct RSTP port roles for the indicated switches and interfaces?
选项 A、        SwitchA, Fa0/2, designated
B、        SwitchA, Fa0/1, root
C、        SwitchB, Gi0/2, root
D、        SwitchB, Gi0/1, designated
E、        SwitchD, Gi0/2, root
答案A,B,E
解析 如图，每个交换机都配置了主机名，也都运行了RSTP，在就没有做其他的配置了。下面哪三个选项正确的描述了RSTP的端口角色？
考点分析：
1．判断根桥，通过比较各个网桥的Mac地址，桥Mac地址最小的为根桥，所以根桥是C，根桥上的所有端口是指定端口。
2．判断非根桥上的跟端口。在同一个交换机上，到根网桥的cost较小的那个端口会成为root port。所以SwitchA Fa0/1，SwitchD Gi0/2，SwitchB Gi0/1会成为相应交换机上的RP。
3．判断每个网段上的指定端口。 SWA--SWB段：SWA的F0/2端口的cost为19，SWB的G0/2端口cost为4+19=23，所以SWA的F0/2为指定端口。 SWB--SWD段：SWB的G0/1端口cost为19+19=38，SWD的G0/1端口cost为19，所以SWD的G0/1端口为指定端口。
4．剩余SWB的G0/2端口既不是指定端口，又不是根端口，处于堵塞状态。
注：100M链路cost为19．1000M链路cost为4．
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