CCNA640-802题库解析–常见接口网络故障分析
本文主要讲解的是使用分层模型分析常见的接口网络故障。
The show interfaces serial 0/0 command resulted in the output shown in the graphic. What are possible causes for this interface status? (Choose three.）
A:The interface is shut down.
B:No keepalive messages are received.
C:The clockrate is not set.
D:No loopback address is set.
E:No cable is attached to the interface.
F:There is a mismatch in the encapsulation type.
Correct Answers:B, C, F
show interfaces用来查看路由器配置的接口状态，由图示串行接口的状态为一个up一个down，前者是物理层，后者是数据链路层，出现的可能的情况有：(1)没有收到keeplive的报文；（2）接口的时钟频率没有设置；（3）接口封装不匹配。这些都有可能导致接口的数据链路层为down的。
Refer to the exhibit. Hosts innetwork192.168.2.0 are unable to reach hosts in network 192.168.3.0. Based on the output from RouterA, what are two possible reasons for the failure? (Choose two.)
A:The cable that is connected to S0/0 on RouterA is faulty.
B:Interface S0/0 on RouterB is administratively down.
C:Interface S0/0 on RouterA is configured with an incorrect subnet mask.
D:The IP address that is configured on S0/0 of RouterB is not in the correct subnet.
E:Interface S0/0 on RouterA is not receiving a clock signal from the CSU/DSU.
F:The encapsulation that is configured on S0/0 of RouterB does not match the encapsulation that is configured on S0/0 of RouterA.
Correct Answers:E, F
show ip interfaces brief命令用来显示路由器配置的所有接口线路，协议以及IP信息等状态。同上面的解析一样，串行接口的状态为一个up一个down，前者是物理层，后者是数据链路层，出现的可能的情况有：(1)没有收到keeplive的报文；（2）接口的时钟频率没有设置；（3）接口封装不匹配。这些都有可能导致接口的数据链路层为down的。S0/0的链路层down掉了，很明显E，F是可能出现的情况。
Refer to the exhibit. The network administrator has verified that a functioning cable connects Switch1 and Switch2. From the output that is shown, what two pieces of information can the administrator validly conclude? (Choose two.)
A:Using a source MAC address of 0009.11f3.8848, Switch2 is sending frames to Switch1.
B:Interface fa0/1 on Switch1 is in a shutdown state.
C:The status of fa0/2 should be checked on Switch2.
D:There is likely to be an IP address issue on Switch1 fa0/1.
E:The interface is functional at OSI Layer 1.
通过show interface命令看到switch1接口链路层显示的notconnect，当然需要检查对端的switch2接口的状态了，有可能物理线路都是不通的。因为它只有物理层是up的，链路层down掉了，所以我们只能说他工作在OSI的第一层。因此答案是C和E了。
Refer to the exhibit. A network administrator attempts to ping Host2 from Host1 and receives the results that are shown. What is a possible problem?
A: The link between Host1 and Switch1 is down.
B: TCP/IP is not functioning on Host1
C: The link between Router1 and Router2 is down.
D: The default gateway on Host1 is incorrect.
E: Interface Fa0/0 on Router1 is shutdown.
F: The link between Switch1 and Router1 is down.
Correct Answers:C
主机1ping主机2，显示收到Router 1回复的目的网段主机不可达的ICMP包，说明主机1和Router1之间是可以通的，但数据包发到Route1的f0/0口就被丢弃了，网络故障出在Router 1的s0/0口上，导致Route 1和Route2之间的链路down掉。很明显了，C是正确的。（关于Ping命令会在以后的专题里结合其它一些常用的网络命令做详解）
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