问题
Which command can verify Application Layer connectivity between 2 hosts?
A. arp
B. ping
C. telnet
D traceroute
E. plp
题目意思：以下命令当中那个是在应用层验证两个主机的联通性的命令？
Telnet tests the Application layer, ping test the Network layer.Telnet is an application used to remotely configure a device. If telnet is succesfful you know that full 7 layer stack on the sending and receiving host are configured correctly and are in working order
因为telnet命令是工作在应用层，ping命令是工作在网络层的，telnet是应用于远程控制设备的，所以如果能telnet成功的话，这就证明了两台主机或设备已经联通了，在联通性上面已经没有问题了。
该题目主要考学员命令工作的层面，和OSI七层的关系。
正确答案：C
