問題
which command can verify application layer connectivity between 2 hosts?
a. arp
b. ping
c. telnet
d traceroute
e. plp
題目意思：以下命令當中那個是在套用層驗證兩個主機的聯通性的命令？
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
因為telnet命令是工作在套用層，ping命令是工作在網路層的，telnet是套用於遠程控制設備的，所以如果能telnet成功的話，這就證明了兩台主機或設備已經聯通了，在聯通性上面已經沒有問題了。
該題目主要考學員命令工作的層面，和osi七層的關係。
正確答案：c