Testing Basic Connectivity
The ping command tests whether a remote host can be reached from your computer. This simple function is extremely useful for testing the network connection, independent of the application in which the original problem was detected. ping allows you to determine whether further testing should be directed toward the network connection (the lower layers) or the application (the upper layers). If ping shows that packets can travel to the remote system and back, the user’s problem is probably in the upper layers. If packets can’t make the round-trip, lower protocol layers are probably at fault.
Frequently, a user reports a network problem by stating that he can’t Telnet (or FTP, or send email, or whatever) to some remote host. He then immediately qualifies this statement with the announcement that it worked before. In cases like this, where the ability to connect to the remote host is in question, ping is a very useful tool.
Using the host name provided by the user, ping the remote host. If your ping is successful, have the user ping the host. If the user’s ping is also successful, concentrate your further analysis on the specific application that the user is having trouble with. Perhaps the user is attempting to Telnet to a host that only provides anonymous FTP. Perhaps the host was down when the user tried his application. Have the user try it again, while you watch or listen to every detail of what he or she is doing. If he is doing everything right and the ...