Failure of the link to be established
Poor performance of the link during regular usage
Problems that can be traced to the networks on either side of the link
The easiest way to find out if PPP works is to run a command over the link. Run a command such as ping or traceroute to a host on the peer's network. Then observe the results. However, you should use PPP and UNIX debugging tools to monitor performance of an established link or to troubleshoot a problematic link.
This section explains how to obtain diagnostic information from pppd and its associated log files. The remaining sections in this chapter describe common problems with PPP that you can discover and fix with the aid of the PPP troubleshooting tools.