In this section, I have tried to assemble a compendium of software tools for testing various aspects of Internet operation.
Ping performs the most fundamental tests of network operation.
TraceRoute can help diagnose routing problems. TCPdump was designed to study TCP operation, but can also be used as a generic packet analyzer. The real trick of successful network troubleshooters is this - they understand the protocols and design well enough to know what should be happening in any given instance. That doesn't mean memorizing all the RFCs, but you need to know where to go to get information when you need it. Once you know what should be happening, break it down into simpler steps or components.