The Art of the Fix - Troubleshooting & Problem-Solving

2) Thinking in Layers: Applying Troubleshooting Logic

"Thinking in Layers" is a practical way to apply the troubleshooting methodology, especially when establishing a theory (Step 2). It involves systematically checking for problems at different levels of a system, usually starting from the most basic physical layer and moving up to the most complex software layer. This prevents you from wasting time on complex software issues when the real problem is a simple disconnected cable. The OSI model for networking is a formal version of this concept.

A common layered approach looks like this:

1. Layer 1: The Physical Layer - Is it plugged in? Always start here. This layer includes anything you can physically touch.

   • Questions: Is there power? Are the cables securely connected at both ends? Are there any visible signs of damage? Are indicator lights on?

2. Layer 2: The Connectivity/Network Layer - Can it talk to anything? If the physical connections are good, check if the device can communicate with its immediate network.

   • Questions: Does it have a valid IP address? Can it ping the router (default gateway)? Can it see other devices on the local network? Is the Wi-Fi connected?

3. Layer 3: The System/OS Layer - Is the operating system healthy? Here, you investigate the health of the core software that runs the machine.

   • Questions: Has the computer been rebooted recently? Are the necessary drivers installed and up to date? Are essential system services running? Are there any error messages in the system logs (Event Viewer)?

4. Layer 4: The Application Layer - Is a specific program misbehaving? If the OS seems fine, the problem might be with a single piece of software.

   • Questions: Is it only one application that's failing? Can other applications perform a similar function? Has the application been recently updated or reconfigured?

5. Layer 5: The User Layer - Is it user error? Sometimes, the system is working perfectly, but the user is not performing the correct steps.

   • Questions: Can the user show you exactly what they are doing? Are they following the correct procedure? Is there a misunderstanding of how the software is supposed to work?

By systematically moving through these layers, you can efficiently narrow down the possibilities and pinpoint the source of the problem.