Systematic Troubleshooting

The real power of the OSI Model is using it as a troubleshooting framework. Start at Layer 1 and work your way up, verifying each layer before moving to the next.

The method:

1. Layer 1 — Physically connected? Link light on?
2. Layer 2 — MAC in switch table? Correct VLAN?
3. Layer 3 — Has IP address? Can ping gateway?
4. Layer 4 — Application connecting on correct port?

The Framework Applied

“Where is it coming from, where do I want it to go?” — walking through the layers answers this question systematically.