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Network Troubleshooting: OSI-Layer Methodology

Beginner

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Troubleshooting methodology: start at Layer 1

Network problems can occur at any OSI layer. The most effective approach: start at the bottom (Layer 1) and work up. Confirm physical connectivity before investigating IP configuration. Confirm IP before investigating DNS. This prevents spending 30 minutes debugging DNS when the cable is simply disconnected.

'Divide and conquer' is the secondary technique: can you reach the default gateway? Can you reach a known IP? Can you resolve DNS? Each answer narrows the problem to a specific layer.

Packets in motion — click to inspect:

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