6.2. Cabling and Physical Interface Issues

💡 First Principle: Physical layer problems cause symptoms at every layer above—a bad cable looks like a routing problem because packets don't arrive. Always verify Layer 1 first: if bits can't traverse the wire, nothing else matters.

Think of physical troubleshooting like checking if a lamp is plugged in before replacing the bulb. It's obvious in retrospect but easy to skip when focused on complex configurations.

Why this matters for troubleshooting: Technicians waste hours chasing VLAN configurations or routing tables when a crimped cable or dirty fiber connector is the actual culprit. Start at Layer 1, and you'll resolve issues faster.