Network Troubleshooting

What it is

Network troubleshooting is the systematic process of isolating which layer and which hop a connectivity problem lives at — the practical, applied counterpart to understanding the OSI/TCP-IP layers and how traffic actually flows.

Key points

• Layer-by-layer isolation: working from the physical/link layer up (is the interface up, is there an IP address, can I reach the gateway, can I resolve DNS, can I reach the destination) narrows the problem systematically instead of guessing at causes.
• Standard tools: ping tests basic reachability, traceroute/tracert shows the path (and where along it connectivity breaks), and dig/nslookup diagnoses DNS-specific issues — each tool maps to isolating a specific layer.
• Distinguishing "down" from "slow": a complete outage and severe latency have very different causes and troubleshooting paths — conflating them wastes time investigating the wrong thing.
• The core discipline is forming a hypothesis about where in the path the problem is, then testing that specific hypothesis — rather than randomly trying fixes without first localizing where the actual failure is.