From Wire to DNS: A Structured Diagnostic Flow

A layered methodology for diagnosing Linux network issues by isolating failures from physical connectivity through name resolution. This is not a command guide. It is a system model.

1. Core Principle

Network problems are rarely “the internet.” They are almost always a failure at a specific layer. The key to stable troubleshooting is disciplined isolation.

2. The Layer Model

Physical — Cable, RF signal, NIC hardware
Link — Speed, duplex, association, MAC learning
IP Connectivity — Routing, gateway reachability
DNS — Name resolution services
Application — Browser, SSH, API client

Diagnose in order. Never skip layers.

3. Isolation Strategy

Change one variable at a time
Compare wired vs wireless
Compare two devices on same network
Separate raw IP reachability from DNS

4. Instrumentation by Layer

Physical / Link

ethtool eth0
iw dev wlan0 link

IP Connectivity

ping -c 5 1.1.1.1

DNS

ping -c 5 google.com
getent hosts google.com

Truth Observation

tcpdump -e -i eth0

5. Router & Infrastructure Checks

Reboot modem first, router second
Inspect router logs for WAN drops
Check Wi‑Fi channel stability
Verify DHCP assignments

6. Architectural Philosophy

Never debug “the internet.” Debug the layer.

Systems stability emerges from structured thinking, not reactive command use. Tools serve the model — not the other way around.