Troubleshooting Networks

A calm, methodical way to debug 'the internet is broken' - work up the layers (link, IP, gateway, DNS, destination), then use ping, traceroute, dig, and a packet capture to read exactly where the conversation died.

1. Work Up the Layers Instead of guessing, ask one yes/no question per rung - link up? have an IP? reach the gateway? resolve a name? reach the destination? - and the first 'no' is your answer.
2. The Core Tools ping tells you reachability and latency, traceroute/tracert shows the path and where it dies, and dig/nslookup answers 'is it DNS?' - here's how to read what each one's output actually means.
3. Reading a Packet Capture A packet capture is every packet on the wire, in order; learn to read the handshake, retransmissions, resets, and which side went quiet - so you can pinpoint exactly where a conversation broke.