Before You tcpdump, Ask These Three Things
This column collects first-line actions for three classes of failures: down, slow, and unresolvable. Not "TCP three-way handshake explained" — that's Wikipedia's job. We write: after dig +short returns a CNAME, what's next. After tcpdump shows a RST, where to look.
Contents (7 posts)
| Slug | Value | Keyword |
|---|---|---|
| [tcp-ip](tcp-ip.md | Understand TCP from state machine, read ss / netstat |
TCP/IP state machine |
| [tcp-troubleshoot](tcp-troubleshoot.md | TIME_WAIT / RST / SYN half-open / retransmission | TCP troubleshooting |
| [dns-resolution](dns-resolution.md | Recursive / iterative / caching full flow | DNS resolution |
| [dns-troubleshoot](dns-troubleshoot.md | dig / host / nslookup — which to use when | DNS troubleshooting |
| [cdn-principles](cdn-principles.md | Origin fetch, preheat, cache invalidation | CDN origin & cache |
| [nginx-proxy](nginx-proxy.md | 502 / 504 / location matching decision tree ⭐ | Nginx reverse proxy |
| [wireshark-basics](wireshark-basics.md | 30 common filters + field cheat sheet | Wireshark filters |
Launch Flagship
[Nginx Reverse Proxy 502/504 Troubleshooting](nginx-proxy.md ⭐ W1 flagship
Nginx 502/504 is the highest-frequency ops error. This post walks through upstream probing, location matching priority, proxy_read_timeout, SSL cert chain — with a decision tree.
Tags
nginxreverse-proxy502tcpdnscdnwiresharktroubleshoot