Guides
The tools on this site tell you what something is. These pages explain what it means, and what to do next. Written for the moment when something is broken and you need an answer rather than a tutorial.
Information:
Shown in English
This guide has not been translated into your language yet, so you are reading the English original. The rest of the site stays in the language you chose.
When something is broken
Start here when it is already failing and you need to narrow it down.
- How to read traceroute outputMost of what looks alarming in a traceroute is normal. Here is which parts actually indicate a fault and which are artefacts of how the tool works.Updated 2026年9月21日
- A checking order for when the connection is badWork outward from your own machine instead of guessing. Six checks in order, each one ruling out a layer, so you stop at the first that fails.Updated 2026年9月21日
- How to report a network problem so it gets fixedWhat to put in a message to IT support or your provider so the first reply is a fix rather than a question — with a template to copy.Updated 2026年9月25日
- Certificate errors, explainedWhat “Your connection is not private” and its cousins actually mean, how to tell whether the problem is yours or the site’s, and how each one is fixed.Updated 2026年9月26日
- Fixing slow or patchy Wi-FiHow to tell a Wi-Fi problem from a line problem, and the fixes that actually help — placement, bands, channels, the device itself — in the order worth trying.Updated 2026年9月26日
Names and DNS
Why a name resolves, why it stopped, and why it is different for you.
- You changed a DNS record and nothing happenedWhy a DNS change takes effect for other people before it does for you, what TTL actually controls, and how to tell a slow change from a wrong one.Updated 2026年9月21日
- Why your email goes to spamThe causes in the order worth checking them — authentication first, then the sending server, then the message itself — and how to read the verdict a receiver already wrote into your mail.Updated 2026年9月25日
Foundations
The ideas the rest of it rests on. Worth ten minutes once.
- Private and public IP addresses, and why they differWhy the address on your laptop is not the address websites see, which ranges are private, and what that means when you try to reach something.Updated 2026年9月21日
- What your IP address reveals, and what it does notYour IP address tells a website your provider and roughly where you are. It does not tell them who you are or where you live. Here is exactly where the line sits.Updated 2026年9月25日
- Subnet masks in five minutesWhat 255.255.255.0 and /24 actually mean, the one piece of arithmetic that makes subnets easy, and why a wrong mask breaks a network in confusing ways.Updated 2026年9月25日
- IPv6 for people who already know IPv4The six differences that actually change how you troubleshoot — no NAT, several addresses per device, /64 everywhere, and why blocking ICMP breaks it.Updated 2026年9月25日
- NAT and port forwarding, without the jargonWhy everything in your home shares one address, why connections from outside cannot find your devices, and how to open a way in safely — or why you sometimes cannot.Updated 2026年9月26日
- What a VPN does, and what it does notA plain account of what a VPN hides, who can still see what, how it leaks, and how to check that yours is working.Updated 2026年9月26日
Reference
Tables to look something up in rather than read through.