Guides to networks, passwords, time and image formats
Each guide explains the idea behind one of the tools: what the numbers mean, the rules that catch people out, and what is worth checking. They are checked against the published standards and updated when those change.
Networks
- IP addresses explained: IPv4, IPv6 and the reserved rangesWhy there are two kinds of address, why a website sees only one of yours, and the ranges that never appear on the public internet.
- DNS records explained: A, AAAA, CNAME, MX, TXT and NSHow a name becomes an address, what each common record type holds, and why a change can take hours to reach everyone.
- Subnets and CIDR explained: prefixes, masks and usable hostsWhat the number after the slash means, how many hosts each prefix holds, and how to split one network into several.