DNS & Domains
How domain names resolve: record types, nameservers, TTLs and caching, DNSSEC, encrypted DNS, and the SPF, DKIM and DMARC records behind email.
Beginner
2 guidesDNS record types explained: A, CNAME, MX, TXT and more
What A, AAAA, CNAME, MX, TXT, NS, SOA, CAA, SRV, PTR and HTTPS records do. Each comes with a zone file example, and the CNAME rule is stated exactly.
Domain name structure: registries, registrars and DNS hosts
How domain names are built from labels, what the registry, registrar and DNS host each do, how delegation works, and why a CNAME cannot sit at the apex.
Intermediate
5 guidesHow DNS resolution works, step by step
The path of one DNS lookup through browser and OS caches, a recursive resolver, and root, TLD and authoritative servers, and how to watch it with dig +trace.
DNS TTL and caching: why DNS changes take time
How DNS TTL controls caching, why DNS propagation means waiting for caches to expire, how to lower the TTL before a change, and how negative answers are cached.
DNS over HTTPS vs DNS over TLS: what each one hides
DoH and DoT both encrypt DNS between your device and a resolver. How they differ, what they hide, what they still reveal, and the network-filtering trade-off.
How to troubleshoot DNS: NXDOMAIN, SERVFAIL and more
Diagnose DNS problems by response code: causes and fixes for NXDOMAIN, SERVFAIL, REFUSED and stale answers, with the dig and nslookup commands to run.
SPF, DKIM and DMARC: how email authentication works
What SPF, DKIM and DMARC each prove, how DMARC alignment ties them to the visible From address, example records, and a safe order to roll them out.
Tools for this topic
Try what these guides describe on your own URLs, domains, code or files.
Look up a domain's records on Cloudflare, Google or Quad9 and switch resolvers to compare their answers.
Count an SPF record's DNS lookups, generate a DMARC record, and check a DKIM selector you enter.
Check SPF, DMARC, MX, a DKIM selector, MTA-STS and TLS-RPT against a sender-requirements checklist (sign-in required).