What is it?
Computers find each other by IP address. People type names like
example.com. DNS — the Domain Name System — is the worldwide phonebook
that translates the second into the first. When you press Enter, the
browser asks DNS, gets an IP, and only then can it open a connection.
Why it matters
DNS is invisible until it breaks. When it does, the page won't load and the error message is useless. Knowing how lookups work — and that they're cached — turns a vague outage into "TTL expired, propagation will take an hour" and tells you what to do next.
What to learn
- The lookup chain: resolver → root → TLD → authoritative
- Common record types: A, AAAA, CNAME, MX, TXT
- TTL and why DNS changes don't take effect immediately
- The hosts file as a local override
- DNS over HTTPS at a high level
- How a registrar, a nameserver, and a host fit together
Common pitfall
Changing a DNS record and refreshing the page. Records are cached at every
level — your machine, your router, your ISP, the resolver. The change is
real, but you might see the old answer for hours. Use a tool like
dig +trace or dnschecker.org to verify.
Resources
Primary (free):
- Cloudflare — What is DNS? · article
- MDN — DNS · docs
- How DNS works — comic · article
Practice
Pick a website you use daily. From the terminal, run dig example.com
(swap in the real domain) and read every section of the output. Identify
the record type, the TTL, and the authoritative nameserver. Done when you
can explain each line to a teammate.
Outcomes
- Walk through a DNS lookup from typed URL to TCP connection.
- Pick the right DNS record type for a given task (subdomain, mail, verification).
- Explain why a DNS change might take time to propagate.
- Use
digor an online checker to debug a routing problem.