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DNS and connectivity, explained
DNS is the system that turns names you can read (example.com) into addresses computers can route to (203.0.113.10). It's invisible until it breaks — and when it does, the symptoms usually look like 'the internet is down' even though everything else works fine.
What DNS is
The Domain Name System is a globally distributed database mapping domain names to IP addresses (and other records). When you type a URL, your device asks a DNS resolver, which walks a chain — root → TLD (.com, .org) → authoritative nameserver — until it finds the answer, then caches it for next time.
Public vs ISP resolvers
By default you use your ISP's resolver. Public resolvers — Cloudflare (1.1.1.1), Google (8.8.8.8), Quad9 (9.9.9.9) — often resolve faster, leak less data, and offer features like malware blocking. Switching is a single-setting change on most routers and operating systems.
Common DNS failures
- NXDOMAIN — the name doesn't exist. Usually a typo or expired domain.
- SERVFAIL — the resolver couldn't get an answer. Often a misconfigured authoritative server.
- Stale cache — old IP cached after a server move. Flushing the local cache usually fixes it.
- Slow resolution — long first-byte times that look like a slow site but are actually slow DNS.
DNS security
Unencrypted DNS lets anyone on the path see which sites you visit. DNS over HTTPS (DoH) and DNS over TLS (DoT) encrypt the queries, hiding them from ISPs and network operators. Modern browsers and operating systems can enable DoH directly.
Troubleshooting DNS
Start by confirming the name actually resolves on a known-good resolver (e.g. 1.1.1.1). If it does, the issue is your local resolver or cache. If it doesn't, the authoritative DNS for that domain is broken. See the complete DNS troubleshooting workflow and common DNS errors.