DNS Outages: A Beginner's Guide to the Internet's Address Book

You type github.com and expect a page to load. Between the keystroke and the pixels, DNS has to convert that name into an IP address — the actual location of the server. When DNS fails, the servers are still running fine, but nobody can find them.

How DNS actually resolves a name

Your OS asks the DNS resolver configured on your machine (usually your ISP's, or 1.1.1.1 / 8.8.8.8 if you changed it).
If the resolver has the answer cached, it returns it instantly.
If not, it asks a root nameserver, then a TLD nameserver (.com), then the domain's authoritative nameserver.
The answer comes back with a TTL — how long everyone should cache it.

The five failure modes

1. Bad record push

Someone updates a DNS record incorrectly (wrong IP, missing entry). Every resolver globally starts serving the wrong answer until the TTL expires. Facebook's 2021 outage was this on a huge scale.

2. Expired domain

The domain registration lapses. Every record disappears until it's renewed and the TLD propagates the update.

3. DNSSEC misconfiguration

DNSSEC signs records to prevent spoofing. A misconfigured signature causes every validating resolver to reject the domain.

4. Nameserver outage

The authoritative nameservers themselves go offline. If a domain uses only one provider and that provider has an incident, resolution fails.

5. Resolver outage

Your specific DNS resolver has problems. Switching to 1.1.1.1 or 8.8.8.8 fixes this instantly.

How to diagnose a DNS problem

Try loading the site on cellular data — that uses a different resolver.
Run dig example.com (or nslookup example.com on Windows) to see the raw response.
Try DNSChecker to see how the record resolves worldwide.
Search the service on Down For All Or Just Me — if our probes are getting DNS errors, so is everyone else.

What you can do proactively

If you run a site, use two DNS providers, keep TTLs short enough to fix mistakes fast (5–15 minutes), and monitor your records externally.