How DNS resolution works

What you take away

• A cold lookup asks four parties: your recursive resolver, then root, then the TLD servers, then the domain's authoritative servers.
• The resolver does the walking and caches every answer, so almost every real lookup is a cache hit costing nothing.
• Caching happens in layers you do not control — browser, OS, resolver — which is why DNS changes are never immediate.
• A CNAME is an alias that costs another resolution; an A record is the address itself.

How the class is laid out

1. The problem
2. The simple version
3. One cold lookup
4. Check your understanding