The naming problem
Names are for people; addresses are for delivery.
A browser can start with a name, but it cannot send an IP packet to a word. It asks a DNS resolver for an answer, then uses the returned address for the next network step.
DNS is distributed. A resolver can answer from its cache, ask another resolver, or follow the hierarchy to an authoritative server that manages the domain.
Build the model
The resolution chain
Cache
A recent answer may already be available locally or at the configured resolver.
Recursive resolver
The resolver does the lookup work on behalf of the device.
Authoritative server
The server responsible for a domain can provide its current records.
DNS record
An A or AAAA record maps a name to an IPv4 or IPv6 address.
Mini experiment
Resolve a name
Step through the simplified lookup. Notice where the answer can be found and when another server must be asked.
The resolver checks whether it already knows a still-valid answer for the name.
A cache hit is quick, but cached answers expire according to their TTL (Time to Live).
Knowledge check
Test your DNS model
Answer five questions. The answer order changes each time.