A small reference notebook
Keep names and addresses separate
Two useful labels
A name is a label that people can keep while an address changes. A DNS lookup connects those two ideas. Keeping them separate makes a connection problem easier to describe: first record the name you requested, then the address your resolver returned. Neither fact, by itself, tells you whether the service at that address is healthy.
A cache is a local observation
Answers can remain in a cache for a limited time. Two devices may therefore observe different answers without either being dishonest. Note when an observation was made and which resolver supplied it. After changing one thing, repeat the same small check instead of changing several unrelated settings.
Write down the boundary
An address lookup, a connection and an application response are different observations. A useful note says exactly which one succeeded. That small habit prevents a successful first step from being mistaken for a completed request.