DNS caching is not one clock
Why two clients can disagree after a DNS change, what a TTL actually controls, and how to investigate without chasing “propagation.”
A small technical notebook
Clear thinking.
Careful operations.
Field notes on how systems behave, where assumptions break, and how to make the next change a little easier to reason about.
The field notes
Two starting points
Networking / DNS
A checklist that closes the loop
Turn a sequence of commands into a bounded change: define the result, capture the starting point, and verify before calling it done.
About this notebook
Harbor Notes is a small collection of technical explanations and working methods. Each note favors a clear mental model, concrete checks, and honest limits over a universal recipe. Read it as a companion to your own system documentation—not a replacement for it.