Where does DNS caching happen?
At several layers: the browser, the operating system, a local resolver or router, and the ISP's recursive resolver. Only if every layer misses does a recursive lookup go out through root, top-level domain and authoritative servers. Each answer carries a time-to-live that says how long it may be cached.
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From Enter Key to Pixels: What Happens When You Type a URLDNS caches, TCP, TLS, HTTP, then HTML parsing, the render tree, layout and paint. Every stage is a place a page can be slow, and a place to fix it.
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