Naming: DNS and the Resolution Path
DNS maps human-readable names to records such as addresses. A recursive resolver can answer from cache or follow delegations from the root through a top-level domain to an authoritative server. TTL values limit how long cached records may be reused.
What a learner can do afterwards
- Walk a name resolution from the root through to the answer
- Explain what the time to live decides and who honours it
- Say what a stale cached answer looks like from a user's side
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DNS maps human-readable names to records such as IP addresses. A browser usually asks a recursive resolver. If the resolver has usable cached data, it can answer from cache. A cache hit skips the referral walk, so the answer comes back faster. Otherwise, the resolver follows referrals to find an authoritative answer.
For shop.example.com, an uncached iterative lookup can ask a root server for the .com name servers, ask a .com server for the authoritative servers for example.com, and ask one of those servers for the record. A recursive resolver performs this work for the browser.
A DNS record includes a time to live, or TTL. It tells a caching resolver how long the record may be retained for reuse. When the TTL expires, a later lookup needs a fresh answer. The resolver does not have to ask at the exact expiry moment.
After an address changes, some caches may still hold the old record while its TTL has time left. A user can then reach the old server until that cached answer expires and a fresh lookup supplies the new one.
A resolver uses cache when it can, follows DNS delegations when it must, and uses TTL to limit cached answers.
Original instructional content authored for os-taxonomy.
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