Уроки модуля (1/4)
Cache e scadenza
Caching and expiration
Resolvers cache answers for the TTL they receive. That makes repeated lookups faster and reduces traffic, but it means an authoritative change is not visible everywhere immediately.
A simple timeline
At 10:00, a resolver caches api.example.test → 192.0.2.10 with a TTL of 600 seconds. At 10:04, the authoritative value changes to 192.0.2.20. A resolver holding the earlier answer may continue to return it until about 10:10. Changing the authority does not instantly refresh every cache.
For a planned migration, lower the TTL early enough for the old TTL to expire, make the change, check from several resolvers, and then restore a suitable TTL. Very low TTLs increase query load and do not guarantee that every application follows updates at the same moment.
Laboratorio guidato: Cache e cambio di indirizzo
Il laboratorio simula la cache positiva; non usa orologi né resolver reali.
Simulazione didattica locale: nessuna query DNS viene inviata.
When comparing observations, record the name and type, server, timestamp, remaining TTL, response code, and whether the answer came from an authority or a cache.
Check your understanding
Choose the best answer. This quiz runs locally and sends no DNS queries to real domains.
Does lowering a TTL now immediately remove an answer cached yesterday?