DNS Propagation

DNS propagation is the window during which a change made on an authoritative DNS server becomes visible to clients around the world. Despite the name, nothing is actively pushed. The new record is published instantly on the authoritative servers, but recursive resolvers and operating-system stubs keep serving the previous answer until their cached copy expires.

The expiry is controlled by the TTL on the original record, not on the new one. If www.example.com had a TTL of 86400, resolvers may legally serve the old A value for up to 24 hours after the change, no matter how quickly the authoritative servers updated. Lowering the TTL to, for example, 300 a day or two before a planned change is the standard way to shorten the propagation window.

Negative answers are cached too. The minimum field in the zone's SOA record (sometimes via the negative TTL) controls how long an NXDOMAIN or empty answer is remembered. A name that did not previously exist can therefore continue to resolve as missing for some time after the A-record is added, which surprises users who expect new names to work immediately.

Delegation changes — moving a domain to new NS records at the registry — follow the same model but at the parent zone. Different resolvers see the change at different times depending on when they last fetched the parent delegation. During the transition both old and new authoritative servers should answer with identical data so users land on the right host whichever set their resolver still trusts.