A domain change has to travel through caches
A domain name is the memorable part of a web address; behind it, the Domain Name System (DNS) helps computers find the server’s numerical internet address. When a site changes servers, its DNS record is updated to point to the new address. But that update is not instantly fetched by every network and device.
To avoid looking up the same domain repeatedly, internet providers and other systems temporarily save DNS answers. This saved copy is called a cache. It makes routine browsing faster and reduces repeated work, but it also means a network may keep using the old address after the site owner has changed the record.
The expiration timer sets the pace
Each DNS answer has a time-to-live, or TTL: a timer that tells caches how long they may reuse it before checking again. Once the timer runs out, a cache can request the current record and learn the new address. Until then, visitors using that cache may still be directed to the old server, while others already reach the new one.
That is why a domain change can appear uneven. Two people visiting the same site at the same moment may get different results, not because the change happened twice, but because their networks are holding DNS answers with different expiration times.
The old server can still matter
During the transition, keeping the old server available can help prevent visitors with stale cached records from hitting a dead end. The change is less like flipping a single switch and more like waiting for many separate timers to expire. Once caches refresh, they converge on the new address—and the old one can finally stop receiving those lingering requests.
