"Propagation" is a slightly misleading word. DNS doesn't actually push changes outward; instead, every resolver caches old answers until their TTL expires, then asks again and gets the new answer.
So when you update a DNS record:
- Your authoritative nameservers reflect the change immediately.
- Resolvers that haven't cached the old answer get the new one on their first lookup — immediately.
- Resolvers WITH a cached old answer keep serving it until their cache expires.
The window during which different visitors see different answers is called "propagation." Typical durations:
- If TTL was 300 seconds (5 min): full global propagation within 5-10 minutes.
- If TTL was 3600 seconds (1 hour): 1-2 hours.
- If TTL was 86400 (24 hours): up to 24 hours, sometimes more.
The "24-48 hour" rule some hosts quote is conservative — it accounts for poorly-configured resolvers that ignore TTL entirely, plus DNS-prefetch caches in browsers and OSes.
How to check propagation: tools like whatsmydns.net query DNS resolvers in 20+ locations worldwide and show which ones have the new answer.
