DNS propagation is the delay before a DNS record change (new value, new nameserver, etc.) becomes visible globally. It's not an official protocol mechanism—it's colloquial for the effects of distributed caching across thousands of recursive resolvers.
How it works
When you publish a DNS record, it carries a TTL (Time To Live), measured in seconds. Recursive resolvers cache that record for up to its TTL. Once cached, a resolver keeps returning the old value until its cached copy expires—regardless of what your authoritative nameserver now says. "Propagation" is simply the time it takes for all those individual cached copies to expire and be refetched.
For example, if an A record has a TTL of 3600 seconds (1 hour), and you change the IP at 2:05 PM, resolvers that cached it at 2:00 PM will still serve the old IP until 3:00 PM. Only fresh queries after 2:05 PM get the new value immediately.
Nameserver (NS) changes take longer because the parent zone's NS record TTL and registry-level caching also apply.
Key timing tips
- Lower your TTL before a planned change, then wait for the old TTL to fully expire.
- Lowering TTL after a change doesn't help—already-cached records expire on their original schedule.
- Use DNS lookup to check when a change has reached your local resolver.
Propagation time varies by ISP, geography, and which resolvers have cached your record.
Tip"Propagation" is really just caching. Set a low TTL before a migration so old values expire quickly — there is no way to force every resolver to refresh early.