DNS Propagation
Why DNS Changes Are Not Visible Everywhere at Once
DNS propagation is the period between changing a DNS record and the moment every user sees the new answer. The term is common, but it is slightly misleading. Nothing is pushed out across the internet. Each resolver keeps the old answer until its cached copy expires, then asks again and receives the new one.
The change therefore becomes visible at different times in different places. One visitor may reach the new server within minutes, while another still gets the old address because their resolver cached it an hour earlier. The delay is a side effect of caching, which is designed to make DNS fast.
What Slows Down a DNS Change
Several layers can keep old answers in place:
- Resolver caches: each resolver holds a record for its TTL. Until then, the old value is served, as described in how TTL works.
- Device caches: browsers and operating systems may keep an answer a little longer on top of the resolver’s own DNS caching.
- Resolvers that ignore TTL: some hold answers longer than the TTL says, which makes timing even less predictable.
- Negative answers: if a name was missing before you created it, the “not found” answer may linger.
- Nameserver changes: changing the nameservers of a domain means the registry must publish the new delegation, and that update is cached too. This step often takes the longest.
Changes to records inside your zone generally settle within the old TTL. Changes to nameservers depend on the registry and are harder to predict. For background on how nameservers work, see what nameservers do.
Example: Moving a Site to a New Host
Suppose a site moves to a new host and its A record changes from the old IP address to the new one. The record had a TTL of four hours. Some visitors reach the new server straight away, while others keep reaching the old one for up to four hours. If the old server is shut down at once, those visitors see errors until their cached answers expire.
A safer order is to lower the TTL well before the move, make the change, keep the old server running until the old answers have expired, and then shut it down. This is common migration practice, not a guarantee, because some resolvers ignore TTL values.
Frequently asked questions
How long does DNS propagation take?
It depends on the TTL and the caches involved. Changes to records within a zone usually settle within the old record’s TTL, so minutes to a few hours is common. Nameserver changes can take longer because they go through the registry. No exact time is guaranteed, and some resolvers do not follow TTL values.
Can I speed up DNS propagation?
You cannot force resolvers to forget old answers, but you can prepare for a change. Lower the TTL before the planned switch so cached copies expire sooner. Keep the old service running until the change has settled, and expect some visitors to see the new answer later than others. Clearing your own device cache only affects your computer.