How the check works
Your browser sends the name and record type to our server, which asks every resolver below at the same time over DNS over HTTPS and waits up to 3.5 seconds for each. You see each answer as it came back: the records, the TTL each resolver has left on its cached copy, and how long the answer took.
When you change a record, a resolver that asked before keeps the old answer until its TTL runs out, then asks your name servers again. Resolvers asked at different times run out at different times, which is why a change shows up at some resolvers before others. The TTL left tells you when each one will ask again at the latest.
The resolvers we ask
Each runs many sites under one address (anycast), and each site can hold its own cache. Our server only reaches the site nearest to it, so another site of the same resolver may still answer differently for a while. Your internet provider's resolver is not in this list; it follows the same TTL rules.
| Resolver | Run by | Based in |
|---|---|---|
| Cloudflare 1.1.1.1 | Cloudflare | United States |
| Google Public DNS | United States | |
| Quad9 | Quad9 Foundation | Switzerland |
| OpenDNS | Cisco | United States |
| AdGuard DNS | AdGuard | Cyprus |
| NextDNS | NextDNS | United States |
| Control D | Control D | Canada |
| Mullvad DNS | Mullvad VPN | Sweden |
| Hurricane Electric | Hurricane Electric | United States |
| DNSPod | Tencent | China |
| 360 Secure DNS | Qihoo 360 | China |
Example
You move example.com to a new VPS at 203.0.113.10. You change its A record, enter example.com here, choose A and type 203.0.113.10 as the expected value. Eight resolvers show the new address; three still show the old one with up to 40 minutes of TTL left. Within 40 minutes those three ask again and get the new address too.
Questions
How long does DNS propagation take?
At most as long as the old record's TTL. Resolvers keep an answer for its TTL and then ask again, so a record with a TTL of 3600 seconds reaches every resolver within an hour. Changing the name servers themselves can take up to two days, because the delegation at the registry has a longer TTL.
Why do resolvers show different answers?
Each resolver keeps its own cache. One that asked just before your change still has the old answer until its TTL runs out; one that asked after has the new one. Large sites also answer differently by location on purpose, so their A and AAAA records can differ between resolvers even when nothing changed.
Does this check DNS from around the world?
It checks the big public resolvers, each from the site nearest our server. These resolvers run sites on every continent under one address, and each site can have its own cache, so the result shows what each resolver answers from there. Your internet provider's own resolver is not among them.
How can I make a DNS change spread faster?
Lower the record's TTL, for example to 300 seconds, at least one old TTL before the change, so caches hold the old answer only for minutes. After the change you cannot empty other resolvers' caches, but Cloudflare and Google each have a public page to purge one name from theirs.
Every resolver shows the new value, but my computer does not. Why?
Your computer, browser or router may still hold the old answer, or your internet provider's resolver has not asked again yet. Flush the local DNS cache or restart the browser, check for an entry in the hosts file, and wait for the old TTL to run out.