DNS propagation

What DNS propagation really is

Nothing actually spreads across the internet when you change a DNS record. Your nameservers start serving the new value at once. What lags behind are the resolvers (your ISP's, Google's, Cloudflare's) that cached the old value before the change: each keeps it until its time to live (TTL) runs out, then asks again.

A resolver counts that TTL down and reports what is left with every answer. So instead of a map of ticks and crosses, this checker tells you which resolvers still hold the old record and when each copy expires.

How the check works

• Source of truth: it asks your zone's own nameservers directly, so it knows what is published right now, and compares their zone serials to catch a nameserver that missed an update.
• Delegation: it asks the parent zone (the registry for a registered domain) which nameservers it lists, and how long that list is cached. After a nameserver change, that registry TTL (often 2 days for .com) is what you are waiting for.
• Resolvers: it asks 22 resolvers run by different operators on five continents: public services such as Google, Cloudflare, Quad9, OpenDNS, AliDNS, Yandex and India's national resolver, and ISP or research-network resolvers in Taiwan, South Korea, Australia, Nigeria and Tunisia, which answer from inside their own region. South America isn't covered yet.
• Countdown: every resolver with an old answer gets the exact time its cached copy expires. Leave the page open and it re-checks every minute until all of them match.

Reading the result

• Current: the resolver gives the same answer as your nameservers, or the value you entered in "Expected value".
• Old: the resolver still has an earlier answer cached. It will ask again when the countdown reaches zero.
• Not found yet: the resolver looked the name up before the record existed and cached "doesn't exist". That lasts for the negative-caching time in the zone's SOA record.
• Rotates: your nameservers hand out different answers in turn (load balancing or location-based DNS). Any answer from that set counts as current.
• Nameservers disagree: your nameservers are on different versions of the zone, so resolvers get mixed answers until they catch up.

Many large resolvers are anycast: the same address is served from dozens of sites, and we reach the one nearest our server. That is why the map pins each operator in its home country rather than claiming a city.

Questions

How long does DNS propagation take?

At most the TTL the old record had when resolvers cached it. Records commonly use 5 minutes to 1 hour; a nameserver change follows the registry's TTL, often 48 hours for .com. The countdown here shows the real remaining time for each resolver.

How do I make a DNS change propagate faster?

Lower the record's TTL to 300 seconds at least one old TTL before the change, make the change, then raise the TTL again once every resolver shows the new value. You can't shorten a copy that is already cached.

All resolvers show the new value but my computer still gets the old one. Why?

Your ISP's resolver, your operating system and your browser each keep their own cache. Flush the OS cache (for example ipconfig /flushdns on Windows) and restart the browser, or wait for the TTL to run out.

What does "Expected value" do?

Without it, resolvers are compared with what your nameservers serve right now. Enter the IP, hostname or TXT value you are waiting for, and the check also tells you if your nameservers don't serve it yet, which no amount of waiting will fix.

Why do some resolvers give a different IP even when nothing changed?

Large sites use load balancing or location-based DNS, so nameservers hand out different addresses to different resolvers. The checker asks each nameserver twice to spot this and counts any answer from the set as current.