DNS Propagation Checker

Propagation is really caching

DNS changes do not travel outward from your authoritative server. The moment you save a record, the authoritative server serves the new value to anyone who asks. What creates the delay is that most of the world does not ask: recursive resolvers at ISPs, offices and public services hold a cached copy and keep serving it until it expires. "Propagation" is just the staggered expiry of thousands of independent caches.

TTL controls the wait

Each record carries a time to live in seconds telling resolvers how long to cache it. A record with a 86,400 second TTL can be served from cache for a full day after you change it. The practical technique is to lower the TTL to 300 seconds at least one full old-TTL period before a planned migration, make the change, confirm it, then raise the TTL again. Lowering it at the same time as changing the record does not help, because resolvers are still holding the old record with the old long TTL.

Why you see the old value and someone else sees the new one

Two people using different resolvers are querying different caches with different expiry times. Even one person can get inconsistent answers, because large public resolvers run many nodes and your queries may land on different ones. This is normal and resolves itself as caches expire.

Negative caching bites hardest

If a name is queried before the record exists, the NXDOMAIN response is itself cached, for a duration set by the SOA record's minimum field rather than by the record's own TTL. That value is frequently much longer than people expect. Creating a record then immediately testing it, getting a failure, and having that failure cached is a common and frustrating sequence. Set up records before you point anything at them.

Checking properly

Query the authoritative nameserver directly to confirm what you published: dig @ns1.example.com example.com A. Then query public resolvers to see what the world currently gets. If the authoritative answer is right and public resolvers disagree, you are simply waiting on cache expiry. If the authoritative answer is wrong, the change did not save or you edited the wrong zone.