DNS propagation is the informal name for the delay between changing a DNS record and every resolver worldwide returning the new value. Despite the name, nothing is pushed out: the authoritative nameservers update immediately, and the delay comes from resolvers holding cached copies until the TTL expires.
Why it matters
During propagation, some visitors see the new server while others still reach the old one. That inconsistency matters during migrations, email provider switches and certificate validation. Changing nameservers can take longer than editing a record, because the parent zone's NS records are cached too, often for up to a day or two.
Example
Query the authoritative server and two public resolvers and compare:
dig @ns1.dnshost.example example.com A +short
dig @1.1.1.1 example.com A +short
dig @8.8.8.8 example.com A +shortIf the first shows the new IP and the others the old one, the change is correct and you are waiting on caches. The remaining TTL in a normal dig answer shows how long.
Common mistakes
- Waiting "48 hours" by habit instead of reading the old TTL, which is the real upper bound for a record change.
- Checking only your own machine, which may have its own browser and operating system DNS caches.
- Changing the record again because it "didn't work", which restarts the confusion.
- Lowering the TTL right before a cutover instead of in advance.
Related
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