DNS changes
An updated authoritative DNS server normally answers with the new record immediately. Other networks may continue using a cached older answer until its remaining TTL expires.
Authoritative sourceThe DNS host stores the current record.
Resolvers cache answersTTL controls how long they may retain them.
Results vary temporarilyDifferent visitors can see different answers.
What happens
Recursive DNS resolvers ask authoritative nameservers for a record and may cache the reply. After you edit the authoritative zone, resolvers holding the previous reply can keep using it until that cached TTL reaches zero.
How long
A record with a five-minute TTL usually clears quickly; one cached for several hours can take correspondingly longer. Lowering a TTL immediately before a change does not shorten copies that were already cached under the previous value.
Troubleshooting
Confirm the new value directly against each authoritative nameserver, then compare public resolvers. If authoritative servers disagree, fix or synchronise the zone. If they agree, allow caches to expire and avoid repeatedly changing the record.
Changing delegation or glue involves registry data and can have additional caching beyond an ordinary A, MX or TXT record edit.
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