Resources
What is a TTL?
The TTL is how long a resolver may keep an answer before asking again. It decides how fast a change becomes visible.
A high TTL saves queries and rides out short outages. A low TTL makes changes propagate quickly and costs more traffic.
Before a planned move, lower the TTL of the affected records to a few minutes — at least one old TTL period ahead of the change, so caches have already picked up the shorter value. Raise it again once the move is done.
The TTL is counted by every cache separately. There is no way to force expiry from your side; that is why the preparation matters.
Negative answers are cached too, governed by the minimum field of the SOA.