Comment by ButlerianJihad
12 hours ago
Actually that is not true. The IETF has expanded the definition of “TTL” and explicitly permits resolvers to serve “stale” RRs beyond their expiration time.
https://www.rfc-editor.org/info/rfc8767/
As a corollary, there is obviously no floor on refetching unexpired RRs, of course, except for efficiency concerns.
That's only when the authoritative server cant be reached though