TTL (time to live)

The number of seconds a resolver may keep an answer before asking again. In example.com. 3600 IN A 203.0.113.10, 3600 is what is left of it: a resolver holding that answer serves it for up to an hour without contacting anyone. The trap is the direction it works in. The TTL you set now governs the next change, not this one: caches are still counting down the value published before you edited the record, so lowering it to 300 on migration day changes nothing for the visitors already holding 86400. Lower it two days ahead, while the old one still has time to expire everywhere. Raise it back to 3600 or more once the address is stable: a short TTL multiplies queries and slows the first visit.