DNS propagation / TTL
TTL (Time To Live) is a value attached to every DNS record that tells resolvers how many seconds they're allowed to cache an answer before checking again. "DNS propagation" describes the real-world delay after a DNS change before every resolver worldwide that cached the old answer has that cache expire and fetch the new one -- it isn't instant, and the wait is bounded mainly by whatever TTL was set on the old record, not by the change itself. A short TTL (like 300 seconds) set in advance of a planned change, such as a server migration, lets the old answer expire quickly once the real change happens; a long-standing TTL of 86400 seconds or more means stragglers can take a full day or more to catch up.
By AdminKit team, Netbase JSC · Updated