TTL
Value that tells resolvers how long a DNS record may be cached before re-querying.
TTL (Time To Live) is a value in seconds attached to every DNS record. It tells a resolver or client how long the answer may be kept in cache before it must be fetched again from the authoritative source. The value is set by the domain owner in the zone and returned alongside the record itself.
Low TTLs (for example 60 or 300 seconds) make changes to an A-record or CNAME-record propagate quickly, but increase the number of queries hitting authoritative servers. High TTLs (hours or days) reduce DNS traffic and improve performance, but make any change slower to take effect globally.
A common operational pattern is to lower TTL to a few minutes ahead of a planned migration, then raise it again once the change has stabilised. Resolvers are not always disciplined about expiry, so real-world propagation can take somewhat longer than the TTL would suggest.
Puntos clave
- Specifies how long a record may be cached, in seconds
- Set per record in the zone file by the domain owner
- Low TTL means fast propagation, higher query load
- High TTL reduces DNS traffic but slows changes
- Typically lowered ahead of planned migrations
- Resolvers may, in practice, cache longer than the TTL allows