Time to live
(also TTL)
Time to live definition
Time to live is a setting determining the length of time DNS resolvers should cache a particular DNS record. A DNS record’s time to live is measured in seconds — for example, a value of 3,600 means that the DNS resolver should cache the record for an hour before requesting a new one.
See also: DNS cache, DNS filtering, DNS flushing, DNS hijacking, DNS over HTTPS, DNS port, DNS query, DNS record, DNS redirection, DNS resolution, DNS sinkhole
Why DNS resolvers use time to live
Temporarily storing DNS records in the cache memory of a DNS resolver can speed up DNS lookups — if the DNS resolver already has the IP address of a particular domain in its cache, it can respond to a query immediately, without the need to send another request to the authoritative DNS server.
However, if the IP address of a particular domain has changed since the DNS record was cached, the user will not be able to connect. Time to live values solve the problem by requiring DNS servers to periodically update their cache with the most recent results. Time to live values must balance this need for updates with DNS resolution efficiency.