Time to live

In computing applications, TTL is commonly used to improve the performance and manage the caching of data.

[2][3] The time-to-live value can be thought of as an upper bound on the time that an IP datagram can exist in an Internet system.

The TTL field is set by the sender of the datagram, and reduced by every router on the route to its destination.

In theory, under IPv4, time to live is measured in seconds, although every host that passes the datagram must reduce the TTL by at least one unit.

TTLs also occur in the Domain Name System (DNS), where they are set by an authoritative name server for a particular resource record.

[4][jargon] Shorter TTLs can cause heavier loads on an authoritative name server, but can be useful when changing the address of critical services like web servers or MX records, and therefore are often lowered by the DNS administrator prior to a service being moved, in order to reduce possible disruptions.

Newer DNS methods that are part of a disaster recovery (DR) system may have some records deliberately set extremely low on TTL.