TTLWerte

TTLWerte is the German term for time-to-live values used across information technology to control how long data items may be kept before becoming stale. The exact meaning depends on the context, but the underlying idea is consistent: a countdown or deadline after which the item is considered invalid or in need of refresh.

In the Domain Name System, TTL is a field in resource records that specifies how long resolvers and intermediate caches may store the record. TTL values are expressed in seconds and set by the zone administrator; a longer TTL reduces query load and can improve response times during normal operation, while a shorter TTL allows quicker reflection of changes but increases DNS traffic. A TTL of 0 means the record should not be cached by resolvers, though some may cache briefly.

In IPv4, TTL is an eight-bit field in the IP header that decrements by one at each hop; when it reaches zero, the packet is discarded and an ICMP Time Exceeded message may be returned. The TTL mechanism prevents routing loops and provides a basic hop limit for routing. Traceroute uses varying TTL values to elicit responses from intermediate devices.

TTL values are also used in caching systems (such as memcached or Redis) and in messaging or queue systems to expire items after a period, ensuring stale data is discarded. In these contexts, TTLs are typically measured in seconds or milliseconds and configured per item or per queue.

Choosing TTL values involves a trade-off between data freshness and performance. Longer TTLs reduce external lookups but risk serving outdated data after updates; shorter TTLs increase accuracy at the cost of higher load. TTL semantics are defined in standards such as DNS (RFC 1035) and IP (RFC 791).