Time to Live (TTL)
A numerical counter or duration field indicating how long a data unit (such as a DNS record or an IP packet) remains valid before being discarded or re-queried.
Entity Relationships (GEO Conceptual Hierarchy)
Taxonomy ModelTechnical Explanation & Operational Mechanics
In DNS, TTL is measured in seconds and specifies how long intermediate caching resolvers and client operating systems may store and serve a DNS record without querying the authoritative nameserver again. A short TTL (e.g. 60–300 seconds) allows rapid cutovers during server migrations or failovers, at the cost of higher query volumes. A long TTL (e.g. 86400 seconds / 24 hours) reduces network overhead and lookup latency but delays propagation when IP addresses change. In IP networking, TTL is an 8-bit hop counter decremented by each router to prevent packets from looping endlessly in routing loops.
Technical Example & Practical Implementation
Authoritative zone TTL versus recursive resolver cache countdown
; BIND Zone File Entry:
; Name TTL Class Type Target
api.example.com. 300 IN A 198.51.100.42
; Caching Resolver Timeline:
; Time = 0s: Resolver queries authoritative server, receives IP and TTL 300.
; Time = 100s: User 2 asks resolver -> served instantly from cache (TTL remaining: 200s).
; Time = 300s: Cache TTL hits 0s. Record is purged (expired).
; Time = 301s: User 3 asks resolver -> resolver must query authoritative server again.Related Topic Ecosystem & Next Steps
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