---
title: "TTL"
description: "TTL defines how long data such as a DNS record or cached response stays valid before it must be refreshed. See how it controls propagation and caching."
url: "https://nodea.io/en/glossary/ttl"
lang: "en"
updated: "2026-07-13"
---

# TTL

> TTL (Time to Live) specifies how long a piece of data, such as a DNS record or a cached response, remains valid before it must be fetched again.

**TTL** (Time to Live) specifies how long a piece of data remains valid before it must be discarded and fetched fresh. It appears in several contexts, most notably in [DNS](https://nodea.io/en/glossary/dns), where it controls how long resolvers may cache a record, and in web caching, where it defines how long a stored response can be reused. In every case, TTL is a countdown that governs the trade-off between freshness and efficiency.

## TTL in DNS

Each DNS record carries a TTL telling resolvers how many seconds they may cache the answer. During that window, a [DNS server](https://nodea.io/en/glossary/dns-server) or client reuses the cached value instead of asking again, which speeds up lookups and reduces load. The cost is propagation delay: if you change a record such as a [CNAME](https://nodea.io/en/glossary/cname-record), resolvers keep serving the old value until the TTL expires. That is why teams lower the TTL before a planned migration, so changes take effect quickly, then raise it afterwards to benefit from longer caching.

## TTL in caching and beyond

The same principle governs web [caching](https://nodea.io/en/glossary/cache-and-microcaching): a cached page or asset is served directly until its TTL runs out, after which the cache fetches a fresh copy. A long TTL maximises performance but risks showing stale content; a short TTL keeps data current at the cost of more frequent refreshes. TTL also appears at the network level, where it limits how many hops a packet may travel before being discarded, preventing packets from looping forever. Across all these uses, choosing the right TTL is a balancing act: it decides how quickly changes propagate versus how much you benefit from reusing stored data. Understanding TTL is essential whenever you plan a change whose effects depend on caches clearing out.

### Why lower the TTL before changing DNS records?

A lower TTL means resolvers cache the old value for a shorter time, so a change propagates faster. Teams often reduce the TTL a day before a migration, make the change, then raise it again once everything is stable.

## Related

- [DNS](https://nodea.io/en/glossary/dns)
- [DNS Server](https://nodea.io/en/glossary/dns-server)
- [Cache and microcaching](https://nodea.io/en/glossary/cache-and-microcaching)
- [CNAME record](https://nodea.io/en/glossary/cname-record)

---

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