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For a planned DNS change, temporarily lower the TTL on the affected records ahead of cutover, wait for the old TTL to expire, make and verify the change, then restore the normal TTL once the new setup is stable. Lowering a TTL at cutover does not shorten cache entries resolvers already received under the previous, longer value.
What a DNS TTL controls
A DNS TTL is the period a resolver may reuse cached resource-record data before consulting its source again. It is a cache lifetime, not a command that pushes an update to every resolver at once. When a record changes, caches holding older answers can continue using them until their applicable cache periods expire; local caching and resolver behavior can affect when users observe the change.
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That means no single cutover time guarantees that every user will immediately receive the new answer. RFC 8767 defines the TTL as a duration for which a record may be cached, and also describes circumstances in which resolvers may serve stale data after expiry to improve resilience: RFC 8767.
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How to lower TTLs before a planned DNS change
- Identify the records involved. Inventory the relevant A and AAAA records, CNAMEs, MX records, and, for delegation work, NS records and associated delegation data. Note their current TTLs and consider whether negative caching could affect a name or record type that will be created.
- Lower the TTLs in advance. Set an appropriate temporary value on the records that will change. Allow the old TTL interval to pass before cutover: that earlier value determines how long answers already cached under it may remain in use. Changing the TTL does not retroactively change those answers.
- Check the authoritative answers and readiness. Confirm that authoritative servers return the intended lower TTLs and that the new destination is ready before directing traffic to it.
- Make the DNS change and verify it. Check the authoritative answer and the service itself. Where practical, keep the old destination available during the transition because different resolvers may hold answers fetched at different times.
- Restore the normal TTL after the new setup is stable. Verify the authoritative response again after restoring it.
There is no universal advance interval or temporary TTL that fits every zone. Set the change window using the previous TTL, the records and providers involved, and the consequences of delayed adoption. RFC 9199 describes lowering TTLs before a major operational change and raising them afterward: RFC 9199.
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Why not use very short TTLs all the time?
Short TTLs can make resolvers eligible to refresh answers sooner, but they can also increase query frequency to authoritative servers. They do not guarantee equally rapid adoption everywhere: RFC 9199 notes that many recursive resolvers use minimum caching periods of tens of seconds, limiting the added agility from values below those floors. RFC 8767 also documents stale-answer service in specified resolver failure circumstances after TTL expiry.
Longer TTLs reduce repeat lookups and support cache reuse, but can make a later change slower to reach caches. Cloudflare likewise describes this trade-off and notes that local cache behavior can extend the time before a change is observed: Cloudflare’s TTL overview.
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Account for negative caching and delegation changes
Negative answers
Resolvers may cache negative responses such as NXDOMAIN (the name does not exist) or NODATA (the name exists, but the requested record type does not). If a name or record type was queried before it existed, setting a short TTL on the new positive record does not remove the cached negative answer. RFC 9520 describes negative caching when an SOA record supplies a TTL, while RFC 9077 specifies that the effective negative TTL is the minimum of the SOA record TTL and SOA.MINIMUM. If a negative response is plausible during the change, include that negative TTL in the plan: RFC 9520 and RFC 9077.
Delegation and glue
A delegation change is not the same as changing an application’s address record. It can involve the parent and child zones, NS records, and glue addresses. RFC 9199 notes that for in-bailiwick authoritative servers, the A/AAAA TTLs should be no greater than the corresponding NS TTL. Identify and verify the relevant delegation path rather than assuming that changing one application record covers it.
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What the standards’ TTL figures mean
| Figure | Context | How to use it |
|---|---|---|
| 604,800 seconds (7 days) | RFC 8767 (2020) recommends this as a cap for TTL values in its updated definition, reflecting modern resolver practice. | It is not a universal target TTL for operators. |
| 2 days (48 hours) | RFC 9199 (2022) gives this as the TTL for NS records for TLDs in the root zone. | This is an example for that delegation context, not a general application-record setting. |
| 1 hour | RFC 9199 (2022) cites .cl NS records as an example of lower values in authoritative records. | This example does not establish a recommended temporary TTL for every change. |
| Tens of seconds | RFC 9199 (2022) observes that many recursive resolvers use minimum caching periods in this range. | This is an operational observation, not a rule followed by every resolver. |
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