Glossary · ENCheck a domain

TTL

TTL means “time to live.” For a DNS record, it is the number of seconds that a resolver may keep a temporarily saved answer before it should ask again for fresh information. A resolver is software that looks up DNS answers for a device or application. The TTL helps balance faster repeat lookups against how quickly changes can be noticed.

How does a DNS TTL affect a change?

Suppose an A record has a TTL of 3,600 seconds, or one hour. A resolver that retrieves that record can keep the answer in its cache for up to that period. If the owner changes the record five minutes later, a resolver that already has the old answer may continue using it until its cached copy expires. Other resolvers that have not cached the record may see the new answer sooner.

The TTL does not mean every visitor will wait exactly that long, and it is not a timer that pushes an update across the Internet. It sets a limit on how long a DNS answer may be reused from that cache. A record's TTL can differ from another record's TTL, and resolver behavior can also affect when users observe a change.

Is TTL the same as DNS propagation?

No. “DNS propagation” is a common informal phrase for the period in which people may see different answers after a DNS change. DNS does not send the change to every resolver at once. Cached answers expire according to their TTLs, after which resolvers can retrieve current data. A DNS cache stores these answers; the TTL helps determine how long a cached record remains usable.

For a planned server move, an owner may lower the relevant TTL ahead of time so caches refresh sooner after the address change. The lower TTL must be in place long enough for older cached values to expire before the move. This is a planning choice, not a guarantee that all clients will update at one exact moment.

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