TTL (Time to Live) is a value in seconds attached to every DNS record that tells resolvers how long they may cache the answer. When the timer runs out, the resolver discards the record and queries the authoritative nameserver again.
Why it matters
TTL controls how fast a DNS change reaches users. If an A record has a TTL of 86400 (24 hours), a resolver that cached it a minute ago can keep serving the old IP for almost a full day after you edit it. A low TTL speeds up failover and migrations but increases query volume to your nameservers.
The same name is also used for the IP header field, where it is a hop limit that stops packets from looping. That is unrelated to DNS caching.
Example
$ dig +noall +answer example.com A
example.com. 287 IN A 203.0.113.10The record was published with a TTL of 300. The resolver answered from cache, so the remaining TTL is 287 and counts down on each query. When it hits 0, the next query fetches a fresh copy.
Common mistakes
- Lowering the TTL at the moment you change the record. Resolvers already holding the old answer keep it for the old TTL, so lower it at least one full old-TTL period beforehand.
- Leaving a 60-second TTL on records that never change, which adds load and latency for no benefit.
- Forgetting negative caching: a "no such record" answer is cached for the SOA minimum value, so a freshly created record can still look missing for a while.
- Assuming every resolver obeys your TTL. Some enforce their own minimum or maximum.
Related
Get notified when this term updates
Plus occasional practical tips on uptime and monitoring, nothing else. Unsubscribe anytime.
यह पेज सामान्य जानकारी है, जिसे हमारी संपादकीय टीम ने लिखा है और दस्तावेज़ीकरण बदलने पर अपडेट किया जाता है। सर्वर और प्रदाता अलग-अलग होते हैं, इसलिए बदलाव पहले सुरक्षित तरीके से जाँचें। देखें: संपादकीय नीति और अस्वीकरण.