Suggest an editImprove this articleRefine the answer for “What is TTL in DNS?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**TTL (Time To Live)** in DNS is the **lifetime of a DNS record in cache**, measured **in seconds**. **Key point:** TTL is a trade-off between speed and flexibility - a high TTL reduces the number of DNS queries, while a low TTL speeds up how quickly changes take effect.Shown above the full answer for quick recall.Answer (EN)Image**TTL (Time To Live)** in DNS is the **lifetime of a DNS record in cache**, measured **in seconds**. In simpler terms: **TTL shows how long a DNS answer can be stored and used without asking the DNS server again**. --- ## Why TTL is needed DNS queries can be made by: - the browser - the operating system - the provider's DNS servers To avoid asking the DNS server **every time**, caching is used. TTL says: > "This answer can be considered valid for N seconds." --- ## How TTL works (a simple example) Suppose a record has: ``` example.com A 93.184.216.34 TTL = 300 ``` This means: - the DNS answer is cached **for 300 seconds (5 minutes)** - during this time the IP is taken from cache - new queries do not go to the authoritative DNS After the TTL expires: - the record is removed from cache - on the next request, DNS is queried again --- ## Where TTL applies TTL is taken into account: - in the browser - in the OS - in recursive DNS servers - in proxies and CDNs TTL **is not the same as the lifetime of the record on the server**, only the caching time. --- ## Why TTL matters ### High TTL - fewer DNS queries - faster performance - slow propagation of changes ### Low TTL - changes take effect quickly - more DNS queries - higher load TTL is a **trade-off between speed and flexibility**. --- ## A common real-world scenario Before migrating a site: - TTL is lowered (for example, to 60 seconds) - the IP is changed - after the migration, TTL is raised back This allows: - minimizing downtime - switching users over faster --- ## Real-life example TTL is like the validity period of a certificate: - while the period has not expired, it is accepted - once it expires, a new one is needed --- ## Short interview answer Remember this formulation: > **TTL in DNS is the time, in seconds, during which a DNS record can be stored in cache and used without querying the DNS server again.**For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.