TTL in DNS
The DNS TTL limits normal caching of an answer. A shorter new TTL does not retroactively shorten the validity of old answers already cached.
What does TTL mean in DNS?
TTL stands for Time to Live. In DNS, the value describes how long a resource record may normally be cached before its source should be consulted again. RFC9499 explains this cache lifetime and notes that a cache may also remove records earlier. The TTL is not an uptime guarantee for a service.
Example: preparing a portal move
A fictional team wants to change its portal's DNS address. Appropriately shortening the TTL in advance can limit the usual continued use of old answers. If the TTL is reduced only when the address changes, previously stored answers may remain cached according to their old value.
The team therefore plans the change, checks the data actually published and accounts for old answers still in use. A new address is not automatically used immediately by every client.
The TTL controls neither user login nor retention periods for portal files. The new server's reachability must also be checked independently.
Sources
Related terms
- Domain Name SystemDNS supplies data about names, such as a web server’s address. Name resolution, the server connection and application behaviour are separate steps.
- DNS zoneA DNS zone is an administrative unit for DNS data. Its boundaries follow delegation; not every subdomain automatically becomes a separate zone.
- A recordAn A record maps a DNS name to an IPv4 address. It does not configure the website or define HTTPS, paths or an HTTP redirect.
- Return-PathReturn-Path records the SMTP reverse path in a header. It explains the technical route for error reports, not a person’s identity.
- Envelope-FromEnvelope-From identifies the SMTP sender for transport and error feedback. It must be distinguished from the visible sender address.
- DMARC aggregate reportA DMARC aggregate report summarises a reporting mail system’s domain checks over a period. It helps examine sending sources and misconfigurations.
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