TTL is an abbreviation for Time-To-Live, which is one of the most utilized parameters in networking, DNS, HTTP caching, and other systems where both efficiency and timing matter.
What is TTL?
It refers to a time value that is placed on data packets which defines for how long the data will be valid. Once it expires, the data is either deleted or updated from the source.
Various systems can have different values depending on what they intend to achieve. TTL settings can influence various parameters, such as network performance for networks and domain propagation.
How Does TTL Work?
When data is sent (for example, HTTP responses or DNS records), it is integrated with a retention time value in seconds. The value you choose in the TTL fields is decremented as the data is kept or used by a system. A value of zero implies that the data living on this system has expired and must be refreshed.
Applications of TTL
- DNS caching: Specifies the amount of time a DNS resolver should store the IP address of a domain name. You can select lower TTL values or higher TTL values based on how long you want the resolver to store the IP address.
- HTTP caching: This helps reduce server load, bandwidth, and page load time. The time-to-live value tells browsers or proxies how long they should store a web response.
- Routing protocols: It keeps data packets from circulating continuously around the internet.
Time-To-Live in DNS & HTTP
- DNS: It defines how long a DNS record (e.g., an A or MX record) is stored by DNS servers. Setting the lowest TTL allows updates to propagate faster and the highest TTL reduces load as the stored information remains for a longer time.
- HTTP: It is also used in headers like Cache-Control or Expires to control the amount of time a browser stores a webpage or resource.
Examples
- A DNS record with a retention time value = 300 will be cached for 5 minutes.
- A browser that stored a CSS file with Cache-Control: max-age=3600 will store it for 1 hour.