Understand TTL and DNS propagation time

This guide describes the meaning of TTL, abbreviation for "Time To Live" and the principle of time limits DNS propagation, concepts important in the operation of domain name services.

Preamble

• The TTL determines how long the DNS information is cached before being updated.
• This directly influences the speed of propagation of DNS changes across servers around the world.
• Although the reduction of TTL can accelerate the spread, ISP behaviour and caches can introduce additional delays.

The TTL (Time to Live)

The TTL (Time to Live) is a key parameter in managing DNS records. It represents the duration, expressed in seconds, during which DNS information can be stored in cache before being updated. When a DNS server or Internet Service Provider (ISP) queries a DNS area, it temporarily keeps the responses obtained in order to reduce the burden on servers and speed up navigation for users.

P.e. if the TTL is set at 24 hours (86400 seconds), the DNS information relating to a domain will be cached and will not be updated during this period, even if you have changed settings like the IP address of the domain. This means that the DNS changes will only take effect after this deadline has expired.

It is possible to speed up the implementation of the changes by reducing the TTL before making updates. P.ex lowering the TTL to one hour (3600 seconds) allows DNS servers to check new information faster after a change.

DNS propagation

The TTL is directly linked to the TTL process. DNS propagation DNS propagation is the time required for changes to a DNS area to be disseminated to all DNS servers around the world. This delay depends not only on the TTL that is configured, but also on how ISPs and other DNS servers manage their caches.

When editing DNS records, DNS and FAI servers must wait until the TTL delay expires before retrieving the new information. Thus, the shorter the TTL, the faster the changes spread across the network. However, some ISPs sometimes ignore the duration of the TTL and keep the information in cache for a longer period (e.g. 24 hours or more), which can slow the spread of DNS changes, even if you have configured a reduced TTL.