DNS propagation

DNS propagation is the process by which changes to a domain's records spread across DNS servers worldwide. After editing a record — for instance pointing a domain to a new server — the update is not instant; it takes time for all servers and devices to start using the new value. This period can last from a few minutes up to 48 hours.

What DNS propagation is

The DNS system is distributed and relies heavily on caching. To offload servers and speed up the internet, intermediate servers and user devices remember DNS answers for a set time. That is why a record change does not reach everywhere at once. The pace of propagation is affected by:

• TTL — the Time To Live value defining how long a record may be cached.
• Resolvers — ISP intermediate servers that store data in cache.
• Type of change — modifying an IP address in an A record or changing the domain's name servers.
• User location — different regions refresh their cache at different rates.

DNS propagation in practice

Awareness of DNS propagation is crucial during several common operations:

1. Changing hosting — moving a site to a new server requires updating the records.
2. Launching a new domain — pointing a domain to the target server after registration.
3. Email migration — changing MX records and the transition window it creates for mail delivery.

To minimise downtime, it is worth lowering the TTL ahead of a planned change and keeping the existing server active throughout the propagation period. That way users who still reach the old location will not see an error until the change has spread globally.