What Is DNS Propagation and Why Do You Have to Wait?
When you change a record, why does everyone not see it at once? The role of caching, TTL and propagation testing.
What is propagation?
DNS changes are not held in a single place; they spread to tens of thousands of resolvers around the world. Each resolver keeps the old record in cache for the TTL duration. That is why changes appear gradually rather than instantly.
Why do results differ?
- Resolvers run in different geographic locations; anycast routing may return different IP addresses.
- Some resolvers apply filtering.
- Resolvers whose cache has not expired return the old value.
The right expectation
For name server changes, 24-48 hours of propagation is normal, while for simple A/MX updates it ranges from minutes to hours depending on the TTL. Lowering the TTL before a migration shortens the time.
What does a propagation test show?
NetQuery queries the same record across 16 different countries and 6 resolvers, comparing where the new value has and has not appeared. It is also used to verify that CDN and anycast deployments are working correctly.
Summary
Plan your TTL, be patient, and use a propagation test to verify the result.