Why DNS caches
DNS caching reduces repeated queries to authoritative infrastructure and makes common lookups faster. A recursive resolver can answer a client directly when it has a valid cached record.
TTL behavior
TTL defines how long a cached DNS answer may be reused. A long TTL improves cache efficiency but slows visible changes; a short TTL makes updates appear sooner at the cost of more frequent upstream resolution.
Multiple cache layers
DNS information can be cached at more than one layer: the browser or operating system, local networks, recursive resolvers, and intermediate services. Those layers can expire at different times.
As a result, two clients can temporarily observe different answers even when they are querying the same domain.
Propagation and troubleshooting
When a record changes, first verify the authoritative answer, then compare responses from independent recursive resolvers. This separates an authoritative configuration problem from a cache that has not expired yet.
| Check | Question |
|---|---|
| Authoritative server | Is the intended record published at the source? |
| Multiple resolvers | Are different recursive providers returning the same answer? |
| Local client | Could the browser, OS, router, or local resolver still have an older cache? |