Caching, TTL, and DNS Issues
See how caching speeds lookups and how stale records cause trouble.
Why Caching Exists
Querying the full DNS hierarchy for every lookup would be slow and would overload the servers. Caching stores recent answers so repeated lookups are instant.
Resolvers, operating systems, and even browsers keep DNS caches. Caching is what makes DNS fast and scalable across billions of daily queries.
What TTL Controls
Each DNS record carries a TTL (Time To Live), a number of seconds telling caches how long to keep the answer before it expires.
A record with a TTL of 3600 can be cached for one hour. After the TTL elapses, the cache discards the entry and must look it up fresh next time.
example.com A 93.184.216.34 TTL 3600All lessons in this course
- Why DNS Exists
- Walking Through a DNS Lookup
- Common DNS Record Types
- Caching, TTL, and DNS Issues