Negative Caching (NXDOMAIN)
Negative caching is the storage of negative DNS responses — most commonly NXDOMAIN ("Non-Existent Domain") and NODATA answers — by [[recursive-dns|recursive resolvers]], as defined in RFC 2308. When a resolver queries for a domain that does not exist and receives an NXDOMAIN response, it caches this negative result for the duration specified in the [[soa-record|SOA record's]] minimum TTL field, preventing repeated upstream queries for the same non-existent name. Negative caching reduces load on [[authoritative-dns|authoritative servers]] during typo storms or targeted query floods. The negative [[ttl|TTL]] is typically shorter than positive record TTLs, commonly set between 60 and 3600 seconds.
Example
If a resolver queries for mispeld.example.com and receives NXDOMAIN, it caches that negative answer for the SOA minimum TTL (e.g., 300 seconds), returning the cached NXDOMAIN instantly to any client asking for the same name within that window.