A name server in the Domain Name System (DNS) that can resolve name lookup requests but does not maintain its own local DNS database or zone file of resource records.
Caching-only name servers do not have their own DNS databases. Instead, they resolve name lookup requests from resolvers by making iterative queries to other name servers. Once the responses to these queries are received, they are cached by the caching-only name server, in case another resolver issues the same request within a short period of time.
A caching-only name server is not authoritative for any particular DNS domain. It can look up names that are inside or outside its own zone.
Caching-only name servers aren’t the only kind of name server that performs caching of resolved queries. For example, primary name servers also cache name lookups that they perform. This caching generally improves the response of the primary name server to name lookup requests from resolvers. Caching-only name servers are distinguished by the fact that they perform only one function: issuing iterative queries to other name servers and then caching the results.
Caching-only name servers provide support for primary and secondary name servers in environments where name lookup traffic is heavy. Using caching-only name servers where possible also reduces the overhead of zone transfers between name servers on a network.