A name server indicates that its response is authoritative by setting the Authoritative Answer (AA) bit in the response to a query on a name for which it is authoritative. Name servers providing answers for which they are not authoritative (for example, name servers for parent zones), Caching name servers, also called DNS caches, store DNS query results for a period of time determined in the configuration (time-to-live) of each domain name record. DNS caches improve the efficiency of the DNS by reducing DNS traffic across the Internet, and by reducing load on authoritative name servers, particularly root name servers. Because they can answer questions more quickly, they also increase the performance of end-user applications that use the DNS.A domain is registered with a domain name registrar, the zone administrator provides a list of name servers (typically at least two, for redundancy) that are authoritative for the zone that contains the domain. The registrar provides the names of these servers to the domain registry for the top level domain containing the zone. The domain registry in turn configures the authoritative name servers for that top level domain with delegations for each server for the zone. If the fully qualified domain name of any name server for a zone appears within that zone, the zone administrator provides IP addresses for that name server, which are installed in the parent zone as glue records; otherwise, the delegation consists of the list of NS records for that zone.