Authoritative Nameserver

An authoritative nameserver is the server that holds the original DNS records for a domain in its zone file. When a recursive resolver chases a query down through the DNS hierarchy (root, then TLD, then domain), the answer it ultimately reaches comes from the authoritative nameserver for that domain. Authoritative responses set the AA flag in the DNS reply, signalling that the data is canonical rather than cached. If a domain's authoritative nameservers go down or return wrong data, the domain effectively disappears from the internet. Most domains run at least two authoritative nameservers for redundancy.