An authoritative nameserver is a DNS server that is configured with the records of a zone and answers queries about it from that data, not from a cache. Its replies carry the aa (authoritative answer) flag.
Why it matters
Every lookup ends at an authoritative server. If those servers are down, slow or serving wrong data, nobody can reach your domain once cached answers expire. This is why domains list at least two nameservers, ideally on separate networks. Knowing which servers are authoritative also tells you where to make a change: editing a record at the wrong provider has no effect.
Example
$ dig +norecurse @ns1.example.net www.example.com A
;; flags: qr aa; QUERY: 1, ANSWER: 1
www.example.com. 300 IN A 203.0.113.10The aa flag shows the server answered from its own zone data. A recursive resolver would instead show ra and might return a cached copy.
Common mistakes
- Confusing it with a recursive resolver. Setting 8.8.8.8 as your domain's nameserver does nothing.
- Editing records in a registrar panel while the domain's NS records point to a different DNS host.
- Running a single nameserver or several servers behind the same network, so one outage takes all of them down.
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