What is an authoritative DNS server? What is a recursive DNS server?

A DNS name server is anything serving DNS responses to DNS requests. But there are two kinds of name servers out there: authoritative name servers and recursive name servers. Authoritative name servers don’t need to consult any higher authority to serve their responses; they are the ultimate authority on the domains they are serving responses about. Conversely, recursive name servers serve their responses by consulting higher authorities; the recursive name servers are useful because they cache those responses and reduce the load on authoritative servers. The recursive name servers are a sort of global CDN for the DNS.

Name servers can be authoritative and recursive, but they broadly fall into those two categories. For examples:

A way to check whether a name server is authoritative is to query it for a common domain, e.g.

$ dig @ google.com.

; <<>> DiG 9.8.3-P1 <<>> @ google.com.
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 20137
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 13, ADDITIONAL: 14
;; WARNING: recursion requested but not available

Notice that dig says “recursion requested but not available”. The server at is therefore an authoritative name server only.