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I know the semantics don’t sound right, but I just came up with this question.

Let’s say a client queries a DNS server for www.example.com, which recursively asks the root server, then the TLD, then example.com until the IP is found. Then this DNS server would store the IP in its cache.

Since I’ve read that:

“…an authoritative nameserver is one that satisfies queries from its own data without needing to reference another source…”

Would this cached information make the DNS server authoritative for www.example.com? I know the answer is probably “no” but I can’t figure out the exact reason.

I’ve also read that a server can serve authoritative data for a zone which is not delegated to them, which is what arose my question.

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Would this cached information make the DNS server authoritative for www.example.com? I know the answer is probably “no” but I can’t figure out the exact reason.

No. Why would it be authoritative if the information is cached? An authoritative DNS server would be one in which the DNS info stored can only be changed by the owner of that DNS entry data. Even if two servers contain the same exact information in every superficial respect, the non-authoritative servers are ultimately subordinate to where it gets the data it stores from.

Meaning, if a DNS server can have it’s cache cleared or altered just by a simply DNS query—and not an authoritative change—then it can never be authoritative.

  • That was the bit of information I was missing. Thank you! – Floella Jun 20 '16 at 22:36
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You read/quoted an oversimplified description of what an authoritative name server is.

The DNS system keeps track of which name servers are authoritative for any given domain. The root servers are authoritative for the top-level domains (e.g. .com, .net), and refer you to the authoritative name servers for the second level domains (e.g. they might tell you ns.example.com is authoritative for example.com).

The authoritative name servers for a second-level domain could refer you to an authoritative name server for a subdomain, if any (e.g. ns1.sub.example.com for sub.example.com), and so on.

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