DNS: Authoritative name servers

In response to the blog post here on Super User:

When you ask for a response from a name server, that is not found in cache, does it always search for an authoritative response?
Also is an authoritative name server, basically just a name server which is responsible for a zone (i.e. . , com. , superuser.com). Each of those being a zone. Wikipedia is a little unclear on this.

rubixibuc

Posted 2012-02-17T01:20:51.060

Reputation: 1 492

Answers

Regarding question 1: No, not always. Some nameservers will do recursive queries for you, but some only provide answers for zones for which they are authoritative. The global root servers work this way, for instance. Public DNS servers like 8.8.8.8 will do recursive queries for you, however.

Regarding question 2: An authoritative server for a zone is one that has responsibility for the zone, yes. It either knows all information about names in the zone, or it delegates authority about sections of the zone to other servers. For example, ask a root server for an SOA record for example.com and it will provide a list of nameservers for com. Ask one of those servers about example.com and it will provide a list of servers for example.com. Ask one of those servers, and it will provide the SOA record, letting you know that the server is authoritative for the zone, and you can then query that server about names within the zone.

Kyle Jones

Posted 2012-02-17T01:20:51.060

Reputation: 5 706

If I query a recursive server which has a cache, and I ask for a answer which is not cached will it search for and authoritative response, but if query and authoritative for an authoritative answer which it can't provide, can it also give me a cached answer. Are these two real possibilities? Do either make sense? – rubixibuc – 2012-02-17T02:21:56.913

Yes to the first question. The answer to the second question depends on whether the server has been configured to provide answers about zones for which it is not authoritative. If it isn't set up to provide those answers, it likely won't even have a cache. – Kyle Jones – 2012-02-17T03:15:15.287

Recursive queries NEVER addressed to find authoritative source. They just forwarded (if forwarded) to forwarders of /this nameservers/ in order to get answer if they haveb't it locally. And story repeat again, while (any) answer not found
Authoritative name server(s) for any zone(s) is dns-server, which contain local data (not cache) about zones in question. Both Master and Slave DNSes for zone are authoritative, not only mentioned in SOA

Lazy Badger

Posted 2012-02-17T01:20:51.060

Reputation: 3 557