Forum Thread: Why Can't I Get an Authoritative Answer from a Domain Name?

This may be wrong as its too early to grab my notes, but i'm certain Authoritative is when you nslookup a domain which isn't already cached, and non authoritative occurs when the address you are looking for has already been cached, allowing us to retrieve the information faster. Hope this helps.

I was close, mb :

"The answer you've received is essentially a cached or forwarded response from your local DNS server. Basically, a non-authoritative name server is one that does not contain the records for the zone being queried; your local DNS is likely not going to have Google's name records"

Codered is on the right track. It's when a response comes from a name server that's not "authoritative" over that domain. Try these string of commands and see for yourself. In a nutshell, you can only get an authoritative response from one of the name servers explicitly living in your zonefile.

nslookup
google.com
set q=ns
google.com
server 216.239.32.10
google.com

What we're doing is looking up the A record for google.com, then we're setting the query to see the nameservers (NS records) of the domain. Then we set nslookup to query that name server directly. Then we ask for the A record again and no "non-authoritative" response.