cache server with authoritative answer

[Kevin Oberman]

On Sat, 2011-01-29 at 14:49 +0800, pyh at mail.nsbeta.info wrote:
> The book "Pro DNS and BIND" says: 
> 
> If the caching server obtains its data directly from an authoritative DNS, 
> then it too will respond as authoritative. Ohterwise, if the data is 
> supplied from its cache, the response is nonauthoritative. 
> 
> So this means even for a cache only server it can answer with authoritative 
> response? I have been thinking the cache only server shouldn't do this. 
> 
> Regards.
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If the caching-only server does not have an answer to a query in its
cache and recurses and gets an authoritative response, it, too, will set
the AA bit. If it gets another query for the name that is now cached,
the AA bit will not be set. Further, if any host responding to a query
already has the information in cache, the AA bit will not be set.

In simple terms, if the response to a query comes directly from
information at an authoritative source, the AA bit is set.