Where is the cache?

[Bob Bernstein]

Barry Margolin <barmar at genuity.net> wrote:

> A forwarding DNS also caches all the answers it gets.  The difference
> between forwarding and non-forwarding is that the latter works its way down
> from the root servers, while the former always sends its queries to the
> ISP's server and lets it do all the hard work.

I wonder if you would be good enough to clarify the meaning of the term
"always" in the above statement? I see that the 'forward' option can take
either 'only' or 'first' as an argument, and that suggests the possibility
that, if the 'forward first' option is used, then a query attempt sent first
to the forwarders might then be redirected by the local nameserver directly
to the root server tree.

I find myself imagining a scenario in which the root servers might be
queried *if*, upon being consulted, the forwarders are found to have no
Non-authoritive answers. In other words, when queried as forwarders do they
attempt their own search of the root server tree and return that information
if it's not in their cache?

> A month or two I wrote a message that tried to explain the pros and cons of
> the two approaches in more detail.

Thanks, I'm off to deja right now.

-- 
Bob Bernstein                     http://www.ruptured-duck.com