Where is the cache?

[Barry Margolin]

In article <zpUY4.65997$MZ2.701698 at news1.wwck1.ri.home.com>,
Bob Bernstein  <PooBah at ruptured-duck.com> wrote:
>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.

It will revert to the normal behavior (following NS records from the root
servers) if the ISP's server doesn't respond.

>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?

When "forwarders" is used, the forwarding server sends its queries with the
"recursion desired" option enabled, so the ISP's server is supposed to
attempt its own search from the root servers.  The forwarding server will
accept non-authoritative answers.


-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
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