Caching-Only Behavior

[Kevin Darcy]

Joe Kattner wrote:

> Jeff,
>
> If the name server is set up as caching only, other servers will not
> ever send it queries (unless it's acting as a forwarder, but you don't
> mention that). It must be authoritative for something so another server
> would know that it exists and needs to query it. In you example the name
> server is not authoritative for anything, so the description you give in
> the last paragraph is accurate; Caching servers work for the clients,
> and reduce the load on authoritative servers.
>
> Clients on the other hand must be configured to send their DNS queries
> to specific name server(s). The server then uses recursion to find the
> answers for those clients. Your example server holds no answers, only
> the ability to perform a recursive query for it's clients.
>
> --Joe
>
> -----Original Message-----
> From: NCR Employee [mailto:ncremployee at ncr.com]=20
> Sent: Wednesday, November 20, 2002 10:11 AM
> To: comp-protocols-dns-bind at isc.org
> Subject: Caching-Only Behavior
>
> I have not been able to find any reference material to answer my DNS
> question:
>
> When a UNIX system is properly setup to perform caching and it is not
> setup as a Primary or Secondary Nameserver, will it respond to name
> server requests that are sent directly to it from other servers?
>
> I would think that name caching was used on the local host to speed up
> name resolution for local applications and to minimize requests to the
> actual DNS server, rather than, providing name resolution for other
> servers.

Perhaps it would be worth emphasizing that when a zone is delegated to a
nameserver, other nameservers following that delegation will a) send
*non-recursive* queries to it, and b) will expect authoritative responses
(i.e. for the AA bit to be set in the responses). Unless the caching server
coincidentally happens to have the answer in its cache, it won't be able to
answer a non-recursive query, and, in any case, even if does answer from
its cache, the answer will not be authoritative, so the requesting server
may mark it as "lame".

So, the bottom line here is that it doesn't really work to delegate a zone
to a caching-only server (although some domain moochers have been known to
do that, rather than cough up a couple of authoritative nameservers of
their own).


- Kevin