General DNS questions

[Kevin Darcy]

hank at interall.co.il wrote:

> I hope this won't be considered too newbie.
>
> q1: Can a dns plain host's resolver (not  a name server) ask for an
> iterative query at all or does it ALWAYS count on the server to do it?

I'm not sure I quite understand the question. System resolvers (usually accessed
via gethostbyname() or gethostbyaddress()) will issue recursive queries. But
programs with their own embedded resolvers, e.g. dig or nslookup, often provide
an option for non-recursive queries.

> How wide is the usage of such hosts in the real world?

You mean, hosts whose system resolvers allow toggling of
recursive-versus-non-recursive? I would say "very low usage", since I'm not aware
of any OS that implements this.

> q2: A name server is supposed to track down an answer itself and not be asking
> other name servers recursive queries. Is it applicable to define a name
> server as non-recursive for hosts (and name servers) located outside the
> autonomous system?

You mean, serve zones to external clients non-recursively? This is very common,
and in fact recommended. Note however that if you want the same box to operate
recursively for internal clients (to resolve Internet names) and non-recursively
for external clients, you may have to do some fancy configuration work, and
external clients may still get non-authoritative answers from you because named
will still answer from its cache even when it is not honoring recursion for a
particular client. The best thing of all is to split recursive and non-recursive
function into separate nameserver machines, or separate nameserver instances
running on the same machine. Such a functional split can have scalability/tuning
benefits also, since *pure* non-recursive servers experience no cache growth.

> q3: When will a resolver ask for more then one query in the same packet?

When it's corrupted or braindamaged?

Multiple queries per packet is not currently standards-compliant, as far as I am
aware (yes, I know about the EDNS1 proposal, but that's dead now isn't it?).


- Kevin