Re: ns delegation, unix dig vs dnsjava dig vs dnsjava Lookup

[Brian W. <bwe...@xb...>]

On Wed, 18 Jul 2007, Stefano Bagnara wrote:

>> Something's very strange here.  Both the standard unix dig and dnsjava's
>> dig default to recursive queries - this can be been by the fact that
>> both answers have the RD (recursion desired) bit set.  For some reason,
>> only the answer from dnsjava's dig has the RA (recursion available) bit
>> set. I'm seeing the same responses, but I can't think of any good reason
>> why that would happen.
>>
>> I tried adding the +qr option to the standard dig, and the -q option to
>> dnsjava's dig, which causes the queries to be printed as well as the
>> responses, but all that shows is that the queries are identical (except
>> for query id).
>>
> So this is more weird than I thought :-/
>
> After more "digging" ;-) I think I found a bug in dnsjava dig. If you
> call it without the full type/class specification (MX IN at the end and
> some more ignored parameters) then it throws a silently caught
> ArrayIndexOutOfBoundException while processing arguments. This way it
> never sets the server and will use your default server :-). So I think
> this is a bug you can easily fix in your dig. Once you fix that bug or
> simply add "MX IN -q somethingelse" the results are different:

Good catch.  Yes, that looks like a problem.

> Now, back to my problem I have another domain that currently reproduce
> the previous behaviour (even if this time the 2 dig results are equals):
>
> [snip]
>
> You say that dig defaults to recursive queries. Instead dnsjava Lookup
> does not support recursive resolution, right?

The terminology you're using here is a bit confusing.  The standard unix 
dig, dnsjava's dig program, and the dnsjava Lookup class all behave the 
same way - they set the recursion desired bit on queries, meaning that 
they are requesting that the server perform a recursive lookup.  None of 
them performs recursive resolution themselves.

> We use dnsjava to lookup MX records for SMTP delivery: what do you think
> is the behavior required by DNS+SMTP specification? Currently we simply
> run the Lookup using the dnsservers configured by the user (or the one
> autodiscovered by dnsjava) and take its result as is. In this
> "uudial.ch." domain and 194.246.118.118 configuration the dnsjava
> "Lookup" does not return the MX record: is this intended? Should we do
> something different? Can you answer this or give me a pointer to some
> doc I can read about?

I don't know what 194.246.118.118 is, but when I query it, it's not doing 
recursion.  dnsjava's Lookup class is a stub resolver, so it should only 
be sending queries to servers that perform recursion.  If I instead send 
the query to a server that does perform recursion, I get the desired MX 
record.

Brian