Subject: Re: does anybody use additional/authority records on RD/RA replies

From: Rob Austein <[email-masked]>
Date: Sat, 11 Jan 2003 11:40:19 -0500

At Sat, 11 Jan 2003 13:15:40 +0100, bert hubert wrote:
> 
> In a refreshing change, here is a question about DNS.

Thank you!

> I'm wondering if anybody knows of any client library actually using
> additional/authority records in answers to recursion desired/recursion
> available questions, with the exception of the SOA negative presence
> indication.

Additional for sure: think about QTYPE=MX.

Dunno about authority: offhand I can't remember any use for it, but
that doesn't prove that somebody else hasn't got one.

--Rob

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From: bert hubert <[email-masked]>
Date: Sat, 11 Jan 2003 20:12:24 +0100

On Sat, Jan 11, 2003 at 06:33:49PM +0000, Paul Vixie wrote:

> sure.  sendmail's internal getmxrr does this, to try to get the MX and A
> from a single dns transaction.  as far as i know, so does kerberos's 
> internal getsrvbyname.

Thanks, also to Rob. Indeed, I only forgot about that one because my own
boneheaded mailer did not take advantage from that at one point.

But I wonder about the utility of authority in this case - I've already seen
the powerdns recursor, a work in progress, spit out the weirdest things.

An example is www.bibleinfo.org which defines its own NS records with a 10
second TTL. After those are passed, the 'best' NS records are the ORG ones,
which are then attached to the answer, leading to an overly large packet.

[btw, I wonder why the ORG NS records are in COM? Seems silly]

A simple solution to that is not allowing a child to lower the TTL of
existing records, but that does not solve the root issue of the silliness of
adding the 'best' NS records known. Was there a non-human rationale to
adding those?

Regards,

bert

-- 
http://www.PowerDNS.com      Open source, database driven DNS Software 
http://lartc.org           Linux Advanced Routing & Traffic Control HOWTO
http://netherlabs.nl                         Consulting

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From: "D. J. Bernstein" <[email-masked]>
Date: 11 Jan 2003 20:04:42 -0000

> Additional for sure: think about QTYPE=MX.

Clients have to be prepared to ask for A records in a new DNS query. The
MX response often doesn't have any additional data.

It is, of course, safe for a cache to leave out authority and additional
records. dnscache has always done this; BIND 9 can now do it, except for
SOA records, with the ``minimal-responses'' option.

One client---sendmail---tries to skip the A query by caching A records
from the MX response. I'm amused by the ``save network traffic'' excuse
for this complication. If you really care about DNS traffic, why aren't
you running a real DNS cache on the same machine?

---D. J. Bernstein, Associate Professor, Department of Mathematics,
Statistics, and Computer Science, University of Illinois at Chicago

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From: [email-masked]
Date: Sun, 12 Jan 2003 10:32:32 +1100

> Thanks.
> bert hubert

	The update code in libresolv will take advantage of the NS RRset
	if it is there along with the address records in the additional
	section when determining the zone a particular domain name belongs
	to.

	Mark
--
Mark Andrews, Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: [email-masked]

---

From: Michael Milligan <[email-masked]>
Date: Sat, 11 Jan 2003 16:43:10 -0700

> [btw, I wonder why the ORG NS records are in COM? Seems silly]

They are not "in COM" of course... the gTLD servers, which are authoritative 
for com, are also still authoritative for org.  I'm sure that's the case 
only for the transition of org to Afilias, but you never know how long QA 
can take when it comes to the gTLD servers...  ;-)

Side note:  I do find it interesting that a.gtld-servers.net and 
g.gtld-servers.net have TTLs of 172800 (2 days) for the org NS record set 
and the rest of the gTLD servers have 518400 (6 days).

Regards,
Mike

-- 
Michael Milligan  --  Free Agent  --  [email-masked]