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Date:      Mon, 20 May 2002 19:15:46 +0300
From:      Peter Pentchev <roam@ringlet.net>
To:        Damon Anton Permezel <dap@damon.com>
Cc:        freebsd-qa@FreeBSD.org, freebsd-hackers@freebsd.org
Subject:   Re: 4.6-* sendmail misfeatures
Message-ID:  <20020520191546.D349@straylight.oblivion.bg>
In-Reply-To: <20020520105154.E962@damon.com>; from dap@damon.com on Mon, May 20, 2002 at 10:51:54AM -0500
References:  <20020520105154.E962@damon.com>

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On Mon, May 20, 2002 at 10:51:54AM -0500, Damon Anton Permezel wrote:
> Since upgrading from 4.5 to 4.6-*, I have had problems exchanging
> email with a correspondent at "austinenergy.com".  It shows up as:
>=20
> 	% echo hi | mail -v no.such.user@austinenergy.com
> 	austinenergy.com: Name server timeout
> 	no.such.user@austinenergy.com... Transient parse error -- message queued=
 for future delivery
> 	no.such.user@austinenergy.com... queued
>=20
> I have tracked this down to the fact that sendmail is using a IPv6-style
> lookup request.  It is a "AAAA ?" rather than a "A ?" (in tcpdump-esque).

[CC'd to -qa; this seems to be a usability problem, we are in a release
 code freeze, which mostly makes it a QA problem.]

What exactly is the tcpdump output that you have been getting?
It seems to me that, at least from my end, it is a simple matter
of a timeout - the nameserver for austinenergy.com is listed
from the gTLD servers as bolt.electric.austin.tx.us, and the nameservers
for electric.austin.tx.us seem to not reply to any requests at all:
nslookup, dig, dnsip, dnsipq all return either a timeout or
a 'connection refused', which is mostly synonymous to a timeout.

The fact that you see an AAAA query from sendmail is due to its (correct)
behavior of trying an AAAA query before an A one, so as to prefer an IPv6
AAAA record to an IPv4 A record.  The fact that sendmail does not even
try an A query is due to its (correctly) assuming that something is wrong
with the server - temporarily - because it received a SERVFAIL response.
The SERVFAIL response (which means exactly as it says, a server failure,
which is assumed to be a temporary condition) is returned by either your
FreeBSD system's resolver library, or your ISP's nameserver, simply
because, well, because the server failed (see above about the timeouts).

> Further investigation dug up this manifesto in the sendmail README:
>=20
> 	When attempting to canonify a hostname, some broken name
> 	servers will return SERVFAIL (a temporary failure) on T_AAAA
> 	(IPv6) lookups.  If you want to excuse this behavior, include
> 	WorkAroundBrokenAAAA in ResolverOptions.  However, instead,
> 	we recommend catching the problem and reporting it to the
> 	name server administrator so we can rid the world of broken
> 	name servers.
>=20
> So, in violation of the networking "be liberal in what you accept and
> conservative in what you produce", sendmail in it's new form will have ma=
ny
> perplexed sysadmins spending lots of time tracking down these mysterious
> failures.
>=20
> I suggest that the version of sendmail configs shipped with FreeBSD
> should default to having WorkAroundBrokenAAAA set by default.

Just a question: have you tried it with this option, and did it work?
That is, did you get a response to an A query that you did not get
to an AAAA?  Once again, can you post some tcpdump output?

G'luck,
Peter

--=20
Peter Pentchev	roam@ringlet.net	roam@FreeBSD.org
PGP key:	http://people.FreeBSD.org/~roam/roam.key.asc
Key fingerprint	FDBA FD79 C26F 3C51 C95E  DF9E ED18 B68D 1619 4553
This sentence contradicts itself - or rather - well, no, actually it doesn'=
t!

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