From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <0bfd32bfe8981a44d7e61aa8de388107@coraid.com>
From: erik quanstrom <quanstro@coraid.com>
Date: Tue, 16 Jan 2007 14:05:05 -0500
To: 9fans@cse.psu.edu
Subject: Re: [9fans] $smtp dns failure
In-Reply-To: <ee9e417a0701161044i5fc77ddfrbfa3585f3cd91036@mail.gmail.com>
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=C2=A75 of rfc 2821 spells out how to do the lookup.  smtpd should do tha=
t.
if there are any huristics to apply while running the lookup, it
would make sense to me to do as sendmail/postifix/qmail do.
smtp is an interface to the world.  being different isn't a virtue
in this case.

- erik

On Tue Jan 16 13:46:09 EST 2007, rsc@swtch.com wrote:
> > there is an interesting case  with mxlookup1() in mxdial.c.
> > if a dns /failure/ is reported for the mx lookup, then mxdial doesn't
> > try a/cname records.  i've had trouble in the past with mx failures w=
hen the
> > a record looks up just fine.  i'm not sure if the standard says one m=
ust quit
> > on dns failure.
>=20
> if there is a dns failure, the logic there is that since the
> mx could not be determined due to some transient dns error,
> we are not going to blindly try the underlying host name,
> because that is likely to be wrong.  i am sure that i put this
> in because of actual problems.
>=20
> the real problem is that smtp is doing a dns lookup on 192.168.0.22,
> which ndb/dns interprets as a request for a reverse lookup
> (that is, it looks up 22.0.168.192.in-addr.arpa), which fails.
> mxlookup should probably check whether ds->host is a
> valid ip address all by itself, and then return 0 if so, rather
> than ask dns anything at all.  unfortunately i don't think there
> is a library routine that will tell us whether a string is a valid
> ip address.  parseip doesn't.
>=20
> russ