[84961] in North American Network Operators' Group
Re: Weird DNS issues for domains
daemon@ATHENA.MIT.EDU (John Dupuy)
Thu Sep 29 14:11:42 2005
Date: Thu, 29 Sep 2005 13:08:50 -0500
To: Todd Vierling <tv@duh.org>
From: John Dupuy <jdupuy-list@socket.net>
Cc: nanog@nanog.org
In-Reply-To: <Pine.NEB.4.63.0509291326390.8521@server.duh.org>
Errors-To: owner-nanog@merit.edu
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<font size=3>I'll defer to you on this. Clearly a failure to resolve is
not the same thing as a NXDOMAIN RCODE.<br><br>
And yet, personal experience has show that the failure of all a
customer's DNS servers for a domain does cause swifter mail bouncing than
would occur otherwise. I do not know if it was due to the other providers
having broken MTAs or broken DNS servers/resolvers... Or maybe they were
all flukes. I now wish I had investigated them more thoroughly for the
few times I've seen it.<br><br>
John<br><br>
At 12:29 PM 9/29/2005, Todd Vierling wrote:<br><br>
<blockquote type=cite class=cite cite>On Thu, 29 Sep 2005, John Dupuy
wrote:<br><br>
> If you are talking about strictly http, then you are probably right.
If you<br>
> are hosting any email, then this isn't the case. A live DNS but dead
mail<br>
> server will cause your mail to queue up for a later resend on the
originating<br>
> mail servers. A dead DNS will cause the mail to bounce as
undeliverable.<br><br>
If a mail server is bouncing immediately on a DNS SERVFAIL (which is
what<br>
you'll get when a remote DNS server is down), then that mail server is
badly<br>
broken and will break quite a bit during tier1 failure
situations.<br><br>
Failure to resolve != resolves to NXDOMAIN/empty. A failure to
resolve<br>
(SERVFAIL) should result in the same queueing behavior that the remote
SMTP<br>
server uses for failure to establish a TCP connection.<br><br>
-- <br>
-- Todd Vierling <tv@duh.org> <tv@pobox.com>
<todd@vierling.name> </font></blockquote></body>
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