RE: Last Call: draft-klensin-rfc2821bis
John C Klensin <john-ietf@jck.com> Thu, 27 March 2008 22:19 UTC
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Date: Thu, 27 Mar 2008 18:17:22 -0400
From: John C Klensin <john-ietf@jck.com>
To: "Hallam-Baker, Phillip" <pbaker@verisign.com>, alh-ietf@tndh.net, ietf@ietf.org
Subject: RE: Last Call: draft-klensin-rfc2821bis
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--On Wednesday, 26 March, 2008 14:26 -0700 "Hallam-Baker, Phillip" <pbaker@verisign.com> wrote: > > I don't undestand the reasoning here. > > My understanding is that we implicitly deprecated receivers > relying on fallback to A in 2821. We did no such thing. > Section 5 makes it clear > that you look for MX first and that MX takes priority. Yes. And that has been the rule since MX records were introduced, a rule that was reinforced by RFC 1123. This is not news. It has also been the case --since RFC 974, over 22 years ago-- that, if the MX lookup fails, one looks for an A RR. RFC 2821 changed nothing in that regard. People have repeated that to you multiple times. > It is thus not compliant to look at AAAA records today and I > see no reason to change this in the future. This is also not true, but the reason is more subtle. If 2821 said "don't look for an AAAA record and use it as a default" then, certainly, looking for it after the MX lookup failed would not be non-complaint. But it says no such thing. Instead, there is a question of whether the text in 2821 should be interpreted as "look for address records if the MX fails" or "look for a A RR if the MX fails and, if it isn't found, give up". The first interpretation is strongly supported by general advice to implementers of applications to make IPv6 behave as much like IPv4 as possible unless there is a clear reason to not do so. Either interpretation is plausible, and we've got examples of running code that implements the former. There may also be cases of the latter in production servers, but we haven't asked and I don't, personally, know of any. Leaving the ambiguity, long-term, is not reasonable. So 2821bis does what a "bis", and a document going for Draft Standard, is supposed to do, and that is reflect existing practice and clear up ambiguities. Saying nothing is not, IMO, an option. Deprecating the A MX default is not an option. And, given current practice, prohibiting the current default is, IMO, inappropriate unless real harm to the mail system is demonstrated. No one has done that, at least in any message I've read. That current default --both types of address records are available-- is also, by far, the safer one if some implementations assume that the MX is required and others assume that it is not. One could make a different argument, but whether to permit or prohibit using an AAAA record for an MX default is the only question. And we cannot say "MAY" because it would guarantee inconsistent and unpredictable behavior. But, whatever the decision, it is highly constrained. Arguing on the basis of deprecation of a feature that did not occur, or arguing for removal of a function on which many thousands of hosts are depending is, at best, a waste of everyone's time. > Mail is a service lookup, not a host name lookup. Support for > use of fallback to IPv4 host name lookup is a historical > accident due to the fact that the distinction was not > understood at the time. We do not require IPv6 host name > fallback, This, to put it politely, is nonsense. I don't know that I can say anything else without violating IETF list norms for postings. > IPv6 host name fallback has a significant cost that > will have immediate impact on every mail service lookup that > is compliant. No. At most it will have a one DNS lookup impact on mail server lookups that are not associated with MX records. If the sender prefers IPv4 over IPv6, it will have that impact only if there is no A record present and there are some other valid records for the domain name. If the sender prefers IPv6 over IPv4, then it adds nothing. In an IETF that believes the potential recursion of URNs and NAPTR records is reasonable, it is really hard for me to get excited about that one possible extra lookup. YMMD, of course. john _______________________________________________ IETF mailing list IETF@ietf.org https://www.ietf.org/mailman/listinfo/ietf
- RE: Last Call: draft-klensin-rfc2821bis (Simple M… Hollenbeck, Scott
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Pete Resnick
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Dave Crocker
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Ned Freed
- Lists and aliases (Re: Last Call: draft-klensin-r… Harald Tveit Alvestrand
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Pete Resnick
- Re: Lists and aliases (Re: Last Call: draft-klens… Ned Freed
- Re: Lists and aliases (Re: Last Call: draft-klens… Tony Finch
- Re: Lists and aliases (Re: Last Call: draft-klens… Ned Freed
- Last Call: draft-klensin-rfc2821bis (Simple Mail … Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis (Simple M… Pekka Savola
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis Douglas Otis
- Re: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis Mark Andrews
- Re: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis Douglas Otis
- Re: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis John Leslie
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis Douglas Otis
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis Bill Manning
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis Mark Andrews
- Re: Last Call: draft-klensin-rfc2821bis Bill Manning
- Re: Last Call: draft-klensin-rfc2821bis Bill Manning
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis Willie Gillespie
- Re: Last Call: draft-klensin-rfc2821bis Mark Andrews
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Markku Savela
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- RE: Last Call: draft-klensin-rfc2821bis Hallam-Baker, Phillip
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis SM
- Re: Last Call: draft-klensin-rfc2821bis Bill Manning
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Mark Andrews
- Re: Last Call: draft-klensin-rfc2821bis SM
- Re: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis SM
- Re: Last Call: draft-klensin-rfc2821bis Pekka Savola
- Re: Last Call: draft-klensin-rfc2821bis Mark Andrews
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Bill Manning
- Implicit MX and A RRs (was: Re: Last Call: draft-… John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis Mark Andrews
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Implicit MX and A RRs Tony Hansen
- Re: Last Call: draft-klensin-rfc2821bis John Levine
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis Tony Finch
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis John Levine
- Re: Last Call: draft-klensin-rfc2821bis Eliot Lear
- RE: Last Call: draft-klensin-rfc2821bis Tony Hain
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Dave Crocker
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- RE: Last Call: draft-klensin-rfc2821bis Hallam-Baker, Phillip
- Re: Last Call: draft-klensin-rfc2821bis Willie Gillespie
- IPv6 incentive? RE: Last Call: draft-klensin-rfc2… Hallam-Baker, Phillip
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis Jim Fenton
- Re: Last Call: draft-klensin-rfc2821bis David Conrad
- RE: Last Call: draft-klensin-rfc2821bis Tony Hain
- Re: Last Call: draft-klensin-rfc2821bis Dave Crocker
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- RE: Last Call: draft-klensin-rfc2821bis Hallam-Baker, Phillip
- RE: Last Call: draft-klensin-rfc2821bis Tony Hain
- RE: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Implicit MX and A RRs John C Klensin
- Re: Implicit MX and A RRs Matti Aarnio
- RE: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis Mark Andrews
- Re: Implicit MX and A RRs Tony Finch
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis Mark Andrews
- Re: Last Call: draft-klensin-rfc2821bis Joe Abley
- Re: Last Call: draft-klensin-rfc2821bis Mark Andrews
- Re: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis David Morris
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Implicit MX and A RRs Keith Moore
- RE: Last Call: draft-klensin-rfc2821bis michael.dillon
- Re: Last Call: draft-klensin-rfc2821bis Douglas Otis
- Re: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- Re: Implicit MX and A RRs Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis Pekka Savola
- Re: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis Pekka Savola
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis Ned Freed
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Dave Crocker
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Theodore Tso
- Re: Last Call: draft-klensin-rfc2821bis Frank Ellermann
- Re: Last Call: draft-klensin-rfc2821bis Henning Schulzrinne
- Re: Last Call: draft-klensin-rfc2821bis John Levine
- Re: Last Call: draft-klensin-rfc2821bis SM
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis SM
- Re: Last Call: draft-klensin-rfc2821bis John Levine
- Re: Last Call: draft-klensin-rfc2821bis Dave Crocker
- Re: Last Call: draft-klensin-rfc2821bis Henning Schulzrinne
- Re: Last Call: draft-klensin-rfc2821bis David Morris
- Re: Last Call: draft-klensin-rfc2821bis Dave Crocker
- Re: Last Call: draft-klensin-rfc2821bis Mark Andrews
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis John C Klensin
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis Tony Finch
- Re: Last Call: draft-klensin-rfc2821bis Henning Schulzrinne
- Re: Last Call: draft-klensin-rfc2821bis Bill Manning
- Re: Last Call: draft-klensin-rfc2821bis Dave Crocker
- Re: Last Call: draft-klensin-rfc2821bis Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis: closing … Tony Hansen
- Re: Last Call: draft-klensin-rfc2821bis: closing … Dave Crocker
- Re: Last Call: draft-klensin-rfc2821bis: closing … Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis: closing … Lisa Dusseault
- Re: Last Call: draft-klensin-rfc2821bis: closing … Douglas Otis
- Re: Last Call: draft-klensin-rfc2821bis: closing … Hector Santos
- Re: Last Call: draft-klensin-rfc2821bis: closing … Henning Schulzrinne
- Re: Last Call: draft-klensin-rfc2821bis: closing … Dave Crocker
- Re: Last Call: draft-klensin-rfc2821bis: closing … Paul Smith
- Re: Last Call: draft-klensin-rfc2821bis: closing … Keith Moore
- Re: Last Call: draft-klensin-rfc2821bis: closing … Tom.Petch
- Re: Last Call: draft-klensin-rfc2821bis: closing … Hector Santos
- Re: Last Call: draft-klensin-rfc2821bis: closing … Robert A. Rosenberg