Re: [dmarc-ietf] Concerns about Oldest-Pass (was: Last Call: <draft-ietf-dmarc-arc-protocol-18.txt>...)

"Murray S. Kucherawy" <superuser@gmail.com> Mon, 05 November 2018 04:54 UTC

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From: "Murray S. Kucherawy" <superuser@gmail.com>
Date: Mon, 5 Nov 2018 13:54:33 +0900
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To: Scott Kitterman <sklist@kitterman.com>
Cc: "<kboth@drkurt.com>" <kurta@drkurt.com>, IETF DMARC WG <dmarc@ietf.org>
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Subject: Re: [dmarc-ietf] Concerns about Oldest-Pass (was: Last Call: <draft-ietf-dmarc-arc-protocol-18.txt>...)
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Given the intended status is Experimental, is this something that's a
showstopper?

We have the debate about "fail" versus "invalid" that I believe we consider
to be a showstopper for Proposed Standard, but we're willing to let slide
for Experimental.  Is this the same?

-MSK

On Mon, Nov 5, 2018 at 1:13 PM Scott Kitterman <sklist@kitterman.com> wrote:

>
>
> On November 5, 2018 3:35:23 AM UTC, Kurt Andersen <kurta@drkurt.com>
> wrote:
> >Taking this back to the dmarc list instead of the IETF-wide one:
> >
> >On Wed, Oct 31, 2018 at 1:41 AM Scott Kitterman <scott@kitterman.com>
> >wrote:
> >
> >> . . .  I understand the desire to just ship it at this point so more
> >> operational experience can be gained before another update.  With one
> >> exception, I agree with that approach.
> >>
> >> In Section 5.2.  Validator Actions, I think it's highly unlikely that
> >Step
> >> 5, AMS (ARC Message Structure) validation of AMS header fields beyond
> >the
> >> one immediately prior in the chain is useful.
> >>
> >> Failure doesn't change the ARC result, so there are no
> >interoperability
> >> implications for removing it from the draft.  The only reason to
> >specify
> >> anything is the notion of 'oldest-pass'.  This looks like a dubious
> >and
> >> premature optimization to me.
> >>
> >> I didn't and don't plan to implement it.
> >>
> >> Later, after there is more experience with ARC, if it's established
> >that
> >> validation of AMS beyond the immediately prior step in the chain has
> >> utility and there is sufficient efficiency associated with
> >'oldest-pass',
> >> it can be added then.  'Oldest-pass' seems like an easy way to get
> >around
> >> having downstream validators do AMS validation up the chain (by
> >always
> >> adding arc.oldest-pass=1 to all messages).
> >>
> >> ARC is complicated enough without this and it seems like any easy win
> >for
> >> simplicity in design to take this out for now (and we'll see about
> >the
> >> future).  Deleting it also reduces the IANA considerations.
> >>
> >
> >I'm not by any means arguing with your analysis and plans to skip this
> >component, but I did want to point you, for informational purposes to
> >the
> >WG thread which was the genesis of this concept. It was originally
> >proposed
> >as "closest-fail" but then inverted to be "oldest-pass". You can find
> >the
> >thread from January 2018 at
> >https://mailarchive.ietf.org/arch/msg/dmarc/_sG6ECCBfT5OPQ0LkDThzcGPHGI
> >which references an older discussion circa August 2017.
>
> Thanks.  I've reviewed it and my opinion is reinforced.  It ought to be
> removed.  Nothing other than the immediate prior AMS matters for evaluation
> of the ARC result.  Everything about prior hops is purely for receiver
> edification, not needed for the protocol.
>
> Scott K
>
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