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Re: deprecating Postel's principle- considered harmful

Joe Touch <touch@strayalpha.com> Wed, 08 May 2019 04:17 UTC

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Subject: Re: deprecating Postel's principle- considered harmful
From: Joe Touch <touch@strayalpha.com>
In-Reply-To: <CALaySJJDHg5j9Z7+noS=YXoNROqdsbJ6coEECtLtbJ6fWJ3xsQ@mail.gmail.com>
Date: Tue, 07 May 2019 21:17:27 -0700
Cc: "BRUNGARD, DEBORAH A" <db3546@att.com>, The IESG <iesg@ietf.org>, "iab@iab.org" <iab@iab.org>, "architecture-discuss@ietf.org" <architecture-discuss@ietf.org>, "ietf@ietf.org" <ietf@ietf.org>
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To: Barry Leiba <barryleiba@computer.org>
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> On May 7, 2019, at 1:29 PM, Barry Leiba <barryleiba@computer.org> wrote:
> 
>> It just erroneously blames Postel for sloppy implementations.
> 
> Blaming the principle isn't the same as blaming Postel; the point here
> isn't so much that "Postel was wrong" as it is that there are many
> consequences of adhering to that principle that Jon didn't anticipate.

I’ve already noted this in earlier versions of this thread, but to restate:

Protocols are, by definition, a set of rules - rules for BOTH sender and receiver - that enable communication (sharing of state) [Shannon/Weaver]. 

The point of the Postel Principle is to stay INSIDE the lines as a sender, and allow right up to the lines for the receiver.

It is about interpreting the (often unavoidable) aspects of protocol that are ambiguous.

*NONE* of it is about tolerating bugs or errors, nor is it about allowing arbitrary behavior for senders. 

It can’t be - again, protocols are rules. Take away the rules and you take away the ability to communicate.

Joe

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