RE: deprecating Postel's principle- considered harmful

"BRUNGARD, DEBORAH A" <> Tue, 07 May 2019 19:18 UTC

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Subject: RE: deprecating Postel's principle- considered harmful
Thread-Topic: deprecating Postel's principle- considered harmful
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Date: Tue, 7 May 2019 19:17:58 +0000
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Not seeing much discussion on this document on the lists, I put a twist on the title-

I find the document (as currently written) is incorrectly interpreting the robustness principle as saying there is no need for clear rules on protocol evolvability/extensions. For example, section 6, "relying on implementations to consistently apply the robustness principle is not a good strategy for extensibility". In the routing area, we do have rules and we use the principle to ensure interoperability, as we don't have the luxury to do a "forklift". Section 8's "it is not always possible to produce a design that allow all current protocol participants to continue to participate", my question would be "but does it harm the network"?

Actually most of the document confusingly is not contradicting Postel's principle but supporting it (except for the nuances which seem to condone forklifts). It just erroneously blames Postel for sloppy implementations. For the document to summarize saying "the robustness principle can, and should, be avoided" as it is harmful (I think) will be harmful to the Internet.

Hopefully more folks will read it-
(probably discussion is more appropriate on the architecture-discuss list)

-----Original Message-----
From: IAB <>; On Behalf Of
Sent: Monday, May 06, 2019 10:40 PM
Subject: [IAB] I-D Action: draft-iab-protocol-maintenance-03.txt

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Internet Architecture Board IETF of the IETF.

        Title           : The Harmful Consequences of the Robustness Principle
        Author          : Martin Thomson
	Filename        : draft-iab-protocol-maintenance-03.txt
	Pages           : 11
	Date            : 2019-05-06

   Jon Postel's famous statement of "Be liberal in what you accept, and
   conservative in what you send" is a principle that has long guided
   the design and implementation of Internet protocols.  The posture
   this statement advocates promotes interoperability in the short term,
   but can negatively affect the protocol ecosystem over time.  For a
   protocol that is actively maintained, the robustness principle can,
   and should, be avoided.

The IETF datatracker status page for this draft is:

There are also htmlized versions available at:

A diff from the previous version is available at:

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