The Harmful Consequences of the Robustness Principle
draft-iab-protocol-maintenance-03
Network Working Group M. Thomson
Internet-Draft Mozilla
Intended status: Informational May 07, 2019
Expires: November 8, 2019
The Harmful Consequences of the Robustness Principle
draft-iab-protocol-maintenance-03
Abstract
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.
Status of This Memo
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This Internet-Draft will expire on November 8, 2019.
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Internet-Draft Protocol Maintenance May 2019
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Fallibility of Specifications . . . . . . . . . . . . . . . . 3
3. Protocol Decay . . . . . . . . . . . . . . . . . . . . . . . 4
4. Ecosystem Effects . . . . . . . . . . . . . . . . . . . . . . 5
5. Active Protocol Maintenance . . . . . . . . . . . . . . . . . 6
6. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 7
7. The Role of Feedback . . . . . . . . . . . . . . . . . . . . 8
7.1. Feedback from Implementations . . . . . . . . . . . . . . 8
7.2. Virtuous Intolerance . . . . . . . . . . . . . . . . . . 8
8. Risk of Exclusion . . . . . . . . . . . . . . . . . . . . . . 9
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
11. Informative References . . . . . . . . . . . . . . . . . . . 10
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Jon Postel's robustness principle has been hugely influential in
shaping the design of the Internet. As stated in IAB RFC 1958
[PRINCIPLES], the robustness principle advises to:
Be strict when sending and tolerant when receiving.
Implementations must follow specifications precisely when sending
to the network, and tolerate faulty input from the network. When
in doubt, discard faulty input silently, without returning an
error message unless this is required by the specification.
This simple statement captures a significant concept in the design of
interoperable systems. Many consider the application of the
robustness principle to be instrumental in the success of the
Internet as well as the design of interoperable protocols in general.
Time and experience shows that negative consequences to
interoperability accumulate over time if an implementations apply the
robustness principle. This problem originates from an assumption
implicit in the principle that it is not possible to affect change in
a system the size of the Internet. That is, the idea that once a
protocol specification is published, changes that might require
existing implementations to change are not feasible.
Many problems that might lead to applications of the robustness
principle are avoided for protocols under active maintenance. Active
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