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The Harmful Consequences of the Robustness Principle

The information below is for an old version of the document.
Document Type Expired Internet-Draft (iab)
Author Martin Thomson
Last updated 2020-05-06 (Latest revision 2019-11-03)
Replaces draft-thomson-postel-was-wrong
Stream Internet Architecture Board (IAB)
Expired & archived
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Stream IAB state (None)
Consensus boilerplate Unknown
RFC Editor Note (None)
This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at:


The robustness principle, often phrased as "be conservative in what you send, and liberal in what you accept", 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.


Martin Thomson

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)