Hi, all, ... > Title : The Harmful Consequences of > Postel's Maxim > https://tools.ietf.org/html/draft-thomson-postel-was-wrong-01 I completely agree with John Klensin that a test suite defines the protocol standard (warts and all). However, I disagree with the characterization of the Postel Principle in this doc, and strongly disagree with one of its key conclusions ("fail noisily in response to...undefined inputs"). Failing in response to bad inputs is fine, but "undefined" needs to be treated agnostically. IMO, the Postel Principle is an admission of that sort of agnosticism - if you don't know how the other end will react, act conservatively. If you don't know what the other end intends, react conservatively. Both are conservative actions - in one sense, you try not to trigger unexpected behavior (when you send), and in another you try not to create that unexpected behavior (when you receive). That's the very definition of how unused bits need to be handled. Send conservatively (use the known default value), but allow any value upon receipt. The principle does not setup the feedback cycle in Sec 2; a bug is a bug and should be fixed, and accommodating alternate behaviors is the very definition of "be generous in what you receive". "Being conservative in what you send" doesn't mean "never send anything new" - it means do so only deliberately. ----- Failing noisily is, even when appropriate (e.g., on a known incorrect input), an invitation for a DOS attack. That behavior is nearly as bad as interpreting unexpected (but not prohibited) behavior as an attack. Neither one serves a useful purpose other than overreaction, which provides increased leverage for a real DOS attack. Joe