Florian Weimer wrote: > * W. C. A. Wijngaards: > >> > +1. Backwards compatibility means you cannot specify that existing >> > implementations have to change. > > Does it matter if they do not exist or are not considered practically > relevant?
not usually. if there's a standard for it, our burden is to assume that there are faithful implementations of it. only if there is no way to negotiate for the new behaviour (as there would be for tcp stay-open, so this exception does not apply to the draft under consideration) would we even consider assuming otherwise. > As a counterexample, RFC 6891 requires FORMERR responses without OPT > RRs from implementations which do not support EDNS: > > Responders that choose not to implement the protocol extensions > defined in this document MUST respond with a return code (RCODE) of > FORMERR to messages containing an OPT record in the additional > section and MUST NOT include an OPT record in the response. this language was very careful. older implementations cannot "choose" behaviour relative to this standard. so, as an example of what you're trying to convey, this text fails. -- Paul Vixie
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