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draft-klensin-rfc2821bis-10: ABNF discuss

2008-06-30 03:20:20

Dear SMTP interested people,

As some may have seen I held a discuss in two parts. The second part was unfortunately not discussed until last week at all with me. I would like to get your input into this question.

My discuss was started due to there was a rule which wasn't a rule, i.e. it didn't contain any elements. A clear syntax violation in ABNF. The rule in the issue was "Standardized-tag", this can be seen in version 10 of the draft in section 4.1.3.

I have received a proposal from John Klensin that would make section 4.1.3 read as below. The change is in the rule for General-address-literal and removal of Standardized-tag as a defined rule.

   General-address-literal  = <Standardized-tag> ":" 1*dcontent
        ; Standardized-tag MUST be specified in a
        ; standards-track RFC and registered with IANA

However, my personal objection against this resolution of the error is that it leaves use with a undefined rule that is intended for future extensions. I see this as a interoperability issue as any parser implemented according to the rules in this document will have the potential to fail on any future tag. If one could clarify what possible syntax that the future tags could have then this would not be an issue. I fully understand that the old implementation will still not understand the content, however, by not having the parsing fail an implementation can at least take the correct action. Thus I wonder why one can't specify it like:

Standardized-tag = ehlo-keyword

Any rule that defines what combination of character are allowed in any future tag would be fine as a solution to this issue from my perspective.

Is there a any problem with defining a rule for what characters is allowed in future tag for identifying literal address formats that is large enough to motivate living with the interoperability issue?


Magnus Westerlund

IETF Transport Area Director & TSVWG Chair
Multimedia Technologies, Ericsson Research EAB/TVM
Ericsson AB                | Phone +46 8 4048287
Färögatan 6                | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: 

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