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RE: DRAFT Montreal minutes - X#NodeArchitecture comments

>>>>> "Mallikarjun" == Mallikarjun C <cb_mallikarjun@xxxxxxxxx> writes:

 Mallikarjun> Hi Ken, Can you please point me to RFC 3720 text that
 Mallikarjun> says NotUnderstood is always an error?

 Mallikarjun> The closest I can find is in section 5.2, page 55:

Page 54, second paragraph:

   The constants "None", "Reject", "Irrelevant", and "NotUnderstood" are
   reserved and MUST ONLY be used as described here.  Violation of this
   rule is a protocol error (in particular the use of "Reject",
   "Irrelevant", and "NotUnderstood" as proposed values).

"as described here" is as responses to negotiating keys.  The text
already explicitly disallows their use as proposals.  

A declaration isn't exactly the same as a proposal, but it certainly
isn't a reply to a proposal, so by the above text "NotUnderstood" is

The 3720 bug is this: an implementation that doesn't understand a key
doesn't know whether that key is declarative or negotiated.  If it
assumes the latter it would have to reply NotUnderstood.  If in fact
it was a declarative key then by the current text that's a protocol

A good way to fix this is to add two rules:

1. If a key is not understood, it is assumed to be a negotiation
   key (and a NotUnderstood reply must be sent).
2. If a declarative key is sent, and a reply is received from the
   other end with that key and a value of NotUnderstood, this is
   a protocol violation only if the key is required to be implemented.
   If it was not required (i.e., X# keys) then a NotUnderstood
   reply must be silently ignored.


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