Re: RFC 2119 section 6

[Alan Barrett <[e-mail]>]

On Wed, 4 Jul 2001, D. J. Bernstein wrote:
> Why are you trying to weasel out of this? Why are you trying
> to force me to change djbdns in ways that aren't required for
> interoperability?

I would say that ignoring non-answer fields in AXFR, as described in
axfr-clarify, is required for interoperability with potential future
extensions to the protocol.

Thinking about extensibility is an important part of protocol
design.  IETF protocols include many examples of such forethought,
often in the form of fields reserved for future use with language
like "MUST be zero when transmitted, MUST be ignored when received".
Interoperability with future extensions is harmed when the sender
fails to zero such fields, and is also harmed when the receiver
fails to ignore such fields.

It's perfectly appropriate to use "MUST" or "MUST NOT" when
specifying behaviour that is expected to enable or interfere with
future extensibility.

--apb (Alan Barrett)



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