Re: [Idr] draft-rekhter-rfc4760bis-01

[John Scudder <[e-mail]>]

On Oct 11, 2010, at 7:36 AM, Jie Dong wrote:
> Besides, I note that the description about the reserved field in Capability
> Advertisement (Section 8) is unchanged:
> 
>        " Res. - Reserved (8 bit) field. SHOULD be set to 0 by the sender
>         and ignored by the receiver.
> 
>         Note that not setting the field value to 0 may create issues
>         for a receiver not ignoring the field. In addition this
>         definition is problematic if it is ever attempted to redefine
>         the field."
> 
> I'm not sure if there is some implementation which can cause issues with
> this field not setting to zero. But this description makes it impossible to
> redefine this field. If there is no such inappropriate implementation, I
> would recommend not to forbid the redefining of this field.

Seems to me as though this can be addressed by changing the SHOULD to a MUST: "MUST be set to 0 by the sender and MUST be ignored by the receiver."  As far as I'm concerned the "note that" paragraph is entirely optional.  In any case it's informative, not normative.  For that matter I don't think "this definition is problematic if it is ever attempted to redefine the field", it seems to have the same characteristics as any other set of flags.  Since the paragraph seems to be confusing, maybe it should just be removed.

As usual, the way you would introduce new flags to the field is by revising the spec.  The "MUST be ignored" is what makes this (reasonably) safe.

--John