Re: [Pals] Mirja Kühlewind's Discuss on draft-ietf-pals-mpls-tp-pw-over-bidir-lsp-08: (with DISCUSS and COMMENT)

[Stewart Bryant <[e-mail]>]

>>
>> ----------------------------------------------------------------------
>> DISCUSS:
>> ----------------------------------------------------------------------
>>
>> I think the protocol specification is not complete:
>>
>> - What happens if none of the two S and C bits are set?
> Since the text specifically states that they are mutually exclusive, 
> that would be
> an implementation error. I don't think that it is within the scope of 
> this draft to
> state what should happen when there is an implementation error.

Thinking about this some more, we could say:

    Either the C-bit or the S-bit MUST be set.
    the C-bit and S-bit are mutually exclusive from each other, and 
cannot be
    set in the same message.  Otherwise, a Label Release message with
    status code set to "The C-bit and S-bit can not both be set" (TBD5)
    MUST be replied, and the PW will not be established.

We could introduce an additional error message, but it's probably 
adequate to
say:

    Either the C-bit or the S-bit MUST be set.
    The C-bit and S-bit are mutually exclusive from each other, and 
cannot be
    set in the same message.  In the case of either error, a Label 
Release message with
    status code set to "The C-bit and S-bit error" (TBD5)
    MUST be replied, and the PW will not be established.

If parametrised messages are allowed I would say:

"The C-bit and S-bit error [<C-bit>, <S-bit>]"

Since zero or two bits are clearly an implementation error, I am not
convinced that we need to do more than flag it up sufficiently that
the an implementer can figure out what they got wrong.

Stewart