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

["BRUNGARD, DEBORAH A" <[e-mail]>]

I agree with Stewart - for the two bits to be set would be an implementation error. Not an operational error. The use of the two bits has been stable from the -00 version of the draft. There are always multiple ways to do a protocol design. And various tradeoffs. There are also operational positives for having two bits. Sub-TLVs are very common (PW, MPLS, GMPLS). The extra bit in an optional sub-TLV used when setting up a path is not going to break any bandwidth bank:-)

As Stewart noted on his other email, PALS followed the Routing Area process of asking on IPR at the time of Last Call. We don't require positive confirmation that no one has concerns, only if they have concerns.

Much thanks Mirja for your interest and very comprehensive review - let us know if Stewart's proposal is acceptable to clear your discuss.

Deborah

-----Original Message-----
From: iesg [mailto:[e-mail]] On Behalf Of Stewart Bryant
Sent: Wednesday, July 06, 2016 8:58 AM
To: Mirja Kuehlewind <[e-mail]>; The IESG <[e-mail]>
Cc: [e-mail]; [e-mail]; [e-mail]
Subject: Re: Mirja Kühlewind's Discuss on draft-ietf-pals-mpls-tp-pw-over-bidir-lsp-08: (with DISCUSS and COMMENT)



>>
>> ----------------------------------------------------------------------
>> 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