Re: [Pce] Query regarding draft-ietf-pce-binding-label-sid-02

[Dhruv Dhody <[e-mail]>]

Hi Mrinmoy,

I will give authors some time to respond and confirm (and spin a new
update). I have noted this in the PCE WG wiki [
https://trac.ietf.org/trac/pce/wiki/WikiStart ] to make sure we could
track this to closure.

Thanks!
Dhruv

On Tue, Mar 24, 2020 at 7:11 PM Mrinmoy Das <[e-mail]> wrote:
>
> Hi Dhruv,
>
> Thanks for your quick reply.
>
> I have added PCE WG in this mail. More inline.
>
> Thanks & Regards,
> Mrinmoy
>
> On Tue, Mar 24, 2020 at 6:00 PM Dhruv Dhody <[e-mail]> wrote:
>>
>> Hi Mrinmoy,
>>
>> I was suggest you to also include [e-mail]; WG could benefit from
>> the discussion in future. More inline.
>>
>> On Tue, Mar 24, 2020 at 5:08 PM Mrinmoy Das <[e-mail]> wrote:
>> >
>> > Respected Authors and Contributors,
>> >
>> > Hope you all are doing well and safe in this tough times of Corona Virus Outbreak.
>> >
>> > I like to draw your attention regarding some parts of draft-ietf-pce-binding-label-sid-02 which I didn't able to understand properly.
>> >
>> > 1. BT = 0: The binding value is an MPLS label carried in the format
>> >
>> >   specified in [RFC5462] where only the label value is valid, and
>> >   other fields (TC, S, and TTL) fields MUST be considered invalid.
>> >   The Length MUST be set to 7.
>> >
>> >
>> >     Previous versions of private draft uses 4 byte to store MPLS 20 Bit label and ignores TC, S & TTL fields.
>>
>> The length in the previous version was 6, which was incorrect. The TLV
>> length is as per https://tools.ietf.org/html/rfc5440#section-7.1
>> Which didnt make sense and your calculation below is correct!
>>
>> >     But in IETF draft after TLV structure redefinition, total length of the TLV becomes 7, i.e. BT(1 Byte)+Reserved(3 Byte)+MPLS 20bit Label(3 Byte) = 7 Byte
>>
>> Yes
>>
>> >     So, now MPLS 20 Bit Labelwill be stored in 3 byte. Is it correct?
>>
>> You can consider it a case of rounding up 20 bits to 3 bytes.
>>
>>
>> >     If this is correct then I feel the wording of the above paragraph needs to be more specific, meaning in 3 Byte Label there will be no space for TTL, so
>> >     my suggestion is to make below correction:
>> >
>> >     BT = 0: The binding value is an MPLS label carried in the format
>> >
>> >   specified in [RFC5462] where only the label value is valid, and
>> >   other fields (TC, S, and TTL) fields MUST be considered invalid.
>> >   The Length MUST be set to 7.
>> >
>>
>> My suggestion would be not mention any of the other fields and talk
>> only of 20 bits of Label. I see other SR RFCs take similar approach.
>
>
> Sounds Good. I'm agree with you.
>
>>
>> >
>> > 2. In some cases, a stateful PCE can request the PCC to allocate a
>> >
>> >   binding value.  It may do so by sending a PCUpd message containing an
>> >   empty TE-PATH-BINDING TLV, i.e., no binding value is specified
>> >   (making the length field of the TLV as 2).  A PCE can also make the
>> >   request PCC to allocate a binding at the time of initiation by
>> >   sending a PCInitiate message with an empty TE-PATH-BINDING TLV.
>> >
>> >
>> >   As per new Binding TLV Structure below, BT is of 1 Byte and there will be 3 Byte Reserved.
>> >
>> >          0                   1                   2                   3
>> >
>> >        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>> >       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>> >       |             Type              |             Length            |
>> >       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>> >       |      BT       |                 Reserved                      |
>> >       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>> >       ~            Binding Value (variable length)                    ~
>> >       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>> >
>> >
>> >    Now, an empty Binding TLV should have length of BT(1 Byte) + Reserved (3 Byte) = 4 Byte instead of 2 Byte.
>> >
>> >    So, I do not understand how in the draft it is calculated as 2 Byte. Could you please give me some clue?
>>
>>
>> This seems to be an error IMHO. 4 seems to be correct.
>
>
> Okay. So what would  be your suggestion to developer who is implementing this draft? Should it be taken as 4? If draft needs correction
> when will that be published?
>>
>>
>> Thanks!
>> Dhruv
>>
>> >
>> > Thanks & Regards,
>> > Mrinmoy