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

[stefano previdi <[e-mail]>]

Hi Dhruv, 

I agree with your proposed changes:

1. only mention the 20 bits label value
2. fix the length to 4.


Thanks.
s.


> On Mar 24, 2020, at 3:14 PM, Dhruv Dhody <[e-mail]> wrote:
> 
> 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