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

[Mrinmoy Das <[e-mail]>]

Thanks a lot Dhruv for the clarification.

Thanks & Regards,
Mrinmoy

On Wed, Apr 22, 2020 at 9:59 AM Dhruv Dhody <[e-mail]> wrote:

> Hi Mrinmoy,
>
> On Wed, Apr 22, 2020 at 9:35 AM Mrinmoy Das <[e-mail]>
> wrote:
> >
> > Hi All,
> >
> > If we only mention 20-bit label then what will be the structure of it?
> > As per generic MPLS label structure 24-bit used to look like as follows:
> >
> > |<--------20-bit---------->|<-3-bit->|<-1-bit->|
> > |<-MPLS 20-bit label->|<- TC ->|<-  S  ->|
> >
> > Now if we just mention about MPLS 20-bit label, is that mean following
> representation:
> >
> > |<-4-bit->|<--------20-bit---------->|
> > |<-all 0->|<-MPLS 20-bit label->|
> >
>
> No!
> The format is still based on RFC 5462 and thus it would look something
> like this -
>
>        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=7          |
>       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>       |      BT=0     |                 Reserved                      |
>       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>       |                Label                  | all zeros (ignore)    |
>       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
> Even though the length=7, you will need to process the Binding Value
> field based on the Binding Type (BT) which says that the format is as
> per RFC 5462.
>
> Note that the extra byte of zeros at the end is for padding as per
> https://tools.ietf.org/html/rfc5440#section-7.1 and not counted in the
> length.
>
> Stay Safe!
> Dhruv
>
> PS. Request the authors to update the draft SOON based on Mrinmoy's
> original email.
>
> > Thanks & Regards,
> > Mrinmoy
> >
> > On Wed, Mar 25, 2020 at 3:56 PM stefano previdi <[e-mail]>
> wrote:
> >>
> >> 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
> >>
>