Hi Yubao, Sorry for the delay in response and thanks for catching this issue. We'll try to correct this during the AUTH48 process.
Please check inline below. On Thu, May 26, 2022 at 8:20 AM <wang.yub...@zte.com.cn> wrote: > > Hi authors, > > > There may be conflicting description in > draft-ietf-bess-srv6-services-15#section-6.1.1 > <https://datatracker.ietf.org/doc/html/draft-ietf-bess-srv6-services-15#section-6.1.1> > on the usage of Transposition Length. > > > <draft-ietf-bess-srv6-services-15#section-6.1.1> > > The 24-bit ESI label field of the ESI label extended community > > carries the whole or a portion of the Argument part of the SRv6 SID > > when the ESI filtering approach is used along with the Transposition > > Scheme of encoding (Section 4) and otherwise set to Implicit NULL > > value. *In either case*, *the value* is set in *the high order 20 > bits* > > (e.g., as 0x000030 in the case of Implicit NULL). When using the > > Transposition Scheme, the *Transposition Length* MUST be less than or > > *equal to 24* and less than or equal to the Argument Length. > > </draft-ietf-bess-srv6-services-15> > > > I think that "The value" which is set in "the high order 20 bits" should > be the same thing as "the whole or a portion of the Argument part of the > SRv6 SID", > > If this is true, the length of "The value" (which is also the > Transposition Length) can only be as much as 20, it can't be equal to 24. > > Otherwise, "The value" may have to be carried in the high X bits of the > ESI label field (wherein X is the argument length), not always the "the > high order 20 bits". > > > KT> This is an error in the draft. Since the field is 24-bit, we should just say "set in the 24 bits" instead of the existing text "set in the high order 20 bits". This applies to all EVPN encodings in the draft. > I also noted that in some other sections(e.g. Section 5.1), it is clearly > described that the Transposition Length MUST be no more 20. > KT> This depends on the encoding for the specific AFI/SAFI. For those that use the RFC8277 label encoding, the transposition length is limited to 20. That is why the "high order" clarification came in but it does not apply to EVPN. Please also see the following text in Sec 3.2.1 The size of the MPLS label field limits the bits transposed from the SRv6 SID value into it. E.g., the size of MPLS label field in [RFC4364 <https://datatracker.ietf.org/doc/html/rfc4364>] [RFC8277 <https://datatracker.ietf.org/doc/html/rfc8277>] is 20 bits while in [RFC7432 <https://datatracker.ietf.org/doc/html/rfc7432>] is 24 bits. > So I think may be the transposition length for EVPN routes is not > necessary to be greater than 20. > KT> For EVPN encodings the field is 24-bit and so we can transpose up to 24 bits. > If it is greater than 20, the TC/S field of the ESI label may have to be > used, > KT> There is no TC/S encoding in the ESI label field. > and the bit order may be not the same "In either case". > KT> I am not sure what you mean by bit order. If you are referring to byte ordering then everything is in network byte order. Thanks, Ketan > Because that if the Transposition Length is less than 21, it MUST be > cairried in the high order 20 bits (along with some padding bits) according > to the history of this draft, not just the high X bits. > > Is my understanding correct? > > > Glad to receive any clarifications. > > > Thanks, > > Yubao > > > > >
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