Re: [sfc] WGLC for https://datatracker.ietf.org/doc/draft-ietf-sfc-ioam-nsh/

[Greg Mirsky <[e-mail]>]

Dear WG Chairs, Authors, and the WG community,
two weeks ago I've shared my thoughts, concerns related to
draft-ietf-sfc-ioam-nsh. So far, I haven't seen any comments from the WG,
nor responses from the Authors. It could be that my note got buried under
other emails. I want to recapitulate my position - the scope of the draft
seems more narrow than what was already produced by the IPPM WG (the WG LC
on two IOAM drafts has concluded). Considering the level of maturity of
IOAM specifications from the IPPM WG, it seems beneficial to have a single
document describing for the SFC NSH the applicability of all defined up to
date IOAM tracing options.
I hope that the Authors and the WG community will share their opinions.
Below is a copy of my earlier comments.

Regards,
Greg

On Tue, Sep 7, 2021 at 3:00 PM Greg Mirsky <[e-mail]> wrote:

> Dear Authors and All,
> I've read the current version of the draft and have some comments I'd like
> to share with you. I much appreciate your thoughts on where this work
> should go considering developments in other IETF WGs. Please find my notes
> and questions below:
>
>    - It is stated in the Abstract that:
>
>    In-situ Operations, Administration, and Maintenance (IOAM) records
>    operational and telemetry information in the packet while the packet
>    traverses a path between two points in the network.
>
> But that is the case only for the pre-allocated and incremental trace
> option types. The Direct Export option
> <https://datatracker.ietf.org/doc/draft-ietf-ippm-ioam-direct-export/>
> does not write telemetry data into the data packet itself but export
> telemetry information in a specially constructed packet.
> And as we are talking about different IOAM trace options, the question of
> the scope of this document seems appropriate. There is a WGLC on two IOAM
> documents
> <https://mailarchive.ietf.org/arch/msg/ippm/A0OcGQ5LlNjnjfRVp_iUTMYMrcs/>
> active through September 15th at the IPPM WG. I believe that it would be
> beneficial if we had a single document that describes the applicability of
> IOAM in all its functionality defined by documents in IPPM WG. Of course,
> that cannot be a moving target as that would not be helpful. But since the
> IPPM WG discusses the progress of two IOAM documents, it could be a great
> time to address the applicability of the Direct Export trace type
> <https://datatracker.ietf.org/doc/draft-ietf-ippm-ioam-direct-export/>
> and Loopback and Active flags defined in draft-ietf-ippm-ioam-flags
> <https://datatracker.ietf.org/doc/draft-ietf-ippm-ioam-flags/>. It would
> be concerning to have more than one SFC document describing the
> applicability of the generic IOAM mechanisms.
>
>
>    - The location of the IOAM header in the SFC NSH-encapsulated packet
>    is defined in Section 3:
>
>    IOAM-Data-Fields are carried in NSH
>    using a next protocol header which follows the NSH MD context
>    headers.
>
> I've checked RFC 8300 but couldn't find it defines the Next Protocol
> header. Also, it appears that NSH Context headers are optional. Hence my
> question. Is the presence of an NSH Context header required when using
> IOAM? Could you clarify which mechanism is used to identify the payload of
> an SFC NSH-encapsulated packet as IOAM?
>
>
>    - If I understand the format of the IOAM header defined in Section 3
>    correctly, the header's length is limited by 1020 octets, while the
>    effective length containing IOAM options and data - 1016 octets. Is that
>    correct? What is the recommended technique of collecting IOAM data that
>    exceeds that limit?
>    - In Section 4.1, I've found the text reflecting the history of the
>    discussion about how to carry the IOAM header using NSH encapsulation. As
>    the text has no normative value, I suggest moving it into an Appendix.
>    - I find the rules of handling the O-bit in NSH listed in Section 4.2
>    inconsistent and confusing. The IOAM header is not part of NSH
>    encapsulation but is a part of the payload. But in one case, when user data
>    follows it, the O-bit must not be set as. If there's no user data after the
>    IOAM header, then the O-bit must be set. But from the perspective of NSH
>    encapsulation, it includes specially constructed data added for the sole
>    purpose of collecting OAM/telemetry information. Then, why, in one case,
>    the O-bit is cleared and in the other set if, in both cases, the
>    NSH-encapsulated packet is used to perform the OAM function?
>
> I much appreciate your consideration of my comments and questions and
> looking forward to your feedback.
>
> Regards,
> Greg
>
> On Wed, Aug 18, 2021 at 5:32 AM James Guichard <
> [e-mail]> wrote:
>
>> Dear WG:
>>
>>
>>
>> This email starts a 2 week Working Group Last Call for
>> draft-ietf-sfc-ioam-nsh [1].
>>
>>
>>
>> Please read this document if you haven’t read the most recent version and
>> send your comments to the SFC WG list no later than September 1st 2021.
>>
>>
>>
>> If you are raising a point which you expect will be specifically debated
>> on the mailing list, consider using a specific email/thread for this point.
>>
>>
>>
>> Lastly, if you are an author or contributor please response to indicate
>> whether you know of any undisclosed IPR related to this document.
>>
>>
>>
>> Thanks!
>>
>>
>>
>> Jim & Joel
>>
>>
>>
>> [1] https://datatracker.ietf.org/doc/draft-ietf-sfc-ioam-nsh/
>>
>>
>>
>>
>>
>>
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>