Re: [spring] WGLC - draft-ietf-spring-srv6-network-programming

Greg Mirsky <gregimirsky@gmail.com> Sun, 12 January 2020 03:01 UTC

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From: Greg Mirsky <gregimirsky@gmail.com>
Date: Sat, 11 Jan 2020 23:01:01 -0400
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To: "Pablo Camarillo (pcamaril)" <pcamaril@cisco.com>
Cc: "spring@ietf.org" <spring@ietf.org>
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Subject: Re: [spring] WGLC - draft-ietf-spring-srv6-network-programming
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Hi Pablo,
thank you for your expedient response. Please find my new notes under GIM>>
tag below in-line.

Regards,
Greg

On Fri, Jan 10, 2020 at 1:09 PM Pablo Camarillo (pcamaril) <
pcamaril@cisco.com> wrote:

> Hi Greg,
>
>
>
> Inline.
>
>
>
> Thanks,
>
> Pablo.
>
>
>
> *From: *Greg Mirsky <gregimirsky@gmail.com>
> *Date: *Tuesday, 7 January 2020 at 21:01
> *To: *Bruno Decraene <bruno.decraene@orange.com>
> *Cc: *SPRING WG List <spring@ietf.org>rg>, "6man@ietf.org" <6man@ietf.org>rg>,
> draft-ietf-spring-srv6-network-programming <
> draft-ietf-spring-srv6-network-programming@ietf.org>
> *Subject: *Re: WGLC - draft-ietf-spring-srv6-network-programming
> *Resent from: *<alias-bounces@ietf.org>
> *Resent to: *<cf@cisco.com>om>, <pcamaril@cisco.com>om>, <john@leddy.net>et>, <
> daniel.voyer@bell.ca>gt;, <satoru.matsushima@g.softbank.co.jp>jp>, <
> lizhenbin@huawei.com>
> *Resent date: *Tuesday, 7 January 2020 at 21:01
>
>
>
> Dear Authors, WG Chairs, et al.,
>
> I hope I'm not too late with my comments and questions on the document. Please
> kindly consider them as WG LC comments:
>
> ·         I have a question regarding the following pseudo-code:
>
>   S08.   max_LE = (Hdr Ext Len / 2) - 1
>
>   S09.   If ((Last Entry > max_LE) or (Segments Left > (Last Entry+1)) {
>
>   S10.      Send an ICMP Parameter Problem to the Source Address,
>
>                Code 0 (Erroneous header field encountered),
>
>                Pointer set to the Segments Left field.
>
>                Interrupt packet processing and discard the packet.
>
>   S11.   }
>
>
>
> According to RFC 8200, Hdr Ext Len is the length of the extension header
> in 8-octet units, not including the first 8 octets. Thus, as I understand,
> max_LE is the length in 8-octet units of half of the extension header less
> one. On the other hand, Last Entry and Segments Left are indices. Hence my
> question, What is being compared in line S09 ( Last Entry > max_LE)? Length
> and index? If the goal is to use Hdr Ext Len to calculate the number of
> entries in the header, then what assumption is used in S08? Is it that the
> entry's length is always and only 128 bits, i.e. 16 octets? I believe that
> using such an assumption is too narrowing and limiting to SRH.
>
>
>
> PC: This has already been discussed with Adrian. Please check this thread:
> https://mailarchive.ietf.org/arch/msg/spring/IOA_4nlNPacD2v7Jue2dkGeOABk
>
> GIM>> Thank you for the reference. In some aspects, part of my statement
is repeating your answer to Adrain. The only length on an element in SRH
considered is 128 bits, the length of IPv6 address. I think that your
explanation of how you have arrived at th following formula

    S08.   max_LE = (Hdr Ext Len / 2) - 1

 will benefit the document.
My question to you and SPRING WG goes beyond this scenario. Considering
presented in Singapore Unified Identifier proposals (
draft-mirsky-6man-unified-id-sr
<https://datatracker.ietf.org/doc/draft-mirsky-6man-unified-id-sr/> and
draft-wmsaxw-6man-usid-id-use
<https://datatracker.ietf.org/doc/draft-gmsm-bess-evpn-bfd/?include_text=1>),
I believe other scenarios of using SRH, with elements of length other than
128 bits should be accommodated, e.g., 32 bits-long elements.

i.

>
>
> ·         Another question is to Section 6.3. What value do you see in
> this section? I've noticed that draft-ietf-6man-spring-srv6-oam is in the
> Informational References section. I agree with that for the first sentence
> in the section. But I believe that the second sentence that refers to the
> new O-bit and OAM behaviors defined in  draft-ietf-6man-spring-srv6-oam
> requires it to be moved into the Normative References section. Unless
> you'll decide to remove the section altogether.
>
> PC: The O-bit and OAM behaviors described in draft-ietf-6man-spring-srv6-oam
> are not required to understand or implement the technology described in
> draft-ietf-spring-srv6-network-programming. However, they are relevant as
> to provide additional information to the reader. Why would it be a
> normative reference?
>
GIM>> Ali and I are discussing several aspects of
draft-ietf-6man-spring-srv6-oam. For example, the O-bit is applicable to
any OAM operation or to some part of them. Note that OAM apparatus usually
considered to include Fault Management and Performance Monitoring
protocols. Both may operate as proactive or on-demand. Is the O-bit
applicable to all OAM methods? Then, Fault Management OAM supports
Continuity Check, Connectivity Verification and, for some networks,
Automatic Protection Coordination. How O-bit is used in these methods? Now,
to the Performance Monitoring OAM. I think that the O-bit can be only used
in dual-ended one-way PM OAM. How O-bit may be used in single-ended two-way
PM OAM? Can the O-bit support the Loss Measurement? As you may see, there
are many questions to discuss and clarify in the document. I can imagine
that the result of our work on draft-ietf-6man-spring-srv6-oam may be
somewhat different from its current form. How to ensure synchronization
between SRv6 programming and OAM specifications?

>
>
> Regards,
>
> Greg
>
>
>
> On Thu, Dec 5, 2019 at 9:15 AM <bruno.decraene@orange.com> wrote:
>
> Hello SPRING,
>
>
>
> This email starts a two weeks Working Group Last Call on draft-ietf-spring-srv6-network-programming [1].
>
>
>
> Please read this document if you haven't read the most recent version, and send your comments to the SPRING WG list, no later than December 20.
>
>
>
> You may copy the 6MAN WG for IPv6 related comment, but consider not duplicating emails on the 6MAN mailing list for the comments which are only spring specifics.
>
>
>
> 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.
>
> This may help avoiding that the thread become specific to this point and that other points get forgotten (or that the thread get converted into parallel independent discussions)
>
>
>
> Thank you,
>
> Bruno
>
>
>
> [1] https://tools.ietf.org/html/draft-ietf-spring-srv6-network-programming-05
>
>
>
>
>
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