[mpls] Re: WG last call: draft-ietf-mpls-inband-pm-encapsulation

Hi Xiao Min,
thank you for your expedient response. Please find my notes below tagged
GIM>>.

Regards,
Greg

On Sun, May 5, 2024 at 7:30 PM <xiao.min2@zte.com.cn> wrote:

> Hi Greg,
>
>
> Thanks for your review and comments.
>
> Please see inline.
> Original
> *From: *GregMirsky <gregimirsky@gmail.com>
> *To: *Tony Li <tony.li@tony.li>;
> *Cc: *mpls <mpls@ietf.org>;mpls-chairs <mpls-chairs@ietf.org>;
> *Date: *2024年05月04日 03:38
> *Subject: **Re: [mpls] WG last call:
> draft-ietf-mpls-inband-pm-encapsulation*
> _______________________________________________
> mpls mailing list
> mpls@ietf.org
> https://www.ietf.org/mailman/listinfo/mpls
>
> Hi, Tony and All,
> I've read the latest version of the draft. Please find my comments below:
>
>    -
>
>    The proposed mechanism, as stated in Abstract, applies to "MPLS live
>    traffic". I couldn't find the definition of the term "live traffic" and
>    appreciate it if you can clarify it for me. Does that apply to any MPLS
>    packet or a particular class of MPLS packets in a network?
>
>    [XM]>>> That applies to a flow of MPLS packets in a network. In the
>    Abstract of RFC 9341 it says "This document describes the
>    Alternate-Marking technique to perform packet loss, delay, and jitter
>    measurements on live traffic".
>
> GIM>> Thank you for the reference to RFC 9341. Although I am one of th
co-authors of that RFC, thinking of it now, I find the characterization
"live traffic" ambigious. Is there in the network traffic other than
"live"? I cannot find an example of such case. If you agree, perhaps
finding a more technical term or removing "live" altogether is possible.

>
>    -
>
>    I appreciate that the document mentions work on Synonymous Flow
>    Labels. However, it is not clear to me why SFL-based application of the AMM
>    is characterized as hop-by-hop, while the solution described in the draft -
>    as edge-to-edge. I would appreciate it if the authors can clarify that
>    characterization of measurement methods, particularly since the T-bit
>    (defined in Figure 1) differentiates between edge-to-edge and hop-by-hop
>    measurements using the proposed solution.
>
>    [XM]>>> Note that the text means the SFL method mainly aims at
>    edge-to-edge processing, not hop-by-hop. And you're right that the method
>    described in this document can be used for both hop-by-hop and
>    edge-to-edge, although the main application scenario is hop-by-hop.
>
> GIM>> How "the SFL method mainly aims" is determined? Is that stated in
any of SFL documents? At the same time, if the proposed mechanism is aimed
for the particular use case, extending it to support anything else adds, in
my opinion, is an unecessary complexity. If, as you've stated, supporting
the Alternate Marking method in the MPLS network is not intended with
edge-to-edge scope, then it seems that the T-bit is not needed and can be
changed to R(eserved). Even more reason to do that, in my view, is that the
scope of the PM supported by the Alternate Marking method (and on-path
telemetry in general) can be easily controled via the management plane by
controling the appropriate configuration parameters.

>
>    -
>
>    Furthermore, it seems like the comparison of the impact on an MPLS
>    packet of the proposed solution and IOAM is inaccurate. As I understand it,
>    contrary to the statement in Introduction that "the former doesn't
>    introduce any new header whereas the latter introduces a new In-situ OAM
>    header", both introduce (unlike SFL-based application of AMM) extra
>    ancillary data in an MPLS packet.
>
>    [XM]>>> Can the ISD be seen as a new header? I personally don't think
>    so. If you have any text change proposal, it's much appreciated. :-)
>
> GIM>> Sorry, but I don't understand your question. IOAM can be supported
by ISD MNA (draft-mb-mpls-ioam-dex
<https://datatracker.ietf.org/doc/draft-mb-mpls-ioam-dex/>), and AFAICS,
the impact of supporting IOAM-DEX using ISD MNA is comparable with the
solution proposed in this document or draft-cx-mpls-mna-inband-pm
<https://datatracker.ietf.org/doc/draft-cx-mpls-mna-inband-pm/>. I would
consider removing this subjuective comparison altogether from the document.

>
>    -
>
>    And, on the last paragraph in Introduction. I believe that publishing
>    a draft on Standard track and then moving it to Historic once another
>    solution is standardized by IETF is sub-optimal. I recognize the value of
>    the work put in by implementers of the described in the draft solution. The
>    deployment experience is invaluable. On the other hand, there seems to be
>    an agreement that the MNA is the preferred mechanism to support AMM in the
>    MPLS networks. (Note that draft-ietf-mpls-mna-usecases is being updated to
>    include AMM as another use cases of on-path telemetry in the MPLS networks,
>    in addition of IOAM). Hence my proposal to switch this document to
>    Experimental track (see my question about the requested IANA allocation
>    below).
>
>    [XM]>>> I agree with Tony and Loa on this point. To be clear, it's
>    preferred to publish this document as a Standards Track RFC.
>
>
>    -
>
>    The list of implementations is impressive and suggests that there are
>    several deployments. If that is the case, which value of eSPL for Flow-ID
>    Label Indicator is used?
>
>    [XM]>>> It's my fault not requesting an early allocation. Anyway, I
>    believe allocating a permanent code point for this feature is optimal for
>    the existing and potential implementers and deployers.
>
> GIM>> Perhaps you can help understanding the state of the existing
implementations that, as I look at the issue, is confusing. On one hand,
some of implementations have demonstrated their interoperability. And, one
can assume, that that is achieved using a value from the Unassigned range
of Extended Special-Purpose MPLS Label Values
<https://www.iana.org/assignments/mpls-label-values/mpls-label-values.xhtml#extended>.
On the other hand, a new value is requested and there's non-zero
propbability that the assigned value would not be the one already used in
the existing implementations. If implemeters squatted (using Tony's term)
on the IANA registry, would it be better to identify that value and request
it to be assigned to the solution described in this document?

>
> Best Regards,
>
> Xiao Min
>
>
> In conclusion, I don't support progressing this draft on the Standard
> track. I would support progressing it as Experimental or Informational
> (perhaps that means that the IANA section is removed).
>
> Regards,
> Greg
>
> On Thu, Apr 25, 2024 at 8:09 AM Tony Li <tony.li@tony.li> wrote:
>
>>
>> [WG chair hat: on]
>>
>>
>> Hi all,
>>
>> This starts a 2 week working group last call on
>> draft-ietf-mpls-inband-pm-encapsulation.
>>
>> This last call ends at 12:01 PM PDT, Thurs. May 9, 2024.
>>
>> Please send all comments to the mailing list.
>>
>> Regards,
>> Tony
>>
>>
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>>
>
>