Re: [bess] John Scudder's No Objection on draft-ietf-bess-evpn-oam-req-frmwk-08: (with COMMENT)

[Donald Eastlake <[e-mail]>]

Hi John,

On Wed, Apr 7, 2021 at 10:02 PM John Scudder <[e-mail]> wrote:
> Hi Donald,
>
> Thanks for your reply.
>
> On Apr 7, 2021, at 9:22 PM, Donald Eastlake <[e-mail]> wrote:
>
> ...
>
> 2. Section 2.3:
>
>    EVPN Network OAM mechanisms MUST provide in-band monitoring
>    capabilities. As such, OAM messages MUST be encoded so that they
>    exhibit identical entropy characteristics to data traffic in order
>    that they share the same fate.
>
> It’s not obvious to me what you mean by “identical entropy
characteristics to
> data traffic”. Surely, different flows may have different entropy
> characteristics, so, *which* data traffic? Similarly, with which data
traffic
> are you saying the OAM messages must share fate?
>
>
><de> Well, it depends on what is meant by "characteristics". I believe the
><de>intent is to say that with a sufficient quantity of OAM messages, all
><de>paths used by actual data will be exercised.
>
>
> Your explanation (“all paths… will be exercised”) seems inconsistent with
§3.1.1.1:
>
>    - all paths. For MPLS/IP networks with ECMP, monitoring of all
>      unicast paths between MEPs (on non-adjacent nodes) may not be
>      possible, since the per-hop ECMP hashing behavior may yield
>      situations where it is impossible for a MEP to pick flow entropy
>      characteristics that result in exercising the exhaustive set of
>      ECMP paths. Monitoring of all ECMP paths between MEPs (on non-
>      adjacent nodes) is not a requirement for EVPN OAM.
>
> Even if the above somehow isn't the issue it appears to be, I think it’s
evident that the §2.3 text in question isn’t unambiguous enough to have a
MUST applied to it, I think this needs to be rectified in some way. I’m
going to switch my ballot to a DISCUSS until we’ve resolved this.
>
> (Now that I’m looking at the §2.3 text again, “identical” bugs me too,
since identity is a much stronger requirement than, say, similarity. But
since I suspect the text will be rewritten anyway it’s not worth dwelling
on.)

<de>Geez, here I put this text, which I inherited when I became pen holder
after draft-salam-l2vpn-evpn-oam-req-frmwk, in the best possible light and
you still object !  :-)

<de> OK, how about something more like:

EVPN Network OAM mechanisms MUST provide in-band monitoring capabilities.
OAM messages SHOULD be encoded so that they exhibit similar entropy
characteristics to data traffic in order maximize the fate sharing between
OAM and data.


<de> Thanks,
Donald
=============================
 Donald E. Eastlake 3rd   [phone] (cell)
 2386 Panoramic Circle, Apopka, FL 32703 USA
 [e-mail]

> Thanks,
>
> —John