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

From: John Scudder via Datatracker <[email-masked]>
Date: Wed, 07 Apr 2021 14:53:54 -0700

John Scudder has entered the following ballot position for
draft-ietf-bess-evpn-oam-req-frmwk-08: No Objection

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COMMENT:
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Thanks for the clear and readable document. I have one nit and one question.

1. Section 1, nit:

“EVPN is an Layer 2” s/an/a/

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?

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From: Donald Eastlake <[email-masked]>
Date: Wed, 7 Apr 2021 21:22:50 -0400

Hi John,

Thanks for the comments, see below.

On Wed, Apr 7, 2021 at 5:53 PM John Scudder via Datatracker
<[email-masked]> wrote:
> ...

OK.

> are you saying the OAM messages must share fate?

Well, it depends on what is meant by "characteristics". I believe the
intent is to say that with a sufficient quantity of OAM messages, all
paths used by actual data will be exercised.

Thanks,
Donald
===============================
 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
 2386 Panoramic Circle, Apopka, FL 32703 USA
 [email-masked]

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From: John Scudder <[email-masked]>
Date: Thu, 8 Apr 2021 02:02:46 +0000

Hi Donald,

Thanks for your reply.

On Apr 7, 2021, at 9:22 PM, Donald Eastlake <[email-masked]<mailto:[email-masked]>> wrote:
...
2. Section 2.3:

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.)

Thanks,

—John

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From: Donald Eastlake <[email-masked]>
Date: Thu, 8 Apr 2021 00:12:39 -0400

Hi John,

On Wed, Apr 7, 2021 at 10:02 PM John Scudder <[email-masked]> wrote:
> Hi Donald,
>
> Thanks for your reply.
>
> On Apr 7, 2021, at 9:22 PM, Donald Eastlake <[email-masked]> wrote:
>
> ...
>
> 2. Section 2.3:
>
><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.
>
>
> 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   +1-508-333-2270 (cell)
 2386 Panoramic Circle, Apopka, FL 32703 USA
 [email-masked]