Re: [mpls] [spring] should draft-ietf-mpls-spring-entropy-label be published as a RFC on the standards track?

Stewart,

                At least one view of the purpose of an Entropy label is that it _adds_ entropy to the process of path selection.

                Explicitly limiting EL behavior to rely exclusively on use of the entropy label would also explicitly _limit_ the total entropy to whatever the implementation that provided the entropy label was implemented to treat as _sufficient_ among all paths in the ECMP gestalt, possibly including branches that implementation might not know about.

                I doubt very much that many of the problems you refer to would have arisen if folks generally felt that the entropy label – by itself – provides sufficient entropy.

                It might make sense to impose this restriction – optionally – when a deployment occurs in which any particular pathological behavior might be expected to occur.

                In that case, it might be very important to ensure that the limited approaches available for maximizing efficient load distribution via explicit and exclusive use of the entropy label are acceptable to a reasonably diverse set of implementers, as support for at least one of those approaches would then become a mandatory part of every standard implementation.

                Even so, I don’t believe it is a good idea to restrict implementations from using other approaches in every case.

                The simplest example possible (where doing so is a big problem) is one where the entropy labels provided have N possible values  and there are M possible paths, where M>N. In any scenario where this occurs, M-N paths simply will not be used.

--
Eric

From: mpls [mailto:mpls-bounces@ietf.org] On Behalf Of Stewart Bryant
Sent: Wednesday, May 02, 2018 9:52 AM
To: Andrew G. Malis <agmalis@gmail.com>; Loa Andersson <loa@pi.nu>
Cc: mpls@ietf.org; spring@ietf.org; mpls-ads@ietf.org; draft-ietf-mpls-spring-entropy-label@ietf.org
Subject: Re: [mpls] [spring] should draft-ietf-mpls-spring-entropy-label be published as a RFC on the standards track?

Be careful.

There is text in the draft that talks about ECMP behaviour in different parts of the path, which implies an expectation that the EL is the sole source of entropy. If we make this ST then we will be implicitly standardizing that behaviour. Now as it happens, I thing we need to update the EL behaviour to make it the sole source of entropy, because that solves a number of problems, particularly in network instrumentation, but we need to do that explicitly and not as an artefact of this draft.

So the way I see it, either this draft is published as informational, or it is published as ST without any text that implies that the EL is the sole source of entropy, or we harden the EL behaviour (which I think we need to do) and this draft is published with a normative reference to an RFC that specifies the stricter EL behaviour.

- Stewart

On 02/05/2018 14:01, Andrew G. Malis wrote:
Loa,

There’s plenty of RFC 2119 language in the draft, so I support making this standards track.

Cheers,
Andy

On Wed, May 2, 2018 at 3:44 AM, Loa Andersson <loa@pi.nu<mailto:loa@pi.nu>> wrote:
Working Group,

February 1st the MPLS working Group requested that draft-ietf-mpls-
spring-entropy-label should be published as an Informational RFC.

During the RTG Directorate and AD reviews the question whether the
document should instead be published as a RFC on the Standards Track
has been raised.

The decision to make the document Informational was taken "a long time
ago", based on discussions between the authors and involving the
document shepherd, on the wg mailing list. At that point it we were
convinced that the document should be progressed as an Informational
document.

It turns out that there has been such changes to the document that we
now would like to request input from the working group if we should make
the document a Standards Track RFC.

Daniele's RTG Directorate review can be found at at:
https://datatracker.ietf.org/doc/review-ietf-mpls-spring-entropy-label-08-rtgdir-lc-ceccarelli-2018-02-21/

All the issues, with the exception whether it should be Informational
or Standards track, has been resolved as part AD review.

If the document is progressed as a Standard Tracks document then we
also need to answer the question whether this is an update RFC 6790.

This mail starts a one week poll (ending May 9) to see if we have
support to make the document a Standards Track document. If you support
placing it on the Standards Track also consider if it is an update to
RFC 6790.

Please send your comments to the MPLS wg mailing list ( mpls@ietf.org<mailto:mpls@ietf.org> ).

/Loa
for the mpls wf co-chairs

PS

I'm copying the spring working group on this mail.
--

Loa Andersson                        email: loa@pi.nu<mailto:loa@pi.nu>
Senior MPLS Expert
Bronze Dragon Consulting             phone: +46 739 81 21 64

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