Re: [Last-Call] Intdir telechat review of draft-ietf-lsr-ip-flexalgo-12

[Antoine FRESSANCOURT <antoine.fressancourt=40huawei.com@xxxxxxxxxxxxxx>]

Hello,

 

Thanks a lot for those clarifications ! I am not quite sure they should be put somewhere in the draft, but I have learnt something.

 

Best regards,

Antoine Fressancourt

 

From: Acee Lindem <acee.ietf@xxxxxxxxx>
Sent: jeudi 1 juin 2023 17:19
To: Peter Psenak <ppsenak@xxxxxxxxx>
Cc: Antoine FRESSANCOURT <antoine.fressancourt@xxxxxxxxxx>; int-dir@xxxxxxxx; draft-ietf-lsr-ip-flexalgo.all@xxxxxxxx; last-call@xxxxxxxx; lsr@xxxxxxxx
Subject: Re: Intdir telechat review of draft-ietf-lsr-ip-flexalgo-12

 

 

On Jun 1, 2023, at 06:54, Peter Psenak <ppsenak@xxxxxxxxx> wrote:

 

Hi Antoine,

thanks for the review, please see my response inline:


On 01/06/2023 11:22, Antoine Fressancourt via Datatracker wrote:

Reviewer: Antoine Fressancourt
Review result: Ready
I have reviewed this document as part of the INT area directorate's ongoing
effort to review all IETF documents being processed by the IESG.
The document, in version 12, is well written. The objectives of the draft are
clearly stated, and relate to the requirement stated in RFC 9350 to describe in
specific document each extension of Flex-Algorithm beyond SR-MPLS and SRv6
data-planes. The draft's structure is borrowed from RFC 9350 and describes
forwarding or operational considerations.
In my view, the document is ready to be published. I only have one minor
comment that the author might ignore as it may stem from my inexperience with
IGP Flex Algorithms. As far as I can tell, the metrics that can be used in
flexalgo can be rather dynamic. Given this dynamicity, what is the policy that
should be adopted in case the metric for a given prefix is updated very
frequently? IGP convergence can take time, and consumes resources on the
routers, and I was wondering if there would be some sort of threshold or
minimum time before an update is considered.

there are three metric types defined in the draft:

1) IGP metric
2) TE metric
3) Min Unidirectional Link Delay

First two are static values configured by administrator.
Third one could be measured, but the min delay mostly reflects the property of the physical layer and should be semi-constant, unless the physical path changes (e.g. re-routing at the optical layer).

RFC8570 that defines the "Min Unidirectional Link Delay" says:

 "Minimum and maximum delay MUST each be derived in one of the
  following ways: by taking the lowest and/or highest measured value
  over a measurement interval or by making use of a filter or other
  technique to obtain a reasonable representation of a minimum value
  and a maximum value representative of the interval, with compensation
  for outliers."

RFC8570 also talks about announcement periodicity and announcement suppression to avoid frequent changes in these values.

On top of what RFC8570 mentions, IGP implementations have SPF throttling mechanisms to avoid too many calculations, even if some originator advertises these values too frequently.

 

 

For example, see https://datatracker.ietf.org/doc/rfc8405/

 

Thanks,

Acee

thanks,
Peter

Nits from the Gen-ART review have been addressed in version 12.

 

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