Re: [Int-dir] Intdir telechat review of draft-ietf-lsr-ip-flexalgo-12

Acee Lindem <acee.ietf@gmail.com> Thu, 01 June 2023 15:19 UTC

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From: Acee Lindem <acee.ietf@gmail.com>
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Date: Thu, 01 Jun 2023 11:19:10 -0400
In-Reply-To: <5c1b18f3-a834-f8eb-9755-715f6b0c8795@cisco.com>
Cc: Antoine Fressancourt <antoine.fressancourt@huawei.com>, int-dir@ietf.org, draft-ietf-lsr-ip-flexalgo.all@ietf.org, last-call@ietf.org, lsr@ietf.org
To: Peter Psenak <ppsenak@cisco.com>
References: <168561134224.9013.2692506261437440094@ietfa.amsl.com> <5c1b18f3-a834-f8eb-9755-715f6b0c8795@cisco.com>
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Subject: Re: [Int-dir] Intdir telechat review of draft-ietf-lsr-ip-flexalgo-12
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> On Jun 1, 2023, at 06:54, Peter Psenak <ppsenak@cisco.com> 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.