Re: [Lsr] WG Adoption Call for "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks" - draft-bonica-lsr-ip-flexalgo-01

Peter Psenak <ppsenak@cisco.com> Thu, 03 December 2020 09:06 UTC

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To: Aijun Wang <wangaijun@tsinghua.org.cn>, "'Acee Lindem (acee)'" <acee=40cisco.com@dmarc.ietf.org>, "'lsr'" <lsr@ietf.org>
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From: Peter Psenak <ppsenak@cisco.com>
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Date: Thu, 3 Dec 2020 10:06:27 +0100
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Subject: Re: [Lsr] WG Adoption Call for "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks" - draft-bonica-lsr-ip-flexalgo-01
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Hi Aijun,

On 03/12/2020 02:31, Aijun Wang wrote:
> Hi, authors:
> 
> Want to confirm one thing:
> 
> Does the mechanism described in this draft support the automatic 
> fallback from “flex algorithm” to the “traditional least-cost algorithm”?

no.

> 
> That is to say, can one prefix exists both in the “flex algorithm” table 
> and “traditional least-cost algorithm” table, the router prefer to 
> forwarding the packet based on the former table, and if not hit, then 
> lookup the latter table?

no.


> 
>  From the context of the document, the answer seems not, or even on the 
> contrary?
> 
> In cases where a prefix advertisement is received in both a IPv4
> 
>     Prefix Reachability TLV and an IPv4 Algorithm Prefix Reachability
> 
>     TLV, the IPv4 Prefix Reachability advertisement MUST be preferred
> 
>     when installing entries in the forwarding plane.

above text is to handle an error case and only associate the prefix with 
the single algo - e.g. algo 0.

thanks,
Peter

> 
> If so, what the value to deploy such flexible algorithm within the 
> network? From my POV, the reason that we want to deploy such mechanism 
> is that we want to differentiate the path(result of flex algorithm) of 
> some traffic from that(result of traditional least-cost algorithm) of 
> most other normal traffic.
> 
> Best Regards
> 
> Aijun Wang
> 
> China Telecom
> 
> *From:*lsr-bounces@ietf.org <lsr-bounces@ietf.org> *On Behalf Of *Acee 
> Lindem (acee)
> *Sent:* Wednesday, December 2, 2020 5:13 AM
> *To:* lsr <lsr@ietf.org>
> *Subject:* [Lsr] WG Adoption Call for "IGP Flexible Algorithms 
> (Flex-Algorithm) In IP Networks" - draft-bonica-lsr-ip-flexalgo-01
> 
> This IP Flex Algorithm draft generated quite a bit of discussion on use 
> cases and deployment prior to IETF 109 and there was generally support 
> for WG adoption. This begins a two week WG adoption call. Please 
> indicate your support or objection to WG adoption on this list prior to 
> 12:00 AM UTC on December 16^th , 2020. Also, review comments are 
> certainly welcome.
> 
> Thanks,
> 
> Acee
>