Re: [Lsr] LSR WG Adoption Poll for "Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints" - draft-hegde-lsr-flex-algo-bw-con-02

Aijun Wang <wangaijun@tsinghua.org.cn> Wed, 26 May 2021 07:11 UTC

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From: "Aijun Wang" <wangaijun@tsinghua.org.cn>
To: "'Tony Li'" <tony.li@tony.li>
Cc: "'lsr'" <lsr@ietf.org>, "'Ketan Jivan Talaulikar'" <ketant@cisco.com>, "'Acee Lindem \(acee\)'" <acee=40cisco.com@dmarc.ietf.org>, <draft-hegde-lsr-flex-algo-bw-con@ietf.org>
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Date: Wed, 26 May 2021 15:11:23 +0800
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Subject: Re: [Lsr] LSR WG Adoption Poll for "Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints" - draft-hegde-lsr-flex-algo-bw-con-02
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Hi, Tony:

 

From: lsr-bounces@ietf.org <lsr-bounces@ietf.org> On Behalf Of Tony Li
Sent: Wednesday, May 26, 2021 12:31 AM
To: Aijun Wang <wangaijun@tsinghua.org.cn>
Cc: lsr <lsr@ietf.org>rg>; Ketan Jivan Talaulikar <ketant@cisco.com>om>; Acee Lindem (acee) <acee=40cisco.com@dmarc.ietf.org>rg>; draft-hegde-lsr-flex-algo-bw-con@ietf.org
Subject: Re: [Lsr] LSR WG Adoption Poll for "Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints" - draft-hegde-lsr-flex-algo-bw-con-02

 

 

Hi Aijun,

 

My suggestion is still not introduce such non-cumulative metric to cumulative based SPF calculation process.

 

Again, what we’re proposing is cumulative.

 

[WAJ] My arguments is that your cumulative proposal (section 4.1.1.1 or 4.1.1.2) can get unexpected result, that is, if there is no manual intervention, the E2E sub-optimal path will be selected. You have also confirmed this in https://mailarchive.ietf.org/arch/msg/lsr/wWoGgwf-Nch0_VxjczZBpLFXyos/, said as below:

 

“Override the metric on B-E-D to be even higher.

 

The point of the bandwidth metric (at least in this incarnation) is not to make hop count irrelevant. It is    to set the metrics relative to the bandwidth so that traffic skews towards higher bandwidths. Hops are still relevant. An operator can adjust the reference bandwidth and add manual metrics to achieve different effects, depending on their precise needs.”

 

The operator must investigate their topology carefully to add necessary manual metric to avoid the unexpected sub-optimal path.  Is it nightmare?

 

 

Best Regards

 

Aijun Wang

China Telecom

 

 

 

 

 

Tony