Re: [Lsr] A question about draft-ietf-lsr-flex-algo

Peter Psenak <ppsenak@cisco.com> Wed, 03 June 2020 12:53 UTC

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To: Huzhibo <huzhibo@huawei.com>, Alexander Vainshtein <Alexander.Vainshtein@ecitele.com>
Cc: "lsr@ietf.org" <lsr@ietf.org>, "draft-ietf-lsr-flex-algo@ietf.org" <draft-ietf-lsr-flex-algo@ietf.org>
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From: Peter Psenak <ppsenak@cisco.com>
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Date: Wed, 03 Jun 2020 14:53:29 +0200
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Subject: Re: [Lsr] A question about draft-ietf-lsr-flex-algo
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Hi Zhibo,

n 03/06/2020 14:40, Huzhibo wrote:
> Hi Alexander, Peter:
> 
>       Thank you very much,After I read the WG alias, I still have a lot 
> of doubts, can we calculate the disjoint path by exclude  SRLG in 
> flexalgo? In fact, unless you previously defined two disjoint planes 
> using SRLG, you cannot guarantee that different FlexAlgo can calculate 
> disjoint paths.

the point is that if you did provide such path, flex-algo can calculate 
them. As I mentioned earlier, this use case came from the field, so 
people out there apparently have such topologies and SRLG assignments.

At the end of the day, use of any of the FAD constraints is optional. 
Look at them as lego blocks - if they fit to your network, use them, if 
they don't, leave them alone.

thanks,
Peter

> 
> Thanks
> 
> Zhibo Hu
> 
> *From:*Alexander Vainshtein [mailto:Alexander.Vainshtein@ecitele.com]
> *Sent:* Wednesday, June 3, 2020 8:19 PM
> *To:* Huzhibo <huzhibo@huawei.com>; Peter Psenak (ppsenak) 
> <ppsenak@cisco.com>
> *Cc:* lsr@ietf.org; draft-ietf-lsr-flex-algo@ietf.org
> *Subject:* RE: A question about draft-ietf-lsr-flex-algo
> 
> Hi Zhibo Hu,
> 
> Welcome to the club - I have already asked the same question and got a 
> response from Peter.
> 
> You can find the relevant email thread here 
> <https://mailarchive.ietf.org/arch/msg/spring/wvowYz7mOwR9f6je46qPV_pD9pU/>.
> 
> My 2c,
> 
> Sasha
> 
> Office: +972-39266302
> 
> Cell:      +972-549266302
> 
> Email: Alexander.Vainshtein@ecitele.com 
> <mailto:Alexander.Vainshtein@ecitele.com>
> 
> *From:*Lsr <lsr-bounces@ietf.org <mailto:lsr-bounces@ietf.org>> *On 
> Behalf Of *Huzhibo
> *Sent:* Wednesday, June 3, 2020 3:07 PM
> *To:* Peter Psenak (ppsenak) <ppsenak@cisco.com <mailto:ppsenak@cisco.com>>
> *Cc:* lsr@ietf.org <mailto:lsr@ietf.org>; 
> draft-ietf-lsr-flex-algo@ietf.org <mailto:draft-ietf-lsr-flex-algo@ietf.org>
> *Subject:* [Lsr] A question about draft-ietf-lsr-flex-algo
> 
> Hi Peter:
> 
> I noticed that draft-ietf-lsr-flex-algo-07 adds exclude SRLG TLV. SRLG 
> defines a group of risk-sharing link groups. It is generally used to 
> prevent the primary and standby paths from passing the same risk-sharing 
> link group .I don't know why a group of SRLG links should be excluded 
> from the FlexAlgo calculation. What is its usecase?
> 
> Thanks
> 
> Zhibo Hu
> 
> 
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