Re: [spring] draft-hu-spring-segment-routing-proxy-forwarding-14: Post convergence path

Peter Psenak <ppsenak@cisco.com> Mon, 26 July 2021 20:26 UTC

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To: Shraddha Hegde <shraddha=40juniper.net@dmarc.ietf.org>, "spring@ietf.org" <spring@ietf.org>
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From: Peter Psenak <ppsenak@cisco.com>
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Date: Mon, 26 Jul 2021 22:26:50 +0200
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Subject: Re: [spring] draft-hu-spring-segment-routing-proxy-forwarding-14: Post convergence path
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Hi Shraddha,

On 26/07/2021 22:16, Shraddha Hegde wrote:
> WG,
> 
> Regarding Peter’s comment on the mic that TI-LFA can divert from post 
> convergence path when SRLG is used for computation I would like to clarify > that an operator is expected to do planning for the post convergence
> path accounting for the SRLG failures.

TI-LFA does not always guarantee that backup path follows the 
post-convergence path.

It depends on what is the type of the backup computed and what is the 
actual failure. When the two do not match, we can not guarantee the 
backup path being equal to post convergence one.

An example is when you are calculating a node protecting backup, but the 
actual failure is a link failure, your backup path may not be the same 
as the post convergence one.

thanks,
Peter



> 
> draft-hu-spring-segment-routing-proxy-forwarding-14 is proposing a 
> mechanism which will
> 
> divert the traffic based on nodes being upgraded to support the 
> protection. The paths
> 
> could be quite divergent from post-convergence path and an operator 
> would be expected
> 
> to do planning to ensure these paths have sufficient bandwidth to take 
> on traffic.
> 
> Rgds
> 
> Shraddha
> 
> 
> Juniper Business Use Only
>