Re: [spring] WG adoption call for draft-hegde-spring-node-protection-for-sr-te-paths

bruno.decraene@orange.com Wed, 09 September 2020 15:17 UTC

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From: <bruno.decraene@orange.com>
To: "draft-hegde-spring-node-protection-for-sr-te-paths@ietf.org" <draft-hegde-spring-node-protection-for-sr-te-paths@ietf.org>
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Thread-Topic: [spring] WG adoption call for draft-hegde-spring-node-protection-for-sr-te-paths
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Date: Wed, 9 Sep 2020 15:16:56 +0000
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Subject: Re: [spring] WG adoption call for draft-hegde-spring-node-protection-for-sr-te-paths
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Hi authors, all,

As an individual contributor, I have two non-blocking comments.


1)      I feel that the terminology “node protection”  in the name of the draft could be misleading.


“Node Protection” is already used in [LFA] and [RLFA]. It refers to a property of the alternate path avoiding the next node on the path to the egress/destination. It does not change the destination/egress.
It looks to me that the function been proposed in the draft is more along [Egress Protection] which protects from the failure of the egress/destination, and hence do change the destination/egress. (full disclosure, I’m co-author of [Egress Protection] )

I think that both are different and that properties are different, hence using the same name is misleading.
In particular, in the first one, the destination/egress is unchanged and hence properties of the destination/egress is unchanged: no problem. While in the second case, a node (a ‘protector’ in [Egress Protection]) is claiming to provide a similar service, but possibly only a subset of the original services or without the stateful states). Cf some discussion on the mailing list along “How do I know that I can safely pretend that I’m the original destination?”

Personally I would propose to replace “Node Protection” by “Segment Protection” or “Segment Egress Protection” or “IGP Segment Egress Protection” since the proposal seem restricted to IGP knowledge.

[LFA] https://tools.ietf.org/html/rfc5286
[RLFA node protection] https://tools.ietf.org/html/rfc8102
[Egress Protection] https://tools.ietf.org/html/rfc8679


2)      At best, the proposal ignores [Egress Protection]. At worst, the draft breaks [Egress Protection]

Both do not seem to co-operate. The draft applies the egress protection even though it can only protections IGP segments/labels while [Egress Protection] would provide a much broader protection, including service (e.g. VPNs) protection. Hence it seems to break [Egress Protection] VPN service protection.
I would propose that the draft refers a bit more to [Egress Protection], uses its terminology if/when appropriate and then elaborate on the above issue. From a technical standpoint, I would propose to privilege the use of a (complete) Protector (as per [Egress Protection] ) if available.

Finally, as also raised by Zhibo, the scalability properties of the draft is not optimal, and in particular less optimal than [Egress Protection]. Indeed, most of the work/states is on a Protector node (having the context mpls forwarding table). For a given failure, [Egress Protection] allows for a single Protector while this drafts requires N Protectors (one per neighbour). So more states in the network and on nodes. Also [Egress Protection] allows to distribute this load while the draft requires the PLR to handle the protection for all its neighbhors.
Since this draft restricts to IGP Segments, the scalability impact his limited but still exist.
(on the pro side, the draft avoids the additional transport cost/delay required to reach the Protector (since PLR and Protector are co-located)/

Regards,
Bruno


From: spring [mailto:spring-bounces@ietf.org] On Behalf Of bruno.decraene@orange.com
Sent: Thursday, July 30, 2020 2:25 PM
To: spring@ietf.org
Cc: draft-hegde-spring-node-protection-for-sr-te-paths@ietf.org
Subject: [spring] WG adoption call for draft-hegde-spring-node-protection-for-sr-te-paths

Hi SPRING WG,

Authors of draft-hegde-spring-node-protection-for-sr-te-paths  [1] have asked for WG adoption.

Please indicate your support, comments, or objection, for adopting this draft as a working group item by August 20th 2020. (*)

Could those who are willing to work on this document, please notify the list. That gives us an indication of the energy level in the working group to work on this.

Thanks,
Regards,
Bruno, Jim, Joel

[1] https://tools.ietf.org/html/draft-hegde-spring-node-protection-for-sr-te-paths-07
(*) 3 weeks to account for the IETF meeting week and the august/summer period.


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