Re: [spring] WGLC for draft-ietf-spring-segment-routing-policy

["Ketan Talaulikar (ketant)" <[e-mail]>]

Hi Dhruv,

Please check inline below.

From: Dhruv Dhody <[e-mail]>
Sent: 29 April 2021 15:46
To: Ketan Talaulikar (ketant) <[e-mail]>
Cc: James Guichard <[e-mail]>; [e-mail]; [e-mail]
Subject: Re: [spring] WGLC for draft-ietf-spring-segment-routing-policy

Hi Ketan,

Thanks for the discussion. Sniping to -


If a node is identified by multiple addresses, from the point of view of the SR policy they would be considered as different nodes, correct?
[KT] This relates to the computation of SR Policy which is outside the scope of this document. There was some text around computation aspects in an earlier version of the draft that has been moved into draft-filsfils-spring-sr-policy-considerations around the WG adoption time. To answer your question, the endpoint address can be mapped to a node which becomes the tail-end and then path is computed to that node. In that case, multiple addresses may all map to a single node. This would be an implementation aspect.

[Dhruv]: I was thinking from the SR policy identification point of view, i.e. <H1-IP1, color, endpoint> and <H1-IP2, color, endpoint> will be considered as different SR policies even though H1-IP1 and H1-IP2 belong to the same headend H1.
[KT] Yes, they would be different SR Policies.


- Section 2.3, What are the 8-bit values for the Protocol-Origin, is there an existing registry that is used here? Is it - https://datatracker.ietf.org/doc/html/draft-ietf-idr-te-lsp-distribution-14#section-9.4 , should it be listed in this document perhaps?
[KT] These are not code points but suggested default values for the Priority assigned to each protocol. An implementation may use a completely different scheme and/or make theme configurable. I see that https://datatracker.ietf.org/doc/html/draft-ietf-pce-segment-routing-policy-cp-04#section-5.2.2 does not clearly indicate this and perhaps the authors should clarify that the Protocol Origin in that PCEP TLV is used to tweak/signal the Priority value to be used for that particular CP in the tiebreaker.


[Dhruv]: I am referring to this text -

   Protocol-Origin of a candidate path is an 8-bit value which
   identifies the component or protocol that originates or signals the
   candidate path.

Which says that an "8-bit value" identifies the protocol as PCEP, BGP, etc. What you are describing is the priority associated with the protocol. I feel the term "Protocol-Origin" and "Protocol-Origin Priority" is used interchangeably, leading to this misunderstanding.

To confirm, in the example - Candidate-path CP1 <protocol-origin = 20, originator = 100:1.1.1.1, discriminator = 1>. The value 20 identify BGP or the Priority value associated with BGP? I am assuming it is the priority!

In which case some cleanup of text is needed to make things clear.
[KT] I see your point. The use of “priority” and that too inconsistently might be the cause for the confusion. Will clean-up the text around this.


- Section 10, It might be a good idea to acknowledge security considerations from the SR policy architecture point of view: how various SR policy parameters and attributes could be exploited to make a headend to forward the traffic incorrectly. It is better to add details that clearly show that the authors/WG have given it a thought and analyzed the implications.
[KT] As a reminder the SR Policy has been introduced in RFC8402 which covers these aspects of incorrect routing and other challenges associated with source routing. This document is only providing the details of the implementation construct/framework for the SR Policy.


[Dhruv]: In my reading, RFC 8402 security considerations are focused on the data plane and not much on the interaction between the controller and SR nodes where the SR policy architecture comes in.
[KT] This document does not cover the actual protocols used for interactions between controller and routers – that is covered via PCEP and BGP documents.


- Section 11, What is the range of the value for Segment Types? A-Z only? It would be good to be clear about this. With A-K already allocated, worth thinking if this is too restrictive and not future-proof. Perhaps we could think of the value as a string that is currently populated with a single alphabetic character.
[KT] String can become freeform. How about A-Z, then AA-AZ … ZA-ZZ – that should be a large enough space?

[Dhruv]: That works. Maybe you could add this to the table to clearly indicate the range:
L-Z: Unassigned
AA-ZZ: Unassigned
[KT] I’ll try to describe this in the text since the AA-ZZ might not be very clear.


Related question: is there a value in putting aside a few of these for Experimental Use?
[KT] I don’t think so because these are not signaled in any protocol.


- Since the I-D talks about policy configuration, explicit candidate paths, verification, SR-DB, etc. I don't want to add work for the authors but I do feel in this case a dedicated manageability consideration section would be useful :)
[KT] Good catch. I will add it. It is not much work really since we need to point to RFC8402 which introduced the SR Policy and an informative reference to draft-ietf-spring-sr-policy-yang that the WG is already working on.


[Dhruv]: That helps, but also think in lines of documenting some key considerations as per https://datatracker.ietf.org/doc/html/rfc5706#section-2
[KT] This is not really a new protocol per-se and I am not sure if this is necessary. However, if there are any text proposals, we can discuss within the WG.

Thanks,
Ketan

Hope the authors and WG find these suggestions useful.
[KT] Yes, definitely.

Thanks!
Dhruv



Thanks,
Ketan

Thanks!
Dhruv
On Fri, Apr 16, 2021 at 12:27 AM James Guichard <[e-mail]<mailto:[e-mail]>> wrote:
Dear WG:

This email starts a 2 week Working Group Last Call for draft-ietf-spring-segment-routing-policy [1].

Please read this document if you haven’t read the most recent version and send your comments to the SPRING WG list no later than April 29th 2021.

If you are raising a point which you expect will be specifically debated on the mailing list, consider using a specific email/thread for this point.

Lastly, if you are an author or contributors for this document please response to the IPR call in the previous email thread.

Thanks!

Jim, Joel & Bruno


[1] https://datatracker.ietf.org/doc/draft-ietf-spring-segment-routing-policy/




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