Re: [spring] Updating the SPRING WG Charter

[Alexander Vainshtein <[e-mail]>]

Stewart,
Lots of thanks for presenting this issue up front.

I had similar concerns regarding Binding SIDs introducing per-path state in transit nodes.

One possible argument against such a conclusion is that a Binding SID (similar to Adj-SID) can be used by multiple end-to-end paths. So the state it adds is not necessarily a per-path state.

At the same time from my POV elimination of per-path state in transit routers is the main differentiator between the SR and other mechanisms for traffic steering. So I would not hurry to remove the text that you have highlighted.

Regards,
Sasha

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From: spring [mailto:[e-mail]] On Behalf Of Stewart Bryant
Sent: Tuesday, June 19, 2018 2:19 PM
To: Rob Shakir <robjs=[e-mail]>; SPRING WG List <[e-mail]>
Subject: Re: [spring] Updating the SPRING WG Charter




On 01/06/2018 17:05, Rob Shakir wrote:
The SPRING WG defines procedures that allow a node to steer a packet through an
SR Policy instantiated as an ordered list of instructions called segments and
without the need for per-path state information to be held at transit nodes.

I am not sure where the line gets drawn with the per-path state statement. If I introduce a
binding-SID to allow the creation of a path, have I introduced per-path state or not? In practise
a management entity will choose between the infinity of possible binding-SIDs by considering
the need to create specific paths and I would imagine that many will be instantiated just-in-time.

I think that the key point is that the ingress creates the path by using SIDs to create
a concatenation of paths, policies and resources. However it could be argued that
as soon as we introduced Binding SIDs we introduced per-path state. I think we might
be best served by deleting the text I have highlighted.

- Stewart





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