Re: [sfc] [mpls] Working Group adoption of draft-farrel-mpls-sfc

[Alexander Vainshtein <[e-mail]>]

Stewart and all,
I concur with Stewart with one minor correction: the "simple edge routers" are not the only category of routers that would have problems with imposition of a very deep label stack. And the problem with such stacks goes beyond imposition if effective ECMP is supposed to be used by transit routers, because the labels that carry entropy are located somewhere at the bottom of the label stack and therefore may be not readable by transit routers even if imposition succeeded...

My 2c,
Sasha

Office: [phone]
Cell:      [phone]
Email:   [e-mail]

-----Original Message-----
From: mpls [mailto:[e-mail]] On Behalf Of Stewart Bryant
Sent: Thursday, April 12, 2018 6:04 PM
To: Bernier, Daniel <[e-mail]>; Robert Raszuk <[e-mail]>
Cc: [e-mail]; [e-mail]
Subject: Re: [mpls] [sfc] Working Group adoption of draft-farrel-mpls-sfc


Rather than have a process discussion, I think we should go up a level and better understand the technical differences between the two drafts.

draft-farrel-mpls-sfc describes the actions at a hop in terms of a tuple that mirrors the SFC approach that allows a short indication of potentially re-entrant chains. In its simplest form it uses a compact MPLS stack to describe an arbitarily complex path that is compatile with simple edge routers which are often challenged in terms of the number of labels that they can push.

draft-xu-clad-spring-sr-service-chaining unrolls the path and explicitly calls out each hop and each function into the label stack. This results in a much larger MPLS label stack that will challenge some edge routers. 
The way that we generally deal with imposition limits is through the use of binding-SIDs, which in the limiting case resolves to the approach in draft-farrel with the limitation that the position on the path is implicit in the label stack size rather than explicitly specified by the SI.

Mid-flight path changes (if such things are needed) is clearly simpler with draft-farrel.

The short stack in draft-farrel comes at the cost of greater network forwarding stack, and the long stack is the price that draft-xu-clad pays for the reduction in forwarding state.

The optimal design point between forwarding and control plane state is something that is dependent on many parameters, and is dependent on many network and operational factors, so much so, that don't think it is wise to rule either out of scope at this stage.

The hybrid mode in section 6 of draft-farrel supports the mixed mode in section 7 of the draft. This allows the construction of SFCs that are the concatination of two or more compacted sub-chains. This allows the operator to deploy a solution with the advantages of draft-farrel together with some of the flexibility of draft-xu-clad.

At this stage the two drafts are sufficienly different that I think we need to proceed with both at least to the point where we fully understand the detailed consequences of the two approachs and the scenarios where each finds it's niche.

After developing a better understanding the detail of each design, their control plane, and operational contexts and how each maps to customer network requirements, we can move the drafts to the appropriate IETF track. Such tracks may be anything from abandonment to IETF standard for one or both of these approaches.

Meanwhile I think that we need to focus our efforts on a deeper understanding of the technology and how each might make the Internet work better,  rather than spending effort on arguing about IETF process.

- Stewart

_______________________________________________
mpls mailing list
[e-mail]
https://www.ietf.org/mailman/listinfo/mpls

___________________________________________________________________________

This e-mail message is intended for the recipient only and contains information which is 
CONFIDENTIAL and which may be proprietary to ECI Telecom. If you have received this 
transmission in error, please inform us by e-mail, phone or fax, and then delete the original 
and all copies thereof.
___________________________________________________________________________