Re: [mpls] [spring] to progress draft-cheng-spring-mpls-path-segment

Loa Andersson <loa@pi.nu> Sat, 23 February 2019 02:16 UTC

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To: Rakesh Gandhi <rgandhi.ietf@gmail.com>, Greg Mirsky <gregimirsky@gmail.com>
Cc: Weiqiang Cheng <chengweiqiang@chinamobile.com>, mpls@ietf.org, spring <spring@ietf.org>, Alexander Vainshtein <Alexander.Vainshtein@ecitele.com>, draft-cheng-spring-mpls-path-segment@ietf.org, Stewart Bryant <stewart.bryant@gmail.com>
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From: Loa Andersson <loa@pi.nu>
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Subject: Re: [mpls] [spring] to progress draft-cheng-spring-mpls-path-segment
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Rakesh, authors,

I have not been thinking about this too much. But if you look at fig 2
of draft-cheng-spring-mpls-path-segment, and you need a GACh between
A and D, I'd say that the GAL will be at the bottom of stack.

What if you need the CACh for the sub-path B to C, where will the GAL
go?

/Loa



On 2019-02-23 09:25, Rakesh Gandhi wrote:
> Hi Greg,
> 
> I am not sure if the question has been answered. I would think GAL is at 
> the bottom of the label stack.
> 
> Thanks,
> Rakesh
> 
> 
> On Sat, Feb 16, 2019 at 4:24 PM Greg Mirsky <gregimirsky@gmail.com 
> <mailto:gregimirsky@gmail.com>> wrote:
> 
>     Hi Weiqiang Cheng,
>     thank you for your expedient response to my questions. The document
>     states that one of the use cases for the Path segment is to be used
>     as a performance, packet loss and/or delay, measurement session
>     identifier. I think that RFC 6374 is the most suitable for PM OAM in
>     SR-MPLS environment. Of course, the type of the encapsulated message
>     can be identified using the destination UDP port number with IP/UDP
>     encapsulation. But another option is to use G-ACh encapsulation.
>     That would require the use of GAL. And that is how I've arrived at
>     my original question (I should have explained it better, my apologies):
> 
>         How the Path segment and GAL are placed relative to each other
>         in the SR-MPLS label stack?
> 
>     Regards,
>     Greg
> 
>     On Fri, Feb 15, 2019 at 4:40 PM Weiqiang Cheng
>     <chengweiqiang@chinamobile.com
>     <mailto:chengweiqiang@chinamobile.com>> wrote:
> 
>         Hi Greg,____
> 
>         Thanks a lot for your comments.____
> 
>         My comments are in-line.____
> 
>         __ __
> 
>         B.R.____
> 
>         Weiqiang Cheng____
> 
>         __ __
> 
>         *发件人:*Greg Mirsky [mailto:gregimirsky@gmail.com
>         <mailto:gregimirsky@gmail.com>]
>         *发送时间:*2019年2月15日3:37
>         *收件人:*Alexander Vainshtein
>         *抄送:*spring@ietf.org <mailto:spring@ietf.org>; Stewart Bryant;
>         draft-cheng-spring-mpls-path-segment@ietf.org
>         <mailto:draft-cheng-spring-mpls-path-segment@ietf.org>;
>         mpls@ietf.org <mailto:mpls@ietf.org>; Loa Andersson
>         *主题:*Re: [spring] to progress
>         draft-cheng-spring-mpls-path-segment____
> 
>         __ __
> 
>         Dear All,____
> 
>         I concur with all what has been said in support of the adoption
>         of this draft by SPRING WG. The document is well-written,
>         addresses the real problem in SR-MPLS, and the proposed solution
>         is technically viable.____
> 
>         My comments and questions are entirely for further discussion:____
> 
>           * would the draft be expanded to demonstrate how "the Path
>             Segment may be used to identify an SR-MPLS Policy, its
>             Candidate-Path (CP) or a SID List (SL)"?____
> 
>         [Weiqiang] Yes, It is necessary and we will add some text to
>         demonstrate this in the future version. ____
> 
>           * as many use cases for the Path Segment are related to OAM
>             operations, it would be helpful to expand on the use of GAL
>             and the Path Segment.____
> 
>         [Weiqiang] It is always helpful to have more use cases. However,
>         The GAL is used today in MPLS-TP LSPs to flag the G-Ach and is
>         used for OAM packets only while the Path segment is used for
>         data packets for the each traffic flow. It is a little bit
>         different. ____
> 
>         Regards,____
> 
>         Greg____
> 
>         __ __
> 
>         On Thu, Feb 14, 2019 at 1:12 AM Alexander Vainshtein
>         <Alexander.Vainshtein@ecitele..com
>         <mailto:Alexander.Vainshtein@ecitele.com>> wrote:____
> 
>             +1.____
> 
>             ____
> 
>             I have been following this draft from its -00 revision. The
>             current revision has resolved most of the issues I (and
>             others) have been raised (e.g., elimination of excessive
>             options).____
> 
>             ____
> 
>              From my POV, in its current state the draft meets two basic
>             requirements for the WG adoption:____
> 
>             1.It addresses a real and relevant problem, namely the MPLS
>             Flow Identification problem discussed in general in RFC 8372
>             <https://tools.ietf.org/html/rfc8372> and scoped to SR-MPLS
>             LSPs in this draft. Specifics of SR-MPLS include the need to
>             provide end-to-end liveness check that is one of the
>             requirements explicitly specified in Section 2 of RFC 8355
>             <https://tools.ietf.org/html/rfc8355>. ____
> 
>             2.It provides a reasonable (from my POV) approach to
>               solution of this problem.____
> 
>             ____
> 
>             I also concur with Stewart’s comment about strong similarity
>             between the approach taken in this draft for SR-MPLS and
>             generic work in progress on synonymous flow labels
>             <https://tools.ietf.org/html/draft-ietf-mpls-sfl-framework-04>
>             that has been already adopted as a MPLS WG item.  To me this
>             is yet another indication that the draft should be adopted.____
> 
>             ____
> 
>             My 2c,____
> 
>             Sasha____
> 
>             ____
> 
>             Office: +972-39266302____
> 
>             Cell:      +972-549266302____
> 
>             Email: Alexander.Vainshtein@ecitele.com
>             <mailto:Alexander.Vainshtein@ecitele.com>____
> 
>             ____
> 
>             -----Original Message-----
>             From: spring <spring-bounces@ietf.org
>             <mailto:spring-bounces@ietf.org>> On Behalf Of Stewart Bryant
>             Sent: Wednesday, February 13, 2019 12:48 PM
>             To: Loa Andersson <loa@pi..nu <mailto:loa@pi.nu>>;
>             spring@ietf.org <mailto:spring@ietf.org>;
>             draft-cheng-spring-mpls-path-segment@ietf.org
>             <mailto:draft-cheng-spring-mpls-path-segment@ietf.org>
>             Subject: Re: [spring] to progress
>             draft-cheng-spring-mpls-path-segment____
> 
>             ____
> 
>             I have just read the draft and agree that it should be
>             adopted by the WG. It solves an important problem in
>             instrumenting and protecting an SR path.____
> 
>             ____
> 
>             It should be noted that we needed to do something very
>             similar in mainstream MPLS via the synonymous label work
>             which is already adopted. ____
> 
>             However SL did not address the SR case.. We therefore need
>             this path label work to be progressed.____
> 
>             ____
> 
>             - Stewart____
> 
>             ____
> 
>             On 10/02/2019 08:11, Loa Andersson wrote:____
> 
>             > Working Group,____
> 
>             > ____
> 
>             > I have reviewed draft-cheng-spring-mpls-path-segment and as far as I ____
> 
>             > can see, it is ready for wg adoption.____
> 
>             > ____
> 
>             > There were some comments in Bangkok, but due to the many collisions ____
> 
>             > between working groups at that meeting I couldn't attend the SPRING ____
> 
>             > f2f.____
> 
>             > ____
> 
>             > The minutes are not clear, but as far as I understand, there is ____
> 
>             > nothing that can't be resolved in the wg process.____
> 
>             > ____
> 
>             > /Loa____
> 
>             ____
> 
>             ___________________________________________________
> 
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> 
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> 
>             https://www..ietf.org/mailman/listinfo/spring____
> 
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-- 


Loa Andersson                        email: loa@pi.nu
Senior MPLS Expert
Bronze Dragon Consulting             phone: +46 739 81 21 64