Re: [spring] [mpls] Special purpose labels in draft-hegde-spring-traffic-accounting-for-sr-paths

[Alexander Vainshtein <[e-mail]>]

Greg,
I concur with your position: let’s first  of all agree that ability to measure traffic carried by an SR-TE LSP in a specific transit node is a require OAM function for SR.

I have looked up the SR OAM Use Cases<https://datatracker.ietf.org/doc/draft-ietf-spring-oam-usecase/?include_text=1> draft, and I did not find any relevant use cases there.
The only time measurements are mentioned is a reference to an expired implementation report<https://tools.ietf.org/html/draft-leipnitz-spring-pms-implementation-report-00> draft discussing delay measurements.  Since delay measurements are in any case based on synthetic traffic, and are always end-to-end (one-way or two-way), this reference is not relevant, IMHO, for this discussion.

I have added the authors of the SR OAM Use Cases draft to tis thread.

Regards,
Sasha

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From: mpls [mailto:[e-mail]] On Behalf Of Greg Mirsky
Sent: Thursday, November 16, 2017 4:28 AM
To: Xuxiaohu <[e-mail]>
Cc: draft-hegde-spring-traffic-accounting-for-sr-paths <[e-mail]>; spring <[e-mail]>; Zafar Ali (zali) <[e-mail]>; mpls <[e-mail]>
Subject: Re: [mpls] [spring] Special purpose labels in draft-hegde-spring-traffic-accounting-for-sr-paths

Dear All,
I cannot imagine that operators will agree to deploy network that lacks critical OAM tools to monitor performance and troubleshoot the network. True, some will brave the challenge and be the early adopters but even they will likely request that the OAM toolbox be sufficient to support their operational needs. I see that this work clearly describes the problem and why ability to quantify the flow behavior at internal nodes is important for efficient network operation. First let's discuss whether the case and requirement towards OAM is real and valid. Then we can continue to discussion of what measurement method to use.

Regards,
Greg

On Thu, Nov 16, 2017 at 10:05 AM, Xuxiaohu <[e-mail]<mailto:[e-mail]>> wrote:
Concur. Although it has some values, it's not cost-efficient from my point of view. Network simplicity should be the first priority object. Hence we would have to make some compromise.

Best regards,
Xiaohu



________________________________
徐小虎 Xuxiaohu
M：[phone]<tel:[phone]>
E：[e-mail]<mailto:[e-mail]>
产品与解决方案-网络战略与业务发展部
Products & Solutions-Network Strategy & Business Development Dept
发件人： Zafar Ali (zali)
收件人： Greg Mirsky<[e-mail]<mailto:[e-mail]>>;draft-hegde-spring-traffic-accounting-for-sr-paths<[e-mail]<mailto:[e-mail]>>;mpls<[e-mail]<mailto:[e-mail]>>;spring<[e-mail]<mailto:[e-mail]>>
主题： Re: [mpls] [spring] Special purpose labels in draft-hegde-spring-traffic-accounting-for-sr-paths
时间： 2017-11-16 02:24:10

Hi,

This draft breaks the SR architecture. I am quoting a snippet from abstract of SR Architecture document https://tools.ietf.org/html/draft-ietf-spring-segment-routing-13, which states:
“SR allows to enforce a flow through any topological path while maintaining per-flow state only at the ingress nodes to the SR domain.”

In addition to creating states at transit and egress nodes, the procedure also affects the data plane and makes it unscalable. It also makes controller job much harder and error prune. In summary, I find the procedure very complex and unscalable.

Thanks

Regards … Zafar


From: spring <[e-mail]<mailto:[e-mail]>> on behalf of Greg Mirsky <[e-mail]<mailto:[e-mail]>>
Date: Wednesday, November 15, 2017 at 11:10 AM
To: "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Subject: [spring] Special purpose labels in draft-hegde-spring-traffic-accounting-for-sr-paths

Hi Shraddha,
thank you for very well written and thought through draft. I have these questions I'd like to discuss:

  *   Have you thought of using not one special purpose label for both SR Path Identifier and SR Path Identifier+Source SID cases but request two special purpose labels, one for each case. Then the SR Path Identifier would not have to lose the bit for C flag.
  *   And how you envision to collect the counters along the path? Of course, a Controller may query LSR for all counters or counters for the particular flow (SR Path Identifier+Source SID). But in addition I'd propose to use in-band mechanism, perhaps another special purpose label, to trigger the LSR to send counters of the same flow with the timestamp out-band to the predefined Collector.
  *   And the last, have you considered ability to flush counters per flow. In Scalability Considerations you've stated that counters are maintained as long as collection of statistics is enabled. If that is on the node scope, you may have to turn off/on the collection to flush off some old counters. I think that finer granularity, per flow granularity would be useful for operators. Again, perhaps the flow itself may be used to signal the end of the measurement and trigger release of counters.
Regards,
Greg


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