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

[Alexander Vainshtein <[e-mail]>]

Greg,
I do not think that the quoted requirement from the SR OAM Requirements draft is relevant for this discussion, because, from my POV, it does not refer to ability to measure actual traffic carried in a specific SR-TE LSP across a specific link in the transit node. And this is actually what draft-hegde is all about.

I also do not see how SPME (an ill-begotten MPLS-TP construct) is relevant for this discussion.

As for the added state in transit node: From mu POV ability to recognize specific SR-TE Path ID in the label stack of a packet and to update the counters allocated to this SR-TE Path is a forwarding plane state.

My 2c,
Sasha

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From: Greg Mirsky [mailto:[e-mail]]
Sent: Thursday, November 16, 2017 11:15 AM
To: Alexander Vainshtein <[e-mail]>
Cc: draft-hegde-spring-traffic-accounting-for-sr-paths <[e-mail]>; spring <[e-mail]>; Zafar Ali (zali) <[e-mail]>; mpls <[e-mail]>; Xuxiaohu <[e-mail]>; Michael Gorokhovsky <[e-mail]>; [e-mail]
Subject: Re: [mpls] [spring] Special purpose labels in draft-hegde-spring-traffic-accounting-for-sr-paths

Hi Sasha,
many thanks.
I'd point to SR OAM Requirements<https://tools.ietf.org/html/draft-ietf-spring-sr-oam-requirement-03> (regrettably expired):

   REQ#13:  SR OAM MUST have the ability to measure Packet loss, Packet

            Delay or Delay variation using Active (using synthetic

            probe) and Passive (using data stream) mode.



I think that our discussion indicates that OAM requirements document is useful at least for as long as we're developing OAM toolset. And the document will benefit from clarification to reflect our discussion that PM may be performed both e2e and over SPME.



Regards,

Greg

On Thu, Nov 16, 2017 at 4:11 PM, Alexander Vainshtein <[e-mail]<mailto:[e-mail]>> wrote:
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]<mailto:[e-mail]>] On Behalf Of Greg Mirsky
Sent: Thursday, November 16, 2017 4:28 AM
To: Xuxiaohu <[e-mail]<mailto:[e-mail]>>
Cc: draft-hegde-spring-traffic-accounting-for-sr-paths <[e-mail]<mailto:[e-mail]>>; spring <[e-mail]<mailto:[e-mail]>>; Zafar Ali (zali) <[e-mail]<mailto:[e-mail]>>; mpls <[e-mail]<mailto:[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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