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

[Stewart Bryant <[e-mail]>]

I would like to ask a fundamental question here.

Do we need transit counters for only MPLS-SR, or do we need it for 
MPLS-LDP as well?

If we need it for both, then we need to have this discussion in a 
general MPLS context and not in an MPLS-SR specific context.

At least some of the methods described here would work for both.

Also WRT the proposal to do ingress collection, if nodal paths are used, 
that only tells us the approximate path, not the hotspot which I 
understand to be the original goal.

- Stewart

On 16/11/2017 14:46, Mach Chen wrote:
>
> Hi Stephane,
>
> If you want to do transit measurement, you have to pay some cost. The 
> difference is how large the cost is, one, two or multiple labels.
>
> For E2E measurement, it could be much easier. A single label (could be 
> local or global) is inserted immediately follow the last label of the 
> SR path. Since there is only one label, the path label could be put 
> into the stack at the beginning, no matter whether the measurement is 
> enable or not. With this, it will not affect the entropy.
>
> Best regards,
>
> Mach
>
> *From:*mpls [mailto:[e-mail]] *On Behalf Of 
> *[e-mail]
> *Sent:* Thursday, November 16, 2017 6:49 PM
> *To:* Robert Raszuk; Alexander Vainshtein
> *Cc:* mpls; spring; Clarence Filsfils; 
> draft-hegde-spring-traffic-accounting-for-sr-paths; Michael 
> Gorokhovsky; [e-mail]; Zafar Ali (zali)
> *Subject:* Re: [mpls] [spring] Special purpose labels in 
> draft-hegde-spring-traffic-accounting-for-sr-paths
>
> Hi,
>
> Yes today we do not have any CLI command on any router to get paths 
> statistics for LDP (I mean Ingress to Egress) as LDP is based on MP2P 
> LSPs, so a transit node does not have the knowledge of the source. 
> From an operational point of  view, what we do today is that we 
> collect netflow statistics on core routers, we project the label stack 
> onto the routing with an external tool to get the Ingress to Egress 
> LDP traffic including the mapping of the flows on the links.
>
> Now for RSVP, we do have such statistics as the LSP is P2P and has 
> states on every node.
>
> Robert mentioned correctly that SR-TE (especially with MPLS dataplane) 
> has limited TE features (we cannot mimic all what RSVP does in SRTE 
> without adding too much complexity).
>
> Thus, is it a problem (transit node stats) worth to be solved ? If 
> yes, where do we accept to put the complexity ? For a stats issue I 
> would rather prefer to move the complexity to an external tool that 
> can do correlations or whatever operations rather than getting it in 
> the forwarding plane…
>
> IMO, that’s a “nice to have” problem to solve getting that we do not 
> have this for LDP and we know the limitations of SR-TE MPLS.
>
> However, Ingress stats per SRTE LSP are for sure mandatory to get !
>
> The main drawback I see with the proposed solution is that it mimics 
> what Entropy label does with a solution which is similar and at the 
> same time cannot replace entropy label as the provided entropy is far 
> from being sufficient (this is not the goal I know, but I was looking 
> for potential use case optimizations). So in a network running entropy 
> label and this mechanism, a router will need to find the ELI/EL and 
> hash, then find another special label to build the stats (maybe 
> tomorrow there will be a third one to look at and a fourth one…). That 
> starts to be a big overhead for the forwarding plane.
>
> Brgds,
>
> Stephane
>
> *From:*mpls [mailto:[e-mail]] *On Behalf Of *Robert Raszuk
> *Sent:* Thursday, November 16, 2017 16:23
> *To:* Alexander Vainshtein
> *Cc:* spring; Clarence Filsfils; mpls; Michael Gorokhovsky; 
> [e-mail] 
> <mailto:[e-mail]>; 
> draft-hegde-spring-traffic-accounting-for-sr-paths; Zafar Ali (zali)
> *Subject:* Re: [mpls] [spring] Special purpose labels in 
> draft-hegde-spring-traffic-accounting-for-sr-paths
>
> Folks,
>
> This thread started and the requirements reported clearly stated that 
> all what we need is the ability to account per path traffic on egress 
> nodes.
>
> Now out of the sudden I see requirement popping up to be able to 
> measure per path in transit nodes.
>
> Well you can do it today with SRv6 if your hardware allows or you can 
> do it with RSVP-TE.
>
> SR-MPLS is replacing LDP and adds ability for limited TE. But SR-MPLS 
> never intended to become connection oriented protocol nor architecture.
>
> So I recommend we take a step back here. Or if you like first go and 
> fix basic MPLS LDP LSPs to allow per end to end path accounting in 
> transit nodes then come back here to ask for the same in SR-MPLS. Not 
> the other way around.
>
> Thx
>
> r.
>
> On Nov 16, 2017 16:12, "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
>
> Office: [phone] <tel:+972%203-926-6302>
>
> Cell: [phone] <tel:+972%2054-926-6302>
>
> Email: [e-mail] 
> <mailto:[e-mail]>
>
> *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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