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

[Robert Raszuk <[e-mail]>]

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]> 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] <+972%203-926-6302>

Cell:      [phone] <+972%2054-926-6302>

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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]> 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]
E：[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]>;draft-hegde-spring-traffic-
accounting-for-sr-paths<draft-hegde-spring-traffic-
[e-mail]>;mpls<[e-mail]>;spring<[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]> on behalf of Greg Mirsky <
[e-mail]>
*Date: *Wednesday, November 15, 2017 at 11:10 AM
*To: *"[e-mail]" <
[e-mail]>, "[e-mail]"
<[e-mail]>, "[e-mail]" <[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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