[bess] Re: [**EXTERNAL**] Re: Re: Inverse multi-layer OAM

["Shah, Himanshu" <[e-mail]>]

Disagree.
We have discussed the motivation (for prioritizing e2e protection over local protection) in the draft.
It serves the purpose without having to disable TI-LFA on each node – not a desirable option.

Thanks,
Himanshu


From: Joel Halpern <[e-mail]>
Date: Thursday, March 20, 2025 at 10:41 AM
To: Greg Mirsky <[e-mail]>, Robert Raszuk <[e-mail]>
Cc: Shah, Himanshu <[e-mail]>, BESS <[e-mail]>, [e-mail] <[e-mail]>
Subject: [**EXTERNAL**] Re: [bess] Re: Inverse multi-layer OAM

It seems rather counter-intuitive to want to try to repair things end-to-end faster than one expects local devices to detect local failures.  The implied information race conditions seem an invitation to trouble.

Yours,

Joel
On 3/19/2025 11:14 PM, Greg Mirsky wrote:
Hi Robert,
I wholeheartedly agree that local and e2e OAM are complementary tools in an operator's toolbox. Usually, a multi-layer OAM is constructed so that e2e provides the network with a safety net. In that manner, local repair of a link failure is expected to restore services before the failure is detected on the e2e level. As I understand it, the proposal uses a different scheme. According to it, e2e network detection is expected to be more aggressive than the link-level OAM. To me, that's an unusual arrangement.
As for performance monitoring, although some performance metrics can be measured spatially to compose e2e metrics, e2e performance monitoring is easier to deploy in many environments.

Regards,
Greg

On Wed, Mar 19, 2025 at 11:21 PM Robert Raszuk <[e-mail]<mailto:[e-mail]>> wrote:
Hi Greg,

I am very much in support of end to end path assurance. And by assurance I mean not only e2e liveness but also e2e loss, delays, jitter etc ...

The main reason is that link layer failures (even if done on every link in the path) does not provide any information about transit via network devices. And those can be subject to packet drops, selective packet drops (brownouts), delays and jitter via box fabrics in distributed systems etc ... So to me even if e2e is slower then local link detection it still very much a preferred way to assure end to end path quality.

Sure some of them is done at the application layer, but then it is done mainly for statistics and reporting. Doing it at network layer opens up possibilities to choose different path (quite likely via different provider) when original path experiences some issues or service degradation which with link by link failure detection is invisible to the endpoints.

I think at the end of the day those two are not really competing solutions but complimentary. And of course end to end makes sense especially in deployments when you can have diverse paths end to end.

Cheers
Robert

On Wed, Mar 19, 2025 at 4:58 AM Greg Mirsky <[e-mail]<mailto:[e-mail]>> wrote:

Hi Himanshu,

Thank you for the presentation of draft-karboubi-spring-sidlist-optimized-cs-sr [datatracker.ietf.org]<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-karboubi-spring-sidlist-optimized-cs-sr/__;!!OSsGDw!J0VAlRE3z-g7qGfCezoeovWitrC4DFYS65Ly4YZq5r_I8SGk56sle4dQAFwya2R17BHyxx6ecg$>. If I understood your response to Ali correctly, the proposed mechanism is expected to use more aggressive network failure detection than the link layer. If that is correct, I have several questions about the multi-layer OAM:

  *   AFAIK link-layer failures are detected within 10 ms using a connectivity check mechanism (CCM of Y.1731 or a single-hop BFD) with a 3.3 ms interval.
  *   If the link failure is detectable within 10 ms, what detection time for the path, i.e., E2E connection failure detection, is suggested? What interval between test probes will be used in that case?
  *   Furthermore, even if the path converges around the link failure before the local protection is deployed, the link failure will be detected, and the protection mechanism will be deployed despite the Orchestrator setting up its recovery path in the network. If that is correct, local defect detection and protection are unnecessary overheads. Would you agree?



Regards,

Greg
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