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Re: failure detection


El 17/08/2005, a las 18:08, Paul Jakma escribió:

On Wed, 17 Aug 2005, marcelo bagnulo braun wrote:

FWIW, TCP for instance already provide some form of such signaling see Appendix E.1 of RFC 2461 Of course other ULP don't provide any kind of feedback.

So i guess it would be a better not to fully rely on ULP feedback, but otoh not using the information that some ULP provide seems suboptimal to me. 

1. I said "extra signaling"

2. Note the title of appendix E: "IMPLEMENTATION ISSUES" and
   describes a possible optimisation that can be made if ULP's can be
   modified - it's wholly at the implementation's discretion.

Exploring stuff like path-reachability probing or implementation optimisations via shim<->ULP signalling (which ULP could be IP quite likely btw, not TCP - implementations possibly will have /two/ layers to pass hints through) is fine, but do it as an appendix or an informational document or wait for implementors to experiment.


I guess i agree, since we cannot be sure that all ULPs will provide such feedback, we cannot base the shim failure detection on the existence of such mechanisms, since it would result in limiting the shim applicability to only those ULPs

The path-probing is, imho, mostly a complete waste of time. But an implementation can go wild if it wants.


i am not sure what do you mean by this... i mean, if you don't have a ULP that provides feedback, how can you be sure that the other end is reachable? i mean, i see probing as a last resource to confirm that an outage has occurred (and then a tool to explore alternative paths before diverting the actual data packets)

so, while in multiple occasions it may not be needed and can be skipped, i see probing as a fundamental part of the shim

The potentials of TCP<->Shim signaling are interesting I'll admit. However, again it's an implementation detail

may agree with this, but imho it need to be taken into account when discussing the present topics

regards, marcelo


(and only reason its being discussed is cause of the crazy path-probing stuff).

I note from the archives that I'm not the first person to have cautioned against going down the path-probing route (Joe Abley too).

regards,
--
Paul Jakma	paul@clubi.ie	paul@jakma.org	Key ID: 64A2FF6A
Fortune:
Manly's Maxim:
	Logic is a systematic method of coming to the wrong conclusion
	with confidence.