Do you care about "gray" failures? Can we (network academics) help? A 10-min survey

William Herrin bill at
Thu Jul 8 21:01:12 UTC 2021

On Thu, Jul 8, 2021 at 5:31 AM Saku Ytti <saku at> wrote:
> Network experiences gray failures all the time, and I almost never
> care, unless a customer does.


I would suggest that your customer does care, but as there is no
simple test to demonstrate gray failures, your customer rarely makes
it past first tier support to bring the issue to your attention and
gives up trying. Indeed, name the networks with the worst reputations
around here and many of them have those reputations because of a
routine, uncorrected state of gray failure.

To answer Laurent 's question:

Yes, gray failures are a regular problem. Yes, most of us care. And
for the most part we don't have particularly good ways to detect and
isolate the problems, let alone fix them. When it's not a clean
failure we really are driven by: customer says blank is broken, often
followed by grueling manual effort just to duplicate the problem
within our view.

Can network researchers do anything about it? Maybe. Because of the
end to end principle, only the endpoints understand the state of the
connection and they don't know the difference capacity and error. They
mostly process that information locally sharing only limited
information with the other endpoint. Which means there's not much
passing over the wire for the middle to examine and learn that there's
a problem... and when there is it often takes correlating multiple
packets to understand that a problem exists which, in the stateless
middle with asymmetric routing, is not usable. The middle can only
look at its immediate link stats which, when there's a bug, are

What would you change to dig us out of this hole?

Bill Herrin

William Herrin
bill at

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