10G switch drops traffic for a split second

Marian Ďurkovič md at bts.sk
Thu Dec 1 11:14:24 UTC 2016

On Wed, Nov 30, 2016 at 11:58:06AM -0500, Lee wrote:
> On 11/30/16, Mikael Abrahamsson <swmike at swm.pp.se> wrote:
> > If your switch is the typical small-buffered-switch that has become more
> > and more common the past few years, then the entire switch might have
> > buffer to keep packets for 0.1ms or less. So if someone says "flow control
> > off" for 0.1ms, depending on the implementation, you might then start
> > seeing packet drops on all ports until that device turns flow control
> > back on.
> I always disabled flow control on the theory that VoIP & flow control
> are incompatible.
> just out of curiosity - anyone have it enabled?  if so, why?

Generally speaking, allowing any ethernet switch to *send* PAUSE frames is very
bad idea, causing external head-of-line blocking and congestion spreading.

OTOH, a decent use-case of flow control is for subrate services.
For example, 622 Mbps microwave link with gigabit ethernet interfaces
ultimately needs to use flow control to properly inform the connected
equipment that this is only "622M ethernet" link and not a gigabit one.


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