Re: cannot fill 100Mbps pipe (over 20ms rtt via netem)?

From: slashdev
Date: Thu May 01 2008 - 18:06:07 EST


On Wed, Apr 30, 2008 at 5:43 PM, slashdev <slashdev@xxxxxxxxx> wrote:
>
> On Wed, Apr 30, 2008 at 5:27 PM, John Heffner <johnwheffner@xxxxxxxxx> wrote:
> >
> > On Wed, Apr 30, 2008 at 5:13 PM, slashdev <slashdev@xxxxxxxxx> wrote:
> > >
> > > On Wed, Apr 30, 2008 at 4:34 PM, John Heffner <johnwheffner@xxxxxxxxx> wrote:
> > >
> > > > On Wed, Apr 30, 2008 at 2:45 PM, slashdev <slashdev@xxxxxxxxx> wrote:
> >
> > > > > i can provide the tcpdump trace. but that too looks ok. i.e. window
> > > > > scale is set to
> > > > > healthy "10" and the receiver does endup opening large window. but i
> > > > > may be missing
> > > > > something.
> > > > >
> > > > > if you need any other information please do ask.
> > > > >
> > > > > i am bit puzzled at the moment :-)
> > > >
> > > > Linux should easily be able to support this "out of the box" these
> > > > days. Can you post the binary tcpdump somewhere?
> > >
> > > http://slashdev.googlepages.com/traces/
> > >
> > > i've added traces for 20ms rtt and normal lan rtt (aka 0ms rtt :-)
> > > let me know if you have trouble accessing them or want any more
> > > information.
> > >
> > > thanks for your help
> >
> > Both traces show lots of packet loss -- enough to cause an equilibrium
> > cwnd of less than 100 KB. With a short RTT, this window is adequate
> > to fill a 100 Mbps pipe, but with even a 20 ms RTT, it's hurting you.
> > I'm not sure where the packet loss is coming from. Possibly an
> > overloaded switch or bad cable?
>
> thanks for the insight. will take a look at my setup and see why that
> should happen. will report back once i am done fixing things at my
> end.

got rid of the 100Mbps vlan. and connected the GigE's back-2-back
using cross-over cable and with 20ms RTT i am able to fill the pipe
nicely. getting ~900Mbps consistently :-)

so it was the packet drop/loss at the switch ports.

thanks a lot for your help :-)
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