Something like this - but in some other NAT implementation?
http://old.nabble.com/iptables-NAT-with-SACK-%28selective-acknowledge%29-td13671650.html
> -----Original Message-----
> From: Testbed Support for GridPP member institutes
> [mailto:[log in to unmask]]On Behalf Of Rob Fay
> Sent: 30 June 2010 12:25
> To: [log in to unmask]
> Subject: Re: LHCb transfer problem + solution
>
>
> > I'd be interested if applying this sort of tuning to worker
> nodes will have any effect at the other sites that are having
> transfer problems - Brunel, Liverpool, Sheffield and Bristol.
>
> We tried it at Liverpool last Thursday, and sure enough, the
> quality of the
> transfers went into the dark green.
>
> However, I can't quite see how the optimisations would
> explain that particularly
> given the seeming correlation with NAT. Why would NAT cause
> problems just
> because the transfers are taking longer? Wouldn't larger
> transfers, or increased
> contention, also cause problems if that was the case?
>
> So looking at the changes, aside from the changes to buffer
> sizes, there are two
> TCP options turned off, timestamps and selective
> acknowledgements (along with
> duplicate selective acknowledgements).
>
> I tried turning timestamps back on, that made no difference,
> transfers stayed green.
>
> I then tried turning SACK and DSACK back on and we saw a drop
> in quality over
> the next few hours down into the 30-40% orange/yellow range.
> Disabling SACK and
> DSACK saw the quality go back to 100%.
>
> I then restored all settings to defaults apart from SACK and
> DSACK being
> disabled, and all transfers since then have been 100%.
> However, there haven't
> been that many transfers since then, so I don't think I can
> really say with
> certainty that SACK/DSACK are the issue, but the evidence so
> far would appear to
> indicate that may be the case, at Liverpool at least.
>
> --
> Robert Fay [log in to unmask]
> System Administrator office: 220
> High Energy Physics Division tel (int): 43396
> Oliver Lodge Laboratory tel (ext): +44 (0)151 794 3396
> University of Liverpool
http://www.liv.ac.uk/physics/hep/
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