[nzlug] Network speed

[Nick 'Zaf' Clifford]

As always with these speed measurements, you need to take a lot more
scientific approach to the problem.

There are a number of factors that contribute to a less than optimal
network speed at gigabit+. Another poster has already outlined some of
the limitations of PC architecture (eg PCI bus speed), so I won't
reiterate there, except to say that unless you are dealing with NICs on
a PCI-E bus, you are kidding yourself if you want true gigabit speeds.

But another thing to look at is Jumbograms
http://en.wikipedia.org/wiki/Jumbo_Frames

You should be able to achieve, with proper hardware, OS configuration,
etc, around 900-950 megabits per second direct connection.

As for how fast BSD is as a NAT'ing firewall, you'd probably have to
talk to BSD people about that if it is a limiting factor.
That said, with the hardware you've specified, with PCI-E NICs, BSD
should not be putting a significant reduction in the speed.

Before anyone could actually comment on the numbers you stated, we'd
need to know a lot about your testing environment, but I don't think you
need to start listing exactly what you've done. You can work it out
yourself if you take scientific steps.

I'd start with ignoring everything but PC->cable->PC setup, and figure
out why that is slow.
Use applications such as tcpblast to calculate speed (otherwise you're
calculating disk speed).
Start both systems in runlevel 1 or equivalent, to be sure you have the
whole CPU to yourself.

Once you get the direct connections up to a reasonable speed (I'd say
850Mbps is reasonable) (assuming you have decent hardware to start
with), then put one of your Gigabit switches in the middle, make sure
you don't loose any performance through that.

Then put the BSD firewall in there.

Nick



Andrew Farago wrote:
> Hi guys,
> The scenario is the next
> Two Linux PC with Gigabit NICs, connected with Cat 6 cables.
> The maximum throughput what I could measure was 0.55 Gbps. (Download
> or upload but I never did the two tests in the same time, that maybe
> less.)
> If I made it a little more complicated...
> LinuxPC}-------{switch}------{BSD firewall}------{switch}------{LinuxPC
> Gigabit NICs and Gigabit switches everywhere (not cheap ones)
> connected with Cat6 cables.
> A few simple rules and NAT on the firewall.
> The max speed what I got was 0.35 Gbps.
> I am very-very disappointed. I expected much more. :-(
> Is it a week performance or this is the performance of a "Gigabit"
> network?
> Do you have any experience?
>
> The computers in the tests had 3Ghz P4 processors + 512Mb RAM.
> The test program was the netperf+netserver duo and I performed a
> TCP_STREAM test.
>
> Andrew
>
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