debugging slow network

[Roland Smith]

On Sun, Dec 20, 2009 at 01:22:50PM +0000, Anton Shterenlikht wrote:
> I seem to have a very slow network connection at work.
> All local switches are supposed to be gigabit, and my
> network card is gigabit as well. But download speed
> seems to be much lower.

Are we talking download from the internet, or from the local network?

Every time you connect to a server on the internet, your packets travel
through a chain of hosts, routers and switches. And as with any chain, the
weakest (in this case slowest) link determines the strength (speed) of the
chain. Which is unlikely to be your internal gigabit network, unless something
is misconfigured on your end. So it could be that you are expecting too much.

If you are experiencing slow speeds on the internal network, contact the
network admin and ask for help. But make usre that your network hardware is
set up correctly.
 
> I'm not a networks person, but I understand there could
> many factors affecting the speed. 

Definitely.

> There appear to be
> a multitute of different network related commands
> just in base OS. Which should I start with to get
> some idea of the actual network speed? netstat?
> And should I be looking for?
 
As usual, the answer is probably; it depends on what is causing the slow speed.

If the problem is not caused by hardware or software problems on your machine,
you cannot do very much about it by yourself. You need at least the help of your
network admin.

I would start with the ifconfig command. This will show you how your network
hardware is configured. It should list at least two devices, and you should 
ignore one of them, lo0. Look for the lines starting with a lot of spaces and then
'media:'. That should tell you how your ethernet hardware is configured. If it
is running at gigabit speed, you should see something like;

	media: Ethernet 1000baseTX <full-duplex>

If it shows 100baseTX or 10baseT/UTP, you're not getting a gigabit connection
but 100 or 10 Mbits/s.

Also look through /var/log/messages for any logged messages from your ethernet
hardware. 

In my experience a lot depends on the quality of the network hardware and the
drivers. On a 100 Mbit/s point-to-point connection, I've observed throughput
of up to 10 Mbyte/s (12,5 would be the theoretical maximum). This was between
two xl(4) devices. If one of the devices is an rl(4) device, the maximum
throughput speed I've seen is about 4 Mbyte/s (using the same cable and
hardware on the other end).


Roland
-- 
R.F.Smith                                   http://www.xs4all.nl/~rsmith/
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