Re: [LAD] Strange network problem ?

On Wed, Mar 11, 2009 at 11:35:15AM +0100, Bengt Gördén wrote:

> > Anyone an idea as to what is happening here,
> > and how it could be cured ?
>
> I can't say that I can help you but 19 years as a network engineer can come in
> handy.
>
> The most obvious is that the network is overloaded in some way. Doesn't need
> to be in terms of bandwidth. It can be things like spanning-tree going
> heywire in switches. Redirects is another thing that comes to my mind. A
> sophisticated (there are things like slow pings of IPv6 addresses that fills
> up the table in a switch) DoS might also be the case.
>
> If we assume it's the network that causes the problem you obviously have the
> switches and the routers that can cause the problems not to say firewalls.
> What network set up (equipment and such) do you have?
>
> Is the network protected in some way?

I'll make a complete list of all the equipment
next monday (I don't return there before).

The network is completely isolated, there are just
the four WFS computers (and a fifth which was not
being used), and my Thinkpad R51.
Apart from the ssh -X connection the only traffic
are the messages I mentioned before (around 50/s)
and the status reports from the slave computers,
around 60/s for all three added. All messages are
less than an MTU.

> Have you made some performance tests? iperf is handy.
>
> TCP:
> server:> iperf -s
> client:> iperf -c server
>
> UDP:
> server:> iperf -su
> client:> iperf -c server -u

Good tip, will do.

Now you're here you may be able to comment on
another problem: the network adapter in the
master does not receive the multicast messages
it is sending (even if the TX socket has the
IP_MULTICAST_LOOP option set). Chip is Intel
85something, driver e1000e.

Many thanks,

-- 
FA
Laboratorio di Acustica ed Elettroacustica
Parma, Italia
Be quiet, Master Land; and you, Professor,
will you be so good as to listen to me ?
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