[LAD] Strange network problem ?

[Fons Adriaensen]

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 ?