[ILUG] eth0 timeouts

[Kenn Humborg]

On Wed, Oct 20, 1999 at 03:24:15PM +0100, ruairi at connect.ie wrote:
> Hi all,
> 
> I have a little problem which someone may be able to help me with... when
> ftp'ing between two Linux boxen on a LAN here in the office, I get a timeout
> on one or other of the boxes ethernet interface after about a meg or so of
> the transfer.

You mean that the kernel give an "eth0: timeout" error, or the
transfer actually fails?

If it's the former, check for cabling problems (esp termination
on coax).  Possibly an IRQ conflict?  Check the sources for the
driver for the ethernet card in /usr/src/linux/drivers/net
and also /usr/src/linux/Documentation for any clues.

> I'm thinking that changing the mtu from it's default value of 1500 to
> something else might help, but I don't know what an appropriate value to
> change it to would be.   Or of course I COULD be barking up the wrong tree
> altogether....

There is one scenario where that could solve it:  It's possible that 
a cable fault (or lack of termination) is causing the frame being 
transmitted to be reflected back along the cable and collide with
itself at the transmitter.  The card should spot this collision, 
stop transmitting, wait a bit and try again.  If the fault is 
persistent, then this collision will happen every time it transmits.
The card won't interrupt the CPU to say that the frame is transmitted
successfully, and the driver in the kernel gives up waiting for this
interrupt and logs the timeout error.

Reducing the MTU will result in smaller frames being transmitted
onto the wire, possibly short enough that the whole frame gets 
put on the wire before it bounces off the fault and comes back again.
Then the ethernet card will think all is OK.

Of course, this would just be covering up the problem, not solving
it.

Later,
Kenn