[Alug] Networking Trouble - Any Ideas

Steve Fosdick fozzy at pelvoux.demon.co.uk
Fri Sep 13 00:23:01 BST 2002


Adam,

Thanks for such a quick response.

On Fri, 13 Sep 2002 00:04:50 +0100
Adam Bower <abower at thebowery.co.uk> wrote:

> On Thu, Sep 12, 2002 at 11:53:38PM +0100, Steve Fosdick wrote:
> > At home here I have a notebook and desktop PC and I can connect between
> > them via a hub and everything works but when I try a crossover cable
> > instead I get one way transmission, from the desktop to the notebook.
> > 
> > Thinking it could be a cable fault I connected the cable the other way
> > found (so the pairs in use were the opposite way round) but still the
> > notebook could see packets coming from the desktop and not the other
> > way round.
> > 
> > Does anyone have any tips?
> 
> yeah crossover cables are not actually supposed to work, they do by virtue of
> having the correct wires in the correct place but they are not supposed to
> work. I would give you the exact reasons if i had my Ethernet book at home but
> its at work where i have been "fixing" ethernet things there.

Interesting.  I'd be interested to haer why.

> also did you try tcpdump on both ends to just to make sure things couldn't be
> seen?

No.  They way I diagnosed one way transmission was just to look at the packet counters reported at each end by 'ifconfig' assuming that these work at ethernet level rather than IP level.

When I pinged the notebook from the desktop the TX packet counter went up on the desktop and the RX packet counter went up on the notebook.  When I pinged the desktop from the notebook the TX packet counter went up on the notebook but the RX counter on the desktop stayed at zero.

> and are you sure that one of the cards isn't autonegotiating 10 base and
> the other 100 when you are using the crossover cable?

That's a possibility I suppose.  Perhaps one of those companion diag programs that sometimes come with the network drivers could decode the status value so I can see if this is the case.  If it is then I guess the answer may be to lock down one or both ends rather than rely on auto negotiation.

Steve.




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