[plug] Network Issues (Full/Half Duplex?)

[Craig Ringer]

On Sun, 2004-11-07 at 15:10, Timothy White wrote:

> Now that I have a few more Linux boxes (and converted a few windows 
> boxes) I have discovered the real problem and why it worked at one stage.
> [1]Basically ALL my Linux boxes where running at half duplex with some 
> at 10Mb[2] and some at 100Mb. The problem computer was at 100Mb.

100Mb/s half duplex is relatively uncommon, so I guess compatibility
problems could arise with cheap equipment.

Is there any chance the machine in question has a RealTek 8139A or 8319B
based NIC? If so ... upgrade it to a revision D or later, they're
something like $10. The A and B were OK, but I've found some issues with
them and particular switches / other NICs, plus they can only do
half-duplex.

OK, you mention your NIC below. My advice still stands, though - get an
8139D or later.

>  I could 
> easily send a file to the 10Mb computers as the hub forced the sending 
> computers to go slower. For the 100Mb computers it would fail as they 
> could recieve at high speeds but where of course half duplex which lead 
> to lots of packet collisions and the slow down.

> It appears to me that I ether need to get my Linux box to work at Full 
> Duplex. Does anyone else know another way to fix it?

You shouldn't have to - if a 100Mb/s full duplex device can't talk to a
100Mb/s half duplex device via a switch, you have driver / hardware
problems or a crap switch.

> It is a  3Com Corporation 3c905C-TX/TX-M [Tornado] (rev 6c) and from 
> what I have read the driver is broken and that is why it won't go into 
> Full Duplex. Does anyone have a fix (with out putting all the computers 
> on a 10Mb HD hub)?

I'd get a RealTek 8139 revision D or later. They're cheap, but seem
reliable and perform well. If it doesn't fix your problem, you have
eliminated one possible cause, you have a spare NIC, and doing it only
cost you ten bucks.

By the way, it would be really helpful if you could mention the NICs in
use, the drivers used with each, and the manufacturer and model of the
switch.

>  Works:
> Windows -> 100Mbs FD Switch -> Linux 10Mbs HD
> Windows -> 100Mbs FD Switch -> Linux 100Mbs FD
> Linux 10Mbs HD -> 100Mbs FD Switch -> Linux 100Mbs HD
> Windows -> 100Mbs FD Switch -> 10Mbs HD Hub -> Linux
> Linux -> 10Mbs HD Hub -> 100Mbs FD Switch -> Linux 100 Mbs HD
> 
> Doesn't Work:
> Windows -> 100Mbs FD Switch -> Linux 100Mbs HD
> Linux 100Mbs FD -> 100Mbs FD Switch -> Linux 100Mbs HD
> 
> So basically.
> 100Mbs FD -> 100Mbs HD doesn't work without a 10Mbs HD hub in the line

Sounds to me like you might have a garbage switch or the
hardware/drivers on the half-duplex 100Mb/s linux box might be
braindead. I'd replace the NIC in that box first, and failing that
upgrade the switch - but then, I find replacing hardware worthwhile in
terms of saved time. You may not.

--
Craig Ringer