Realtek 8129/39 Duplex ?

Donald Becker
Fri Apr 30 03:15:10 1999

On Thu, 29 Apr 1999, [Unix Admin(] wrote:

> Can anyone reccomend a way to check the duplex mode on my rt8129 based
> 100Bt card. Or a way to force it into half duplex(linux 2.2.6).  I get
> massive amounts of collisions copying from my linux server to my windows
> box(using samba 2.0.3) but much MUCH less colisions copying from windows
> to the samba box.  i forced the windows machine into 100Half duplex and i
> set both card's ROM to half duplex. 

The fact that you recording collisions means that the card is in half duplex
You would normally expect more collisions when on the transmitting
side of a file transfer.

> maybe there is another reason for this problem i'm not sure.  In a 5 day
> period i came close to exceeding 500,000 collisions.
> any help is appreciated.

Collisions are normal in Ethernet.
Unless you are experiencing performance problem, or a very high proportion
of collisions, you shouldn't be concerned.

The rtl8139 hardware (and the driver) counts every collision, up to 16 per
Many chips only count "at least one collision occured with this packet", and
thus those drivers will report a lower collision count for the same network

OTOH, a 16-collision event or an out-of-window collision is an error -- these
should almost never happen on a properly functioning Ethernet.

Donald Becker
USRA-CESDIS, Center of Excellence in Space Data and Information Sciences.
Code 930.5, Goddard Space Flight Center,  Greenbelt, MD.  20771

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