Duplex mode

Donald Becker becker@cesdis.gsfc.nasa.gov
Tue Nov 2 10:01:40 1999

On Tue, 2 Nov 1999, Dirk Raebiger wrote:

> Am Tue, 02 Nov 1999 schrieb Donald Becker:
> >On Tue, 2 Nov 1999, Dirk Raebiger wrote:
> >
> >> I'm using v1.08a of rtl8139 together with linux kernel 2.2.13. The network
> >> administrator at the institute here says that my machine (gollum) sends in
> >> full-duplex mode. This is also what the led of the card says (full duplex).
> >
> >Incorrect duplex is not a typical problem for a rtl8139.
> May be right, I am no wizard on that topic. Can you tell me a apropriate
> place for this?

This mailing list is the correct place to report rtl8139 problems.

> >>>  The chip configuration is 0x10 0x2c, MII half-duplex mode.
> >Then the chip is in half duplex mode.
> But the card's led says, "full duplex"!

The LED might be labeled full duplex.  But the LED output pins may be
programmed to indicate several status conditions.

I'll check out the datasheet later (I don't have a copy right now) to see
what the default output conditions are.

> >Please report the contents of /proc/net/dev rather than the summarized
> >output of 'ifconfig'.
> Inter-|   Receive                                                |  Transmit
>  face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
>   eth0:248148029  483518    1    0    0     0          0         0 176119795  437044    0    0    0 103195       0          0
> b
> >You are getting collisions which is a certain indication that you are *not*
> >in full duplex mode.
> Where can I read about collisions and their sources?

Any description of Ethernet.  Ethernet is half duplex, and collisions are
normal and expected.

A lack of collisions would indicate that you might be full duplex mode,
which uses Ethernet frame format but removes the contention-access aspect.

Donald Becker
Scyld Computing Corporation, and
USRA-CESDIS,   becker@cesdis.gsfc.nasa.gov

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