[ previous ] [ next ] [ threads ]
 From:  Fred Wright <fw at well dot com>
 To:  m0n0wall at lists dot m0n0 dot ch
 Subject:  Re: [m0n0wall] Collisions on full-duplex LAN interface
 Date:  Sun, 13 Feb 2005 20:03:44 -0800 (PST)
On Wed, 2 Feb 2005, Chris Buechler wrote:
> On Wed, 2 Feb 2005 11:17:16 +0100, Anders Nordström <and at telia dot com> wrote:
> > I'm worried about the collisions on my LAN interface, since it's full duplex
> > and connected to a gigabit switch. I've read somewhere that there could be
> > problems with the Realtek 8029 chipset, which this NIC has. Could that be
> > it?
> > 
> The reason is because it's not full duplex.  According to the ed(4)
> man page, the full duplex mediaopt isn't available on that driver. 

Actually, it doesn't explicitly state that full duplex isn't supported; it
just doesn't mention it at all.  And actually, that part is claimed to be
handled by the miibus driver.

> Most every ed-based card I've seen has a coax port in addition to
> RJ45, and coax can't do full duplex, so my educated guess would be the
> chipset doesn't support full duplex at all (the driver doesn't, at a
> minimum).

It wouldn't be a good guess in principle, since pretty much any chip that
uses MII (and some that can't) can interface to coax with an appropriate
PHY and transceiver.  The typical obstacle to full duplex is that early
chips (e.g. the 7990) shared some logic (e.g. CRC) between transmit and
receive.  Newer chips usually support it, but 10Mb-only chips rarely (if
ever) support autonegotiation, and inexpensive switches rarely (if
ever) support full duplex without autonegotiation.

And in any case, the 8029 datasheet claims that it supports full duplex.

					Fred Wright