Re: [gentoo-user] Lots of network collisions - can I eliminate them?

[Mark Knecht]

On 9/23/05, Jonathan Wright <mail@×××××××××.uk> wrote:
> Mark Knecht wrote:
> > 1) What causes a 'collision' on a network interface?
>
> As Paul pointed out via his e-mail (via the previous thread), collisions
> are when two packets try and talk over an ethernet cable at the same time.
>
> In terms of a hub, it's very common, esp. when the hub becomes loaded as
>   2/4/8/32, etc. machines are all essentially using the same bit of
> cable (what with a hub being nothing more than a repeater).
>
> If an interface detects a collision, the transfer is stopped and a it
> waits a random amount of time before trying to send it again. This goes
> round and round until it's sent.
>
> For a switch on the other hand, its not so common, as there are only
> ever two machines on the cable - the switch and the computer. Although
> 31% collision rate on dragonfly does seam alot.
>
> Again, Paul is probably right, with half-duplex being the problem. In
> this case, the same 'cable' us used for both sending and receiving
> traffic. If one conflicts the other, you'll get a collision. With
> Full-duplex, sends and receives are independent and therefore you can't
> get collisions:
>
<SNIP>
>
> > 2) How can I eliminate them? (Including hardware changes if required.)
> > The two machines are connected through a small LinkSys switch. model EZXS55W:
>
> When I first read that I thought 'cheap built-in hub', so only 10MBps @
> HD, however looking at it, 100MBps-FD shouldn't be a problem.

I bought the switch base don it being able to do 100Mb FD. Thanks to
your suggestion about mii-tool I'm not so sure right now that it's
actually doing it...

> A good
> tool to look at is mii-tool (emerge mii-diag):

YES!! VERY HELPFUL! Thanks!

>
> root on jonathan [ ~ ] --> mii-tool
> eth0: negotiated 100baseTx-FD flow-control, link ok

Now, I'm thinking that this is setting the mii on my PC, correct? (Not
on the switch.) Unfortunately it appears that Dragonfly cannot/will
not do 100baseTx-FD or HD!

dragonfly ~ # mii-tool
eth0: 10 Mbit, full duplex, link ok
dragonfly ~ # mii-tool -F 100baseTx-FD
dragonfly ~ # mii-tool
eth0: 100 Mbit, full duplex, no link
dragonfly ~ # mii-tool -F 10baseT-FD
dragonfly ~ # mii-tool
eth0: 10 Mbit, full duplex, link ok
dragonfly ~ # mii-tool -F 10baseT-HD
dragonfly ~ # mii-tool
eth0: 10 Mbit, half duplex, link ok
dragonfly ~ # mii-tool -F 100baseTx-HD
dragonfly ~ # mii-tool
eth0: 100 Mbit, half duplex, no link
dragonfly ~ # mii-tool -F 10baseT-FD
dragonfly ~ # mii-tool
eth0: 10 Mbit, full duplex, link ok
dragonfly ~ # mii-tool -F 100baseTx-FD
dragonfly ~ # mii-tool
eth0: 100 Mbit, full duplex, no link
dragonfly ~ #

dragonfly ~ # lspci | grep Ethernet
0000:01:03.0 Ethernet controller: Realtek Semiconductor Co., Ltd.
RTL-8139/8139C/8139C+ (rev 10)
dragonfly ~ #

Note that there is no link for any of the 100Mb settings. This is
verified looking at the switch itself as the link light turns off.
Actually, I had never noticed that the 100 light was not turning on
before today. so much for plug and play! (My bad...me stupido...) ;-)

dragonfly ~ # mii-tool -v
eth0: 100 Mbit, full duplex, no link
  product info: vendor 00:00:00, model 0 rev 0
  basic mode:   100 Mbit, full duplex
  basic status: no link
  capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  advertising:  100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
dragonfly ~ #

dragonfly ~ # mii-tool -F 10baseT-FD
dragonfly ~ # mii-tool -v
eth0: 10 Mbit, full duplex, link ok
  product info: vendor 00:00:00, model 0 rev 0
  basic mode:   10 Mbit, full duplex
  basic status: link ok
  capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  advertising:  100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
dragonfly ~ #

So far, up to this point, I can at least see the world using
100baseT-FD. That should be better than what I had before. (I
think...)

> root on jonathan [ ~ ] --> mii-tool -v
> eth0: negotiated 100baseTx-FD flow-control, link ok
>    product info: Intel 82555 rev 4
>    basic mode:   autonegotiation enabled
>    basic status: autonegotiation complete, link ok
>    capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
>    advertising:  100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
>                  flow-control
>    link partner: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
>                  flow-control
>
> Then you can run:
>
> root on jonathan [ ~ ] --> mii-tool -F 100baseTx-FD
>
> Which should put the computer into 100MBps via Full Duplex. Give that a
> go - it should work. If there's a problem putting it into that (and you
> can run 'mii-tool -r' to re-negotiate), it may be the switch and/or the
> cable.

dragonfly ~ # mii-tool -r
restarting autonegotiation...
dragonfly ~ # mii-tool -v
eth0: autonegotiation failed, link ok
  product info: vendor 00:00:00, model 0 rev 0
  basic mode:   autonegotiation enabled
  basic status: autonegotiation complete, link ok
  capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  advertising:  100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
dragonfly ~ #

OK, so something is having trouble with this negotiation stuff. I'll
drag out some new cables after I send this and see what happens with
that. I looked at the LinkSys switch docs again. There are no user
settings that I see to get the switch to support 100Mb/S. It's
supposed to be automatic.

Again, thanks very much. mii-tool is very helpful. I'll also have to
look at mii-diag to see if it can help with this problem.

cheers,
Mark

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