Interface collisions

William Palfreman william at
Mon Mar 31 08:35:08 PST 2003

On Mon, 31 Mar 2003, Jack L. Stone wrote:

> For the first time within the past few days, I've noticed collisions being
> reported on the public NIC for one of the servers. I'm not sure if it means
> the switch or the NIC is the culprit, so not sure which component may need
> to be replaced.
> Name  Mtu   Network       Address            Ipkts Ierrs    Opkts Oerrs  Coll
> rl1   1500  <Link#2>    00:40:33:5b:bb:5f  6816063     0  7494432     0
> 66977

That is normal for half duplex.  All it means is that you were using
100Mbit full duplex and now you are using either 100Mbit/half duplex or
10Mbit half duplex.

I did think for a minute that you might have a mismatch between a
hard-set full duplex port on the switch, and the nic not being able to -
possibly for cable quality reasons - and then going into 10Mb/half mode.
But don't think that is the case because you would get a terrible
performance hit (down to 500Mbts-ish IME), and many more collisions than
you have, plus lots of error packets.

So, you are either using an old Cisco Cat 5000, in which case you will
need to relay on black magic and illogical combinations of hard setting
and auto-neg on both the switch and nic end, or you have a kinked cable
causing a reflection back, or some other kind of badness - in which case
the switch and nic should both auto-neg down to 10Mb/half, and you
should be fine until you change the cable.  I've had cables like that
for the last three years without problem.

If your rl nic was bad I'd expect it just to fail, rather than dropping
down to half duplex.

Do a big scp transfer over the cable and try to see what speed you
get.  If you are not too far from 100Mb do you care?

W. Palfreman.			I'm looking for a job:
Tel: 0771 355 0354 for my CV.

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