SCO Unix TCP/IP and NFS FAQ
You may be confused because hardware changes have made what used
to be good advice become not so good advice.
Here's the basic problem. 10/100 capable network devices have 5
- 10 Mbs half duplex
- 10 Mbs full duplex
- 100 Mbs half duplex
- 100 Mbs full duplex
- AUTO, which will negotiate one of the above 4 modes
Typically you have a card connected to a 10/100 switch. If both
devices are set to auto, and everything works as it should, then
you end up with both devices set to 100 Mbs full duplex, which is
the fastest possible connection (duplex means that the devices can
"talk" in both directions at the same time).
At one time, most tech folk would say NOT to use auto
negotiation because it was more likely to screw up and leave you
with a substandard connection. That's not usually the case nowadays
but you should understand the underlying possibilities just in
If the speeds don't match, you get no communication at all. You
have no link, and no network.
If the duplex setting doesn't match, you MAY not get
communication at all, but more commonly you get problems: lousy
performance, intermittent dropouts, etc.
This Cisco link goes into more detail: http://www.cisco.com/warp/public/473/46.html
How to check the settings
I can't tell you how to check the settings on your switch or
hub, but you should be able to find that on the web.
For SCO OpenServer, "ndstat -l" will show your current setting.
To change it, see How do
I force the speed or duplex settings of my NIC.
For Unixware, I think it's under Advanced Settings of
For Linux, it's "mii-tool" that can query and set your NIC.
Mac OS X ifconfig can both show and set: "sudo ifconfig en0 mediaopt full-duplex", for example.
Obviously if auto negotiation is not working, you want to
manually set BOTH devices to the best possible speed and to full
duplex. Note that "best possible" might be 10 Mbs if you are a long
distance away: technically both 10 and 100 Mbs are supposedly
limited to 100 meters, but in actual practice 10 Mbs can often go
further; 100 Mbs cannot. Don't forget to take patch cables into
account if you are getting close to these limits, and quality can
make the difference here.
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