I know you want to set em manually, but I'll give these resources anyways. I see no good reason to force settings when auto-negotiation is working, it will usually just cause problems down the road if you move the host to a different switch port or network..
Cisco: Why do Autonegotiation
Having said that...
You can use ethtool
to check or change the settings of your card.
For a more permanent solution that will work at boot time, maybe your NIC supports something like the following options:
i.e. the Intel Pro 1000 card allows you to put the settings in the modules.conf..
As an example, if you install the e1000 driver for two PRO/1000 adapters (eth0 and eth1)
and set the speed and duplex to 10full and 100half, add the following to modules.conf
alias eth0 e1000
alias eth1 e1000
options e1000 Speed=10,100 Duplex=2,1
The 3com Driver allows similar options..
The 3C990 driver supports the following options, which can be
supplied as command line arguments to the insmod command or in the
configuration file. Configuration file on RedHat 6.x is
/etc/conf.modules file. Configuration file on RedHat 7.x is
Unless otherwise stated, all settings take the form of:
force=value [,value ]
value can be
1) 0 [10 Megabit Half Duplex]
2) 1 [10 Megabit Full Duplex]
3) 2 [100 Megabit Half Duplex]
4) 3 [100 Megabit Full Duplex]
5) 4 [Default option: Auto]
Maybe your cards driver allows a similar method of setting the speed and duplex ?
Best of luck to ya.