I have been requested to force my Intel Express Pro cards to be full
duplex 100Mb.

Currently, the interface information says:

$ ifconfig -A fxp0
fxp0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        media: Ethernet autoselect (100baseTX full-duplex)
        status: active
        inet 10.2.1.236 netmask 0xffff0000 broadcast 10.2.255.255
        inet alias 10.2.3.26 netmask 0xff000000 broadcast 10.255.255.255

It is configured (/etc/ifconfig.fxp0) with:
10.2.1.236 netmask 0xffff0000 media autoselect

I was told Qwest's switch is standardized and the switch has auto
negotiation set to off. I was also told that the switch and my NIC cards
will not try to agree on a speed and the NIC has be forced to 100Mb full
duplex or they will get a lot of errors on the switch.

I don't understand this autoselect -- can my interface change after it is
configured? (It is now 100Mb full duplex; can it later become 10Mb or half
duplex all by itself?)

What does this auto negotiation mean?

I was told to try some mii-diag program (which they can provide code that
they know works for Linux boxes). Do I need to hard code a NIC card?

Couldn't I just change it to:
10.2.1.236 netmask 0xffff0000 media 100baseTX mediaopt full-duplex

Thanks for any advice, URLs or other information about
autoselect, autonegotiation and full-duplex. (I already started reading
through ifmedia(4), fxp(4), mii(4) and ifconfig(8).)

(This is under 1.4.2 i386, but I don't think this matters.)

   Jeremy C. Reed
   http://www.reedmedia.net/