Googling "m0n0wall full duplex" turned up:
http://m0n0.ch/wall/list/showmsg.php?id=43/55"First, if anyone else is having this problem open up http://<yourm0n0ip>/exec.php and use any of
the following commands;
For 10mbps half-duplex: ifconfig bge0 media 10BaseT/UTP mediaopt half-duplex
For 10mbps full-duplex: ifconfig bge0 media 10BaseT/UTP mediaopt full-duplex
For 100mbps half-duplex: ifconfig bge0 media 100basetx mediaopt half-duplex
For 100mbps full-duplex: ifconfig bge0 media 100basetx mediaopt full-duplex
Substituting bge0 for your device name of course
"