Example with hme0:
ndd -set /dev/hme adv_100hdx_cap 0 ndd -set /dev/hme adv_100fdx_cap 1 ndd -set /dev/hme adv_autoneg_cap 0
Make kernel parameter changes to preserve the speed and duplex settings after a reboot.
vi /etc/system
Add:
set hme:hme_adv_autoneg_cap=0 set hme:hme_adv_100hdx_cap=0 set hme:hme_adv_100fdx_cap=1
Note: the /etc/system change affects all hme interfaces if multiple NICs are present (e.g. hme0, hme1).
More information: http://www.science.uva.nl/pub/solaris/solaris2/Q4.13.html