Ethtool utility is used to view and change the ethernet device parameters.
insert argument command: eth0
eth0 is the network interface, change for other interfaces e.g. eth1...eth2 etc.
insert argument command: -s eth0 autoneg off
insert argument command: -s eth0 speed 100 autoneg off
Note:
changes made at reboot will be lost, to make them permanent you need to add a configuration line in the /etc/conf.d/net file.
example: