How do I add ethtool settings to a network device permanently?

ethtool can be used to set options for many types of Ethernet devices. The /etc/sysconfig/network-scripts/ifcfg-ethX files can have the ethtool settings added to them so that the settings are saved and used every time the device is activated.

For example, the command:
ethtool speed 100 duplex full autoneg off

sets the eth0 device to 100Mbs, full duplex, with auto negotiation off. To have the initialization scripts set this every time the eth0 device is activated, add a line to the /etc/sysconfig/network-scripts/ifcfg-eth0 file:

ETHTOOL_OPTS="speed 100 duplex full autoneg off"

source: https://sysadmincorner.wordpress.com/category/linux/networking/