There is an application called ethtool, which allows to modify speed/duplex and several other related settings, but it only works on WAN port since it is a separate physical device. It can be done with the following example command:
- ethtool -s eth1 duplex full speed 100 autoneg off
LAN ports operate as a switch, and currently switch driver doesn't support manually setting link speeds. The switch hardware itself does support the feature, but making use of it would require modifying the switch driver. There are plans to implement this in the future, but no specific timelines are set at the moment.