How can I configure my Ethernet connection when booting from Recovery HD?
The expected graphical settings are not provided from the recovery image, but you can find terminal in the Utilities folder and use ipconfig to set a manual IP address and net mask for any active interface.


  ipconfig set en1 manual 192.168.3.1 255.255.255.0


As long as your Wi-Fi isn't connected, you should have a valid route, but you could also set a default route if needed using that command as well.