I just received my new S5D9 board and realized I'd have to plug it into an ethernet port somewhere. To get from my work space to our router, I'd need at least 100 feet of cat 5 cable. The prospect of tacking that around doorways and down halls was not appealing.
There are many solutions to this problem. Powerline adapters work well, but I no longer have any, and they are expensive. You could share ethernet from a Windows machine with an ethernet port, but I didn't want to be required to have my computer on or even here all the time that the S5D9 board was running. Dedicated wifi to ethernet adapters are also available.
I had a Raspberry Pi 2 with a USB wifi dongle sitting around unused because I now use the Pi 3. I thought I'd see if it was possible to configure it to share its wifi internet connection over the ethernet port. Indeed it is. Here is a great tutorial which clearly explains the somewhat complicated series of steps involved.
I tried a few other sets of instructions I found on the web and they didn't work. This tutorial was updated for the Pi 3 but it works perfectly on my Pi 2 with USB wifi dongle. Once this is all set up, you can run the Pi headless and it provides ethernet to the S5D9 board. Just for fun, I also powered the S5D9 from the Pi, and it worked well. I could even see all of the files in the drive. This makes for a very low power and quite portable solution.
I'm still figuring out all of the Linux networking details in the above tutorial (which I had nothing to do with). Basically the Pi becomes a DHCP sever on its ethernet side and shares its wifi internet connection with the new network which in this case consists only of the S5D9 board.