OS X supports all sorts of network connections. Wi-Fi, Ethernet, Ethernet over Thunderbolt and iOS tethering via USB and Bluetooth are all available to the modern Mac user.
What you may not know, however, is that you can manually set the priority with which these connections are treated.
Take my MacBook Air, for example. At work, I use the Wi-Fi in my office, but at my desk, I want to use Ethernet via my Belkin Thunderbolt Express Dock to connect to our network for faster file transfers to our local server. At home, I also use wireless, but often plug into my wired network via Apple’s Thunderbolt to Ethernet adaptor.
To do this, I re-ordered my service order to ensure Ethernet would come first, regardless of how it’s physically connected to my device.
Doing so is easy. In the Network preference pane’s Action menu, there’s an item named “Set Service Order.”
Picking that item will bring up a small sheet that allows users to drag-and-drop the available network connection easily:
(It can even be set by Location, but that gets crazy.)
The ordering works from top to bottom. If the first connection type isn’t available, your Mac moves to the next one, and so on. For me, this means that if Ethernet is connected, I can trust I’m using it, and not the wireless network I may also be connected to.