QUESTION :
At the office I’ve got a MacBook Pro running Mavericks, connected to a CalDigit base station which provides Ethernet over Thunderbolt. This works perfectly. However, I often have to go to meetings where I need to be connected to WiFi. I’ve been disabling WiFi when at my desk, and re-enabling it when I head to meetings, but I figured there had to be a better way. A bit of googling led me to “Set Service Order” options, but when I tried to do it I saw that both Network Interfaces are enabled at the same time:
An ifconfig grep confirmed it:
Which one is being used for actual internet, or is the answer both? Why does the WiFi connect, even though the Thunderbolt is higher in the service order and is already connected? Is there a way to only get the WiFi to connect when the Thunderbolt is unconnected?
ANSWER :
Your Mac maintains a routing table, which lists which interface it will send packets to, based on the network portion of the ip address. You can view this table by calling netstat -nr from the Terminal (or by using Network Utility).
The route you are most interested in will be “default”. This entry determines where your Mac will send packets intended for a network that isn’t in your routing table.
You will need to know the BSD device name for both your Airport card and Thunderbolt interface though, you can find this on the “Info” tab in Network Utility.
So long as the wired method is connected, no significant traffic will flow on the WiFi. You can turn it off if it makes you happy, but there’s no real need to. When you unplug, the wifi takes over. Other than that, it’s just in keep-alive mode (unless they are two different local networks, in which case traffic destined for the WiFi local network will go there. not the case on your setup, evidently.)