In the presence of multiple WiFi networks, it is often desirable to select a particular network to connect. In Mac OS X, the last connected network is automatically selected for connection whenever the Mac restarts or wakes up from sleep. This default choice can easily be changed and you can specify your preferred WiFi network and set it as default.
In OSX Mountain Lion:
- From the Apple Menu select System Preferences - > Network
- In the WiFi Pane select Advanced
- Select the WiFi tab. From the list of Preferred Networks, drag the preferred network and drop it to top of the list. This now becomes the default WiFi network.
The order of networks in the list determines the connection priority; highest priority is assigned to the top name.