I boot into ubuntu and it connects to the Wifi network fine. After about 10-15min the DNS stop resolving any website and a couple of minutes later network-managers tells me that I'm disconnected and tries to reconnect constantly to my router and fails to do it. Upon Ubuntu restart everything works fine for the first 10-15min again. When I boot into Mac OS X everything is fine with the same connection!

How do I restart wifi interface? sudo ifdow wlan0 just tells me that wlan0 is not configured and wlan0 doesn't appear in /etc/network/interfaces either, which I find strange.... (unless network-manager is doing it behind my back).