Updated from Snow Leopard to Mountain Lion and every time the MB goes to sleep I have to change my location to restore the internet connection. Any ideas why?

I have just updated to ML from Snow Leopard (to be able to use iCloud with my new iPhone 5) and after every time my 2009 MB 13" goes to sleep I have to change location in order to be able to navigate the internet. The connection is made but does not work on navigation. Changing locations enables navigation of the internet. I have three locations 'Automatic', 'Home' and 'Neufbox', my one-month-old ISP-supplied 'box' (router + VOIP telephone). I have never had such problems so I don't remember which location was the default although I am inclined to think it was 'Home'. The MB was delivered on Leopard and I updated to Snow Leopard with no problem. I didn't go to Lion. A friend recommended that I do this latest update because I couldn't synchronise the contacts and calendar from the MB to the iPhone and I hesitated after reading the many reports of inherent problems. I now have great regrets.