Intermittent internet flakiness

My internet connection goes out sometimes, but my wireless network is still up and running. I'm not sure what causes the internet to go out, but when it does, it will be out for about 5 minutes and then will return like nothing happened. I can reboot the router or the modem and that will temporarily fix the situation. Also, I've noticed that if I'm in the middle of downloading something, the download continues, but web browsing doesn't work.

any and all help is appreciated.

thanks.