If you have an intermittent issue, as in it happens on some days and not others, find out if you have your Xbox on a static IP on your home network. If your router is capable of it, doing this will assure that the Xbox uses the same IP each time with its port settings you have saved. If not, it is possible that the IP with the port settings is being assigned to another device randomly on some days. I had the same issue last year when I first set up. Some days good, some not. When I did the static IP there were very few issues after.