My xbox live doesn't work right. Please help!?

Okay, so this is extremely frustrating. When I am up at college, I can play my xbox fine. I can play with anyone, anytime. When I am at home and bring my xbox home, I can't play with half of my friends. It keeps saying "can't connect. may be network problems" and I know it's because of my connection. I have a stupid Belkin Router, and I watched some youtube tutorial on how to open NATS. I enabled NATS and opened them. HOWEVER, after doing that, my xbox quit letting me connect to xboxlive. It kept saying change my MTU settings to 1364 or higher. Once again, I accessed my Belkin Router and it said my MTU setting was 1454. So I don't understand what the problem is. It's reallyyyyyy frustrating!