Xbox live MTU error.?

I recently purchased a xbox live wireless router for my xbox 360. I hooked it up and it says that it is able to connect from my Xbox to my wireless router, but it is unable to connect from the router to the Internet. After that it says MTU error. Then I click cancel and it says that the live status is up( service,... show more I recently purchased a xbox live wireless router for my xbox 360. I hooked it up and it says that it is able to connect from my Xbox to my wireless router, but it is unable to connect from the router to the Internet. After that it says MTU error. Then I click cancel and it says that the live status is up( service, marketplace, matchmaking.....) it says the Internet is not connected and xbox live is not connected. I do not know how to fix this problem. I tried moving it closer to the router (right next to the router) and I got the same message. I need a step by step solution. I am open to buying something if it for sure going to fix the issue. I do not have a very good bandwidth and I was wondering if buying a new modem would fix the problem. Any help is appreciated. Thanks
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