The LAN cable coming from the modem should be plugged into the WAN port on the router. Set the Modem to handle PPPOE login and set the router to automatic DHCP configuration. This way you\'re putting the PPPOE on the modem instead of the router. See if that works for your setup.
Also, have you gone into your Xbox and configured the network settings to match that of your network?
I\'d also make sure you\'re running the latest firmware for your router:
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