I just received a new Cisco DCP3825 wireless modem from my ISP Shaw Cable. I have not had any problem with getting wireless or wired internet access for any of my computers or cell phones in my house, but even hard wired into the modem I cannot get online with my xbox 360. I have it hooked into the modem with a CAT5 cable, and even after following all the troubleshooting on the xbox network help page I just continously get an "can't obtain an IP address from your router or modem".
I called my ISP and we spent almost an hour checking to make sure that all the ports were open on the modem, trying to assign the xbox a static IP, etc and nothing worked. There were several people in the technical support office who have simply plugged in their xbox to their modem, turned it on and off it went, with no need for additional configuration or anything, so it is very frustrating trying to identify what the exact problem is here.
If anyone has any other suggestions for me, that would be great, as I don't understand why the xbox 360 was working fine with my dlink router one day and then can't get online with the cisco router the next!!