I lost connection to xbox live a few days ago and I haven't been able to log back on since. Every time I try I get a MTU failure, now I have contacted both Microsoft and Linksys and they both have tried multiple things to help me, but nothing has worked. My computer which is hooked up to the same router works, as does my mothers computer who uses the wireless connection. I have a WRT54GS router, and I thought this might be the problem, but when I connect the Xbox360 directly to the modem I still get a MTU failure. I have tried everything suggested to me by Microsoft and Linksys from restarting the modem and router, and updating the firmware. If anyone has any suggestions please let me know, but I'm no computer expert and would ask kindly that you explain things as simple as possible.
Well, as you get the same error when you connect the xbox directly to the modem it seems more like a modem related issue. Are you sure the modem is only a modem and does not also have some routing functions? Please make this modem check. If your modem is also a router you have to adjust the MTU on the modem/router.
I will advise you to have a word with your internet service provider ..... so that they can do required settings on the Modem ..... once the error is gone after connecting to modem ....we can work on router settings.....
The IP address on the Xbox behind the modem is probably something like 192.168.*.*. This means you have a modem with routing functions (or a router which includes the modem). At the moment, this modem/router is the device which connects to the internet. You have to set the MTU there. You should probably contact your ISP about this and find out what you can do to change the MTU.
The alternative would be to ask the ISP how you can put the modem into "bridge" mode, i.e. turning off the routing functions. Also ask, what settings you need on your router after this change to connect to the internet. You'll probably need PPPoE and your username and password with the ISP. After this change, the Linksys router is the device connecting to the internet and thus the MTU changes on the Linksys router become relevant.