An MTU error normally occurs whenever the MTU setting for your Xbox 360 game console is less than what is required. Maximum transmission unit is the maximum amount of data that can be transmitted through a network. There are several factors that can cause an MTU error to occur on your Xbox 360 game console.
Incorrect MTU Setting
The Xbox 360's minimum requirement for the MTU setting is 1,364. Log into your router configuration page and modify the MTU setting. Refer to the manual of your router for specific instructions on modify the MTU setting. Once you are done, restart your Xbox 360, as well as the router and modem. The MTU error should stop appearing by this time.
Issues With the Network
An MTU error may occur because of issues with your network hardware or Xbox 360 game console. Reboot all the devices, including the router, modem and Xbox game console. Wait at least 30 seconds before turning the devices on again. Turn on the modem and router and give them another one minute to refresh. Turn on the game console, navigate to "My Xbox" and select "System settings." Choose "Network settings" and "Wired network" (or the public SSID of the wireless network if you are connecting to a wireless connection). Choose "Test Xbox LIVE connection." The MTU error should no longer appear.
Problems With Your Wireless Signal
If you are connected to a wireless connection, problems with your wireless signal can trigger the MTU error. If you are too far from the access point, try moving to a closer location and see if this yields any improvement. Change the position of the Xbox 360 antenna, get rid of any metal objects that may be getting in the way of the wireless connection and turn off other wireless devices nearby.
Network Port-Related Problem
Because Xbox 360 works with Xbox LIVE servers, you have to make sure that the following network ports are open: Port 88 (UDP), Port 3074 (UDP and TCP), Port 53 (UDP and TCP) and Port 80 (TCP). Log into your router configuration to modify the settings. If you are not sure how, refer to the router's manual for instructions on open the network ports. If you are not the owner of the Internet connection you are trying to connect to, contact the network administrator and ask him or her to open these ports for you.
