I have a wired connection over CAT-5E cable from the gameroom to my Linksys WRT54G router in the living room, and my Internet provider is AT&T, with a 3MB maximum download rate.
The gameroom jack is located so that I can either plug in a second PC or an XBox 360. (I will probably replace the telephone cable and jack with a second CAT-5E/RJ45 before year-end).
I have configured the router to use a maximum MTU of 1492, down from the default of 1500, to accommodate the XBox. The XBox has a dedicated address (192.168.1.5), so it should not be conflicting with any desktop or notebook PC's already in use.
More often than not, my son complains that he can't connect to XBox Live because the MTU's are too low, according to the Network Settings panel. Every other test passes. A friend at work has suggested recycling my router and DSL modem once a week. For a couple of months that solved the problem, but for the past two weeks it has not.
I just ran some speed tests, and here are the results:
whatismyip.com Chicago to San Francisco, download speed 2561 kbps
whatismyip.com Chicago to New York, download speed 2568 kbps
speakeasy.net Chicago to San Francisco, download speed 2578 kbps
speakeasy.net Chicago to New York, download speed 2569 kbps
My questions are:
1) Does the MTU depend on the download speed?
2) Is there diagnostic software that will tell who is at fault? (XBox network, AT&T Internet connection, XBox console or router)
3) Do you have any suggestions on how to proceed?