I have been getting this error ever since last sunday afternoon. I was playing rockband 2 and in the middle of a song I was kicked off xbox live. No big deal right, just go re connect after the song is over. I tried to connect and after waiting about a minute see that I can't sign in. My first instinct is go restart the gateway, so I go and do that. After fully restarting it (ie. 5 minutes of letting it sit there powered off) I go and turn it back on and wait for all the lights to turn back on, and all of them do just like normal. I go to sign back on to xbox live, and still no luck. I went back to the dashboard and checked the connection and it said I had to restart my gateway again so I restarted it again. After doing so I tried it again and the it told me my MTU packet size is too small. (Now I'm a pretty tech savvy guy and know my MTU packet size is at 1440-1500 at all times to maximize my ping settings.) This struck me as odd because, I knew my MTU packets were the right size.
Connecting from: Texas, USA
Modem brand: The generic one that Verizon gives (Don't know the name)
Router brand: It is a gateway btw
Internal wireless ie.. the new Xbox 360 S
UPnP is enabled
I have never been open on Xbox live even after being helped by the xbox support team.
I have DSL internet
my ISP is Verizon
My error message is: Your network doesn't have a sufficient MTU setting. Xbox LIVE requires a minimum MTU setting of 1364. On your PC, go to your router configuration webpage and set the MTU to auto, 1364 or higher. If that doesn't work, disconnect your console from the router and connect directly to the modem.