It looks like I have the same issue as lots of users who have Comcast. Starting Monday, 11/11, I have been unable to maintain an Xbox live connection. Once I turn the Xbox on, it logs in. But very quickly I get disconnected. I have done the modem/router resets, power cycle, cleared the cache on the Xbox. Sometimes when I check network connectivity, it works fine. Other times I get a ICMP error. Other times the error code is 80151909.
In looking at Xbox forums and Comcast forums, it's obviously a Comcast issue. But when I call them, they want to charge me 79.99$ for Level 2 support to "align" my home network. I call BS.
Does anybody have a solution to the problem?