YES I HAD THIS PROBLEM . i updated xbox with a flash drive ( downloaded the update from xbox.com ) . then when i tried to connect to live i got ICMP and MTU errors . so i tried test connection a few times .
here is what i did : go to configure network and press " restore to factory settings " .
after that i didn't connect right on that time , i still had the MTU error . but after an hour i turned on my xbox and this time it was connected to live .
Bought an Xbox One yesterday and couldn't download the update no matter what I did. Finally Xbox Support's twitter told me to try an offline update patch, and that managed to go through. Was very frustrating but I've been playing fine now. *Fingers Crossed*