So many of you guys are having the issue with connecting to the servers when playing arena or warzone. You get the cannot connect because of fireteam blah blah blah error.I have been having the same issue but today I managed to fix it.
Try opening these ports: 53, 80, 88, 500, 3074, 3075, 3076, 3544, 4500, and 16000.This worked for me!!! After weeks of searching.
I have only tested this on a wired connection but you all can try wireless, as long as you have the right IP Address when port forwarding.I had the usual required ports for XBONE open but once I added 3075, and 3076. BOOM! Flawless gameplay and fast connection speeds.Maybe this can fix other connection issues as well!