This is what I did, hopefully it will help you.
I called xbox support for the australia region, explained to them the issue throughly.
Tell them that you can play any other game's matchmaking fine and that you can also play custom games, co-op campaign firefight and can connetc to friends in pre-game lobbys on reach but can't join matchmaking.
Tell them that the issue is world wide and you would likethe matter to be escalated.
Tell them that you believe the problem lies in the way the 343i servers communicate with you ip address, and that you believe because of the TU back in October something changed in 343i's MM servers that is causing the servers to not "see" your ip address.
Be firm and persistant, make sure they escalate the matter and be sure to ha,,er home the fact that it is a known world wide issue.
This is what I did, and within 14 hours of doing this the 101ip issue was fixed. That could (and probably is) just coincidence, but its what I did and it got fixed so give it a shot.