It isn't on the users end. It's happening to a lot of people.
I've played games online at my house for years and had 0 problems with my connection. I buy halo 4 and five days later i get locked out of the servers the entire weekend. I've checked absolutely everything, and nothing is wrong on my end. I've deleted my profile, cleared cache, redownloaded profile, checked conn, tried everything and it all checks out, and all weekend i've been locked out.
Is 343 even alive? are they fixing this?