I just found out from Xbox Live support that Xbox Live now requires an MTU of 1364 or higher. Unfortunately, my Apple Airport Extreme has no way of changing that setting. This is total crap. Now I literally have to choose between Apple or Microsoft; doing away with my Airport Extreme router or canceling my Xbox Live. And to be honest with you, I believe Microsoft will be winning this battle.
Update – 10/07/2010 6:50pm: I just got off the phone with Apple support to find out if they could tell me the default MTU value on the Airport Extreme since you can’t change it. After waiting on hold for a few minutes for the support technician to research the information they stated the default value is 1492. Stupid Microsoft.
Update – 10/07/2010 7:00pm: I just fixed it myself. Believe it or not, it was a DNS issue. I use OpenDNS on my home network. I have never, EVER had an issue with OpenDNS. I simply went into my Xbox NIC and change the DNS to my ISP’s DNS IP instead of using my router DNS, since it has the OpenDNS IPs, and I was able to log into Xbox Live. Crazy. Although, now that I think of it, I probably could have just put an Allow rule in the OpenDNS settings and it would have fixed it too. Stupid OpenDNS