(Apologies on the double posting, I didn't notice the questions in the sticky thread before and didn't notice any clear way to edit the other post)
Old post:
I can connect to the internet and my PCs fine from the Xbox but as soon as it attempts a connection to XBL, it tells me my MTU size is too small. I've tried all troubleshooting steps. I've restarted my equipment, tried both wired and wireless connections, all XBL ports were already forwarded to my Xbox's static IP (I also tried DHCP just for fun; same issue), etc. My MTU size is 1500.
What now? I just wanted to play Halo D:
Questions:
What Country/State/Province do you live in?
New Brunswick, Canada
Modem brand & model number:
ActionTec R1000H (Bell-Aliant FiberOp 15 down/15 up)
Router brand & model number:
N/A, built into modem
Network Connection Type: Wireless/Wired
Wired, although the issue persists with my dual-band 802.11n adapter
If Wireless, what type of encryption are you using?
N/A (WPA2 personal when testing wireless)
If Wireless, are you using a white or black external adapter, or an internal (Xbox 360S) adapter?
N/A (external black dual-band n when testing wireless)
Things you have tried:
Is UPnP Enabled?
Yes
Is NAT Type Open?
Yes
Any Error Codes you encounter:
None
What type of internet do you have? Cable/DSL/T1/3G?
Fiberoptic
Who is your ISP(Internet Service Provider)?
Bell-Aliant
After you run "Test Xbox LIVE connection" and click on "More info", what is the exact message shown on screen?
"Your network doesn't have a sufficient MTU settings. Xbox LIVE requires a minimum MTU setting of 1364. On your PC, go to your router configuration webpage and set the MTU to auto, or 1364 or higher. If that doesn't work, disconnect your console from the router and connect directly to the modem."
I'd also just like to note that I use XBL almost every day without any problems whatsoever, and no settings have been changed on my end. I am the only one with any control over it (other than my ISP of course).