Alright, so I have successful forwarded all the Xbox Traffic through VPN. However there is a problem regarding MTU. Without the VPN, the Xbox tests the connection and the MTU is 1480. After the OpenVPN connection the xbox test reports an MTU of 1368. The min MTU for xbox to function properly with multiplayer gaming is 1384.
You have set "tun_mtu_extra" to 32 bytes, and that is exactly the difference you are experiencing. I'm no expert and I do not know why you choosed that value, but I would try to lower it and see if everything works.
I have set 'tun_mtu' to 1480 first. then I have tried both lowering 'tun_mtu_extra' to 16 and removing the option. Both still yield MTU 1368. I have also removed the mssfix option. Nothing. I am on a PPPoE connection. I have this option because it was present in the OVPN file by the VPN service provider. Without this option, I notice my speeds are affected drastically.
Assume that the TUN/TAP device might return as many as n bytes more than the –tun-mtu size on read. This parameter defaults to 0, which is sufficient for most TUN devices. TAP devices may introduce additional overhead in excess of the MTU size, and a setting of 32 is the default when TAP devices are used. This parameter only controls internal OpenVPN buffer sizing, so there is no transmission overhead associated with using a larger value.
While I'm not sure exactly where some of the 80 to 100 missing bits are...I believe maybe I can save you 32...
1368 + 32 == 1400
1400 > 1384
Remove option tun_mtu_extra '32' - it will then default to 0.
BTW...I'm not sure about that tun mssfix setting...if I understand the manual, your setting is OK at its default of 1450.