Hi,

I have solved my problem.

It is related to the TCP checksum offload function: I am using as embedded platform PCEngines Alix 3d2, that do not support this function (and also qemu virtual machines do not support it).

This patch disable the tx checksum offload and everything now works fine for me!

nice finding ! I looked through kernel source a bit and it seems we can live without that flag (the tun driver also does not set it). I would commit your patch to the repository unless there are objections ?

Regards, Marek