As it seems the tap devices receive the messages from BIRD. However, BIRD does not seem to receive the messages sent to it over the tap device.

I described the scenario and the issues I run into in more detail on stackoverflow.

If somebody has some experience with running BIRD over TUN/TAP devices, please take a look here:

http://stackoverflow.com/questions/21001713/linux-tun-tap-unable-to-read-data-back-from-tap-devices

Much thanks to anybody that can provied me with some insights into the issue!