All, I have an embedded device which has an Ethernet interface and serial port.

I want this device to work like a "router", that is, 
1.The device get IP packet from the Ethernet, it the dest IP is not the device itself. It just foward the packet to the 
serial port.
2. The device get data from the serial port (supposed to be IP packet)  and send this data (IP packet) to Ethernet.
3. The device has its own IP and can response ping and ARP from the Ethernet interface.

Now I have QNX running, Ethernet and Serial port are all OK. So how can I realize the forwarding function? BPF or PF.

I just read the doc for "packet filtering" and has no idea so far.
I will not handle the Ethernet header. So BPF is not necessary?

Thanks in advance for any clues.