If it is not possible, I would be curious to know what the closest solution would look like pushing the limits of the Rpi's hardware.
Additional information and a concrete example:
I have a Pi connected to wireless internet, with a dynamic IP assigned to its wlan0 interface. Attached to the Pi's eth0 interface is a device that lacks wireless capabilities, but that the Pi gives internet access to via Proxy ARP (and mDNS relaying). That is to say, the device's IP is seen on the network (it's IP given to it by the Pi), but the MAC address associated to that device's IP is the Pi's MAC address.
I would like the open ports of this eth0 device to be linked/forwarded to the Pi's in such a way that the device's IP address is not only visible on the network, but is associated with the active sockets actually present on the device, as they would be seen 'through' the Pi.
So far in addition to Proxy ARP, I have also got DNAT routing working with iptables, but I just can't figure out how to make it seem like the eth0-connected device is logically apart of the network along with its sockets. I can separately spoof ARP requests, or spoof raw tcp sockets, but I can't marry the two. It is critical that the Pi and this device appear as separate as possible in the network.
Could I somehow configure the Pi to vacillate the IP assigned to the wireless interface between its own IP and the device it is 'bridging' for? Or does the Raspberry Pi's lack of WDS support simply doom my efforts to achieve a pseudo-bridge with the above functionality using network/transport layer workarounds like this?
