I have a QNX device with 4 Ethernet interfaces and would like to set it up so the interfaces cannot bridge or share 
packets and each is able to have its own "default gateway".

What I am trying to accomplish is that any packet received on an interface is sent back out on that same interface no 
matter the network it came from. In normal circumstances, this works fine "out of the box" when the incoming packet 
arrives on the interface's own subnet. But, suppose the packet arrives via a router and is on a different network. 
Without a default gateway or static route defined, the QNX IP layer will toss the packet.

Does anyone have a good solution to this problem? I feel like I am overlooking something really simple.