I have 2 network interfaces on my QNX target board, one is for ethernet interface with ip 10.10.1.220. The other one is 
modem interface with iP 172.16.1.2, which is a bridge to remote terminal, with modem interface IP of 172.16.1.1 and 
ethernet interface ip of 10.10.1.10.

So the communicaion is like this

10.10.1.220 -172.16.1.2  ...............bridge.................172.16.1.1-10.10.1.10

And by the way, 10.10.1.220 has subnet mask of 255.255.255.128 so that 10.10.1.10 ip does not fall under the same subnet


The remote terminal is a working system and my QNX target board needs to establish socket communication to remote 
terminal IP 10.10.1.10.

So I need to configure in my QNX to allow ethernet packet to be forwarded through modem interface. I know it can be done
 if I setup routing table like route -add 10.10.1.220 172.16.1.1. But such routing rule causes SOURCE IP in socket 
packets to be replaced (to modem interface ip). 

So my question is, how I might configure QNX such that ip packet from it's ethernent interface may be forwarded without 
having SOURCE IP being replaced?