Multiple Ethernet Interfaces - How to create a separate network and access from C code

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http://stackoverflow.com – I have a Linux device (actually a BeagleBoard for the prototype) with two Ethernet adapters. What I want is this: Primary ethernet interface (eth0) connects to a client's network (may be DHCP or assigned a static IP). Second ethernet interface (eth1) connects directly to another Linux board. User-level C programs on the Beagle can listen for incoming connections from the client's network (on eth0), respond as required, and possibly connect to the other device on eth1 We want the second device to be completely hidden from the rest of the network, so that only programs on the Beagle can con (HowTos)