separate IP stacks?

Hi there!

I would like to set up a Linux box with multiple interfaces, on which I can more or less conveniently decide, which interface is used by a network application/daemon.

Target is, to have a client program running, using e.g. eth0 (ip 192.168.1.2) and a corresponding server listening at eth1 (ip 192.168.1.1), where traffic definetly leaves the box at eth0 and finally reaches eth1 via the network.

Ideally would be a solution where I simply launch a console window under X, set a environment variable to an network device name, and from there on all programs launched from that console are using that network interface and its (obviously necessary) uunshared IP stack.

Even better would be if this network interface separataion would take place on physical level, that if there are several VLAN (interfaces) configured for such a device, those share the IP stack.

Bottom line: I would like to have a linux box which kinda simulates separate network nodes, with being able to run all common network apps on those "devices" without changing the program code and with as less software overhead as possible (no virtual machines etc.)

Is there anything out there to set up such a scenario?

Thanx in advance

Harry