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I have two NIC's (one Ethernet and one tethering from mobile). My Ethernet internet connection is port filtered, so I can't use some applications on that. All applications can run on my mobile tethering, but as I have only limited data I only want some selected applications to use that NIC.
So the question is: how can I force only some process to use a specific NIC?
Basically you want to "jail" your process and force it to bind to a specific NIC. Lots of people use LD_PRELOAD but LD_PRELOAD does not control the route that the processes uses. It will use the first route. One possible resolution was on SuperUser https://superuser.com/questions/241178/how-to-use-different-network-interfaces-for-different-processes/241215#241215
ip netns can do this.
TL;DR: Create network namespaces, associate interfaces to them and then run "ip netns exec NAME cmd..."
Just check if your distro supports ip netns... (Backtrack 5r3 does not, whereas Kali does ;) )
IN MORE DETAILS:
#create netns
ip netns add myNamespace
#link iface to netns
ip link set eth0 netns myNamespace
#set ip address in namespace
ip netns exec myNamespace ifconfig eth0 192.168.0.10/24 up
#set loopback (may be needed by process run in this namespace)
ip netns exec myNamespace ifconfig lo 127.0.0.1/8 up
#set route in namespace
ip netns exec myNamespace route add default gw 192.168.0.1
#force firefox to run inside namespace (using eth0 as outgoing interface and the route)
ip netns exec myNamespace firefox
