#1 By injecting a custom library

We can use ld_preload function to force the interface gateway with App-Route-Jail

Step 1: the gateway

We need to find what gateway the network interface is using then force that gateway to our jailed application and thus force the application to bind to a specific network interface

• How to find the interface gateway (there are many solution to find the gateway here are some commands that permit to find the used gateway)

$ route
$ route -n
$ ip rule list
$ ip route show
$ netstat -rn
$ cat /etc/network/interfaces
$ cat /etc/sysconfig/network-scripts/ifcfg-eth0
$ traceroute www.google.com
$ ip route show 0.0.0.0/0 dev eth0

Step 2: per application gateway

• Build App-Route-Jail

git clone https://github.com/Intika-Linux-Network/App-Route-Jail.git
cd Approute-Utils
chown 755 make.sh
./make.sh

• Add a route for the future marked packets (for the jailed application) in this example 192.168.1.1 is used as the forced gateway, this route rule wont affect other applications, this manipulation have to be done only once at the system boot for instance if you want to use this solution daily

ip rule add fwmark 10 table 100
ip route add default via 192.168.1.1 table 100

• Start the application that you want to jail

MARK=10 LD_PRELOAD=./mark.so firefox

• Testing the wan IP address

MARK=10 LD_PRELOAD=./mark.so wget -qO- ifconfig.me

#2 By using the Kernel’s namespace feature through firejail

Firejail https://firejail.wordpress.com/ can force an application to use a specific network, like the following example:

firejail --dns=8.8.8.8 --net=eth0 --ip=192.168.1.1

#3 Alternative:

Additional information on the matter are availables on this SU QA.