routing based on interface used?

Question

I have two internet connections. Default eth0 and a vpn tunnel on tun0.

my ip show route shows:

default via 149.202.xxx.xxx dev eth0
10.8.8.0/24 dev tun0  proto kernel  scope link  src 10.8.8.234
149.202.xxx.0/24 dev eth0  proto kernel  scope link  src 149.202.xxx.yy

Gateway for tun0 is 10.8.8.1 although I dont want to set it up as default. What I would like to do is for example use ping -I tun0 8.8.8.8, or curl --interface tun0 http://somewebsite.com and in this particular situation I would like to use tun0 as my outgoing connection.

Is it possible?

Answer 1

This is what worked for me:

echo "10 vpn" >> /etc/iproute2/rt_tables
ip route add default via 10.8.8.1 dev tun0 table vpn
ip rule add from 10.8.8.234/32 table vpn
ip rule add to 10.8.8.1/32 table vpn
ip route flush cache

And proof:

$ curl ifconfig.co
149.202.xxx.xxx

$ curl --interface tun0 ifconfig.co
178.250.xxx.xxx