Route specific program to specific NIC

Question

I have two internet connection, One internet connection has very high latency, it has fluctuation in connection (there is a tree between tower & Wifi CPE, so signal goes up & down) but its fine for downloading as connection never goes to 0. Another one is landline connection, they have strong download limit.

So what i want is to use wlan0 for few specific programs like, steam & downloading etc. basically program which consume lot of data.

And i want to use wlan1 for browsing & other stuffs, less data.

In short, I want to route specific programs though specific NIC, I don't have specific range of IP's.

I can connect both of them through wifi as i have 1 extra wifi adapter (wlan0,wlan1), as another option i can connect one with ethernet (wlan0,eth0)

Answer 1

It could be possible if your process has something iptables can match against, such as a specific group. For example, given a group to-wifi, you could have iptables rules like so:

iptables -A FORWARD --in-interface wlan0 -j ACCEPT
iptables -t nat -A OUTPUT -m owner --gid-owner to-wifi --out-interface wlan0 -j MASQUERADE  

(And with forwarding enabled: sysctl -w net.ipv4.conf.all.forwarding=1.)

Then, if you run, for example, Steam thus:

sg to-wifi steam

Any traffic from that Steam process (+ any child processes) will be forwarded from whichever interface it was heading through to the wireless interface.

I have never tried interface-to-interface redirection, but I have used iptables to redirect all TCP traffic from Steam to a proxy by matching against groups, so these rules may not be enough by themselves.

---

This could be accomplished by creating groups for each interface and adding yourself to them. For example, using the addgroup and adduser commands:

sudo addgroup to-wifi
sudo adduser $USER to-wifi
sudo addgroup for-eth0
sudo adduser $USER for-eth0

You need to re-login for your new group memberships to take effect.

Related:

• Forwarding traffic between 2 interfaces
• iptables forward all traffic to interface
• iptables forwarding between two interfaces
• How to forward packets between two interfaces?

Answer 2

As far as I know, there is no way to do that.

This can be done with iptables rules on the specific ports + destinations they use to make their connections, but I'm not aware of a local way to do it.