Comment 5 for bug 578862

This seems to work in that it forces qbittorrent to use a specific network interface, however qbittorrent gets confused if there are multiple default gateways. For example, I have the following setup with qbittorrent locked to the wlan0 interface:

     $ route -n
     Kernel IP routing table
     Destination Gateway Genmask Flags Metric Ref Use Iface
     192.168.3.0 0.0.0.0 255.255.255.0 U 2 0 0 wlan0
     192.168.2.0 0.0.0.0 255.255.255.0 U 1 0 0 eth0
     169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 eth0
     0.0.0.0 192.168.2.1 0.0.0.0 UG 0 0 0 eth0
     0.0.0.0 192.168.3.1 0.0.0.0 UG 0 0 0 wlan0

One would think since qbittorrent is limited to the wlan0 interface, it would also use 192.168.3.1 as its default gateway. It does not, and still tries to connect on 192.168.2.1. This means that with the above routing table, qbittorrent actually stalls all torrent activity. Deleting the eth0 default gateway causes all internet traffic to go through the wlan0 interface, including qbittorrent.

It's nice that qbittorrent refuses to use eth0 when configured to use wlan0, but I'd prefer if I could have both enabled and send qbittorrent (and a few other apps) down wlan0 with everything else defaulting to eth0.