Goal: configure Ivacy VPN service on Windows in such way that only select few applications (QBittorrent in my case) would use it.
After several hours of bashing my head against the wall, here is what I found.
Problems:
1) There is a
guide describing how to achieve this with OpenVPN; however, I found that, for some reason, with Ivacy this yields a much worse performance than when connecting with Ivacy's proprietary client. Namely, QBittorrent is able to connect to much fewer peers. Ivacy's support has (so far) been unable to solve this.
2) QBittorrent allows one to configure the network interface through which to connect, but the drop-down list does not include "Ivacy" - the name of the VPN interface created by Ivacy's proprietary client.
Solution:
1)
Set up the Windows Firewall rules to block all communication for QBittorrent, except through the VPN interfaces. This is a safety measure, not required for the rest to work.
2) Download and install
ForceBindIP.
3) Connect to the VPN. Find out the GUID of the VPN network interface: open regedit and browse to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces.
4) Modify QBittorrent's shortcut as follows:
-i
P.S. Of all Torrent clients I tried, only Vuze was able to handle this properly. However, its GUI is extraordinarily repulsive and inconvenient, not to mention the ads.