My last post was an year ago! Lot of things have happened in between. I had completed my Masters, majoring in Physics from IISERK, last May and have moved to Singapore to join the Centre for Quantum Technologies (CQT) at NUS for a PhD. My current work is on ultracold molecules, where we are aiming to probe quantum many-body physics in an ultracold Fermi-Fermi mixture of 40K and 6Li.
Enforcing an application, for example a torrent client like Transmission , to always use the VPN interface or any particular network interface for that matter, is trivially simple using iptables on Debian, Ubuntu or any other GNU/Linux distro. Personally, I am running Debian Sid on the Raspberry Pi . Occasionally I use it for downloading files ( legal stuff, seriously, believe me :D ) using Transmission Bittorrent client over a VPN connection. Sometimes it happens that the VPN connection fails and doesn't reconnect for whatever reason and Transmission continues pulling stuff directly over my internet connection, which I would like to avoid. Fortunately it is very straightforward to enforce rules based on application owner UID. Transmission runs under the owner debian-transmission in Debian (use htop to check this) and the following two lines of iptables ensures that any process with owner having UID, debian-transmission , will not use any other network interface apart from the