It's been complained about in the forum the instructions on setting up a DD-WRT router with airvpn located at https://airvpn.org/ddwrt/?hl=ddwrt is out of date. For the DD-WRT release I use, the guide is indeed a little outdated, but comprehensible.   Still, without warranty and strictly on your own responsibility you could try my guide below. I am unable to provide any support, but this guide hopefully can help someone.   For this guide I presume you know what a kill switch is, you know how to