Kill switch : should I buy a router ?

[temperdu 4]

I'm currently running transmission (port 5743) on a Synology (LAN IP 192.168.1.11). I've setup OpenVPN on the Syno and I'm using port forwarding (port 80) on the router side (LAN IP 192.168.1.254) to let the Syno answer to HTTP requests aimed at my home IP. I would like to prevent any transmission trafic when AirVPN is down, yet letting the Syno connected to the internet for other usage (like HTTP typically).

 

I've read about kill switches implemented  with static routes on the router side (DD-WRT, Tomato, OpenWRT), aimed at a particular machine. But I'm afraid it doesn't suit my usecase since it would block it would block all the trafic and not only transmission. Is there an easy way to tune things more precisely than just by IP on my LAN ? If I mean "easy", it is because my knowledge is actually limited. If I've used words like "static route" or such, don't get me wrong : I actually don't fully understand what is behind such words.

 

Is a router the place to setup things, or is there a way to implement such a selective kill switch on a Synology ?

[OpenSourcerer 1435]

The only way is to do it in Transmission: Connect to AirVPN and bind Transmission to either the tunnel interface (preferred and recommended, if possible) or to its IP (since it changes, it's more of a burden). I don't have a Synology NAS to test and tell you how to do that, though, but it's what I do in qBittorrent - no traffic without a working tun0 interface.

[temperdu 4]

Thanks for the input. Any idea about how to setup transmission (config files ?) so as to bind it to tun0 ?

[OpenSourcerer 1435]

Like I said, I have no idea how to do that with Synology's Transmission app.

You could try accessing the web UI of the transmission-daemon which should listen on your.synology.nas.ip:9091.

You could also try it with transgui, a cross-platform remote GUI for Transmission.

Lastly, maybe the Synology app provides some kind of configuration interface which you can take advantage of.

 

In all cases, look for a setting to bind Transmission to something (IP/tun0/tunnel/VPN connection/something else), it should always be in the advanced settings.