Vuze torrent client includes IP-Bind feature which can bind itself to a specific interface for downloading. If the specified interface is disconnected or unavailable , it will stop all downloads and wait until the connection becomes available again. This is very important feature to prevent your real IP address from leaking incase of unexpected network disruption. 

Step 1. Open Vuze client > Tools > Options > Mode and change User Proficiency to "Advanced"

Step 2.  Click on Advanced Network Settings under Connection tab and look for "SwitchVPN Tap Adapter" Interface number ( example eth6 )
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Step 3. Scroll down and Check "Enforce IP bindings even when interfaces are not available, prevents any connections if none of the specific interfaces are available"
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Thats all! Now Vuze will only start downloading if the VPN is connected, It will halt all the downloads immediately as soon as you disconnect the VPN, thus making sure there are no IP leaks.

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