How to prevent leaks from VPN

I used following commands to prevent -almost- any outgoing internet connection from my Linux computer when VPN connection is not active. It is simple and it works.

Reset ufw rules to default
# ufw --force reset 

Drop all incoming traffic
# ufw default deny incoming 

Drop all outgoing traffic
# ufw default deny outgoing 

Let firewall allow outbound VPN traffic
# ufw allow out on tun0 

Let firewall allow VPN connection to be established
Change IP, port and protocol values as per your VPN server config
Example: ufw allow out to 255.255.255.255 port 9999 proto udp
# ufw allow out to $serverIP port $port proto $proto 

Run firewall and make it start automatically during startup
# ufw enable

Ertuğrul Harman

I’m a US-based software engineer with a background in law. I share practical tech notes here for my future self and anyone who finds them useful.
Current product: A privacy-focused, local-storage-only task manager with a built-in focus timer:
Masterlist: Focus & Tasks (App Store)