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

E. Harman

From defending clients to defending code. Developing software professionally in the U.S., offering legal advice on the side, and gaming like it’s still the ’90s. LLM Exeter, PhD(c) in Private Int’l Law. Defender of Kaer Morhen.