How to allow NAT only when OpenVPN is connected on Ubuntu Server?

Question

openvpn

Good evening.
Task: route client traffic from the internal network through OpenVPN.

Right now I'm using the following rules:

sudo iptables -A FORWARD -o tun0 -i eth0 -s 192.168.1.0/24 -m conntrack --ctstate NEW -j ACCEPT
sudo iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -A POSTROUTING -o tun0 -t nat -j MASQUERADE

Faced with the fact that in the absence of a vpn connection, traffic starts to go through the usual one. Can you please tell me how to disable it?

Answer 1

iptables --policy FORWARD DROP