How to prevent IP leak on Linux when OpenVPN fails to connect to the server while I am surfing on the net?
I read about kill switch, but after some internet searches I found out that is not implemented in OpenVPN.
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Sign up to join this communityHow to prevent IP leak on Linux when OpenVPN fails to connect to the server while I am surfing on the net?
I read about kill switch, but after some internet searches I found out that is not implemented in OpenVPN.
Unfortunately, the previous (since deleted) answer is incorrect and will allow deanonymization because it allows any connection over port 1194, not just traffic originating from OpenVPN. You should use a simpler firewall which does nothing more than block all non-OpenVPN client output to the outside.
If you do not have an openvpn
group, create it. The -r
makes it a system group.
groupadd -r openvpn
Once it exists, add this line to your OpenVPN configuration file to run with this group.
group openvpn
Now you can set the firewall to block output for all processes other than the OpenVPN client. You do not need to specifically whitelist any ports, just the correct group and the TUN device.
# Flush the tables. This may cut the system's internet.
iptables -F
# Let the VPN client communicate with the outside world.
iptables -A OUTPUT -j ACCEPT -m owner --gid-owner openvpn
# The loopback device is harmless, and TUN is required for the VPN.
iptables -A OUTPUT -j ACCEPT -o lo
iptables -A OUTPUT -j ACCEPT -o tun+
# We should permit replies to traffic we've sent out.
iptables -A INPUT -j ACCEPT -m state --state ESTABLISHED
# The default policy, if no other rules match, is to refuse traffic.
iptables -P OUTPUT DROP
iptables -P INPUT DROP
If everything worked, you should now have access to the internet only through your VPN. You may need to make some tweaks depending on your particular setup (for example, if you need access to other devices on your local network), but this should be a general solution. In order to make these changes persistent, follow your distribution's instructions on saving firewall settings.
Please understand that VPNs are not designed for privacy or anonymity. Even when using a proper firewall, there are countless ways to circumvent its supposed protections, even if the VPN claims not to keep logs. If you need actual anonymity, you should instead use something like Tor.
sudo openvpn 'Austria.ovpn'
- which is a config file to which I prepended group openvpn
. Must I reboot? Because if I reboot the iptables reset, but I don't want to try to make them permanent if they might brick my internet :)
– Spectraljump
Dec 9 '18 at 13:20
iptables-save
(using sudo apt-get install iptables-persistent
) and I restart, it's the same as before I restart: I can connect to my LAN & have no access to internet. But I can't establish any openvpn connection: cannot resolve host address my.vpn.domain:Port
& could not determine IPV4/IPv6 protocol
. I give up for now, I have no clue what further rabbit holes to go through to debug this overcomplicated stuff that should just be built in <_<. Oh, and sudo iptables -P OUTPUT REJECT
throws iptables: Bad policy name
- I tried DROP instead & also tried not adding that rule.
– Spectraljump
Dec 9 '18 at 14:22
openvpn
group? If it is, then it should not be getting blocked by the firewall. If it is not, then that would explain the issue.
– forest
Dec 10 '18 at 8:15
openvpn
after the VPN tunnel is established, hence your openvpn client cannot resolve the hostname of your openvpn server. You will need to either specify the IP address (instead of the hostname) of your openvpn server, or make sure that DNS resolution is allowed by the firewall.
– ema
Jul 9 '19 at 21:42