How to Fix: iptables config blocks OpenVPN with udp error "Operation not permitted (code=1)

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OpenVPN issue with iptables configuration blocking UDP traffic.

The Problem

The 'Operation not permitted' error when using OpenVPN with UDP is frustrating and can be caused by various factors. This error occurs when the OpenVPN client tries to establish a connection through an iptables rule that doesn't allow it.This issue affects users who have set up their own OpenVPN server and are trying to connect to it using a client. The good news is that this problem has a solution, and we will walk you through it step by step.
💡 Why You Are Getting This Error

                The primary reason for the 'Operation not permitted' error is that the iptables rule is blocking the UDP packets sent by OpenVPN. This can happen if the rule is not properly configured or if there are other rules in place that interfere with it.Another possible cause of this error is that the Debian kernel version and iptables version are not compatible, which can lead to unexpected behavior.

            ✅ Best Solutions to Fix It

                Enabling the UDP Chain

                    Step 1: Open a terminal as the root user and run the command `sudo iptables -A INPUT -p udp -j ACCEPT` to add a new rule that allows UDP packets.Step 2: Next, run the command `sudo iptables -A OUTPUT -p udp -j ACCEPT` to allow UDP packets sent by OpenVPN to reach the internet.Step 3: Finally, run the command `sudo service iptables restart` to apply the changes and ensure they take effect.



                Removing the ICMP Rule

                    Step 1: Open a terminal as the root user and run the command `sudo iptables -D INPUT -p icmp -m state --state NEW -m icmp --icmp-type 8 -j ACCEPT` to remove the rule that allows ICMP packets.Step 2: Next, run the command `sudo iptables -D INPUT -p icmp -m state --state RELATED,ESTABLISHED       -j ACCEPT` to remove the rule that allows related and established ICMP packets.


            💡 Conclusion
            To resolve the 'Operation not permitted' error when using OpenVPN with UDP, you can try enabling the UDP chain or removing the ICMP rule. If neither of these methods work, it's possible that there are other issues at play, such as compatibility problems between the Debian kernel and iptables version. In this case, it may be necessary to consult the documentation for your specific setup or seek further assistance from a networking expert.

Full step-by-step guide with screenshots: Read the complete fix here

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