Learn how to troubleshoot and solve the common problem of OpenVPN clients not being able to access the internal network of the VPN server.
OpenVPN is a popular and secure VPN solution that allows you to create a private network over the internet. However, sometimes you may encounter a problem where your OpenVPN clients can connect to the VPN server, but cannot reach the internal network behind it. This can be frustrating and prevent you from accessing the resources you need. In this article, we will explain why this problem occurs and how to fix it using some simple steps.
Table of Contents
What Causes OpenVPN Clients Not to Reach the Internal Network?
There are several possible reasons why your OpenVPN clients cannot access the internal network of the VPN server. Some of the most common ones are:
- Incorrect routing configuration: The VPN server may not have the proper routes to forward the traffic from the VPN clients to the internal network, or vice versa. This can happen if you have multiple network interfaces on the server, or if you have a firewall or another router between the server and the internal network.
- Incorrect firewall rules: The VPN server or the internal network may have firewall rules that block or drop the traffic from the VPN clients. This can happen if you have a strict firewall policy, or if you have not allowed the VPN subnet or port in your firewall rules.
- Incorrect DNS settings: The VPN clients may not be able to resolve the hostnames of the internal network devices, or may use the wrong DNS servers. This can happen if you have not configured the DNS settings properly on the VPN server or the clients, or if you have a DNS conflict or cache issue.
How to Fix OpenVPN Clients Not Reaching the Internal Network?
To fix the problem of OpenVPN clients not reaching the internal network, you need to check and correct the following settings on the VPN server and the clients:
Solution 1: Routing configuration
You need to make sure that the VPN server has the correct routes to forward the traffic from the VPN clients to the internal network, and that the internal network devices have the correct routes to send the traffic back to the VPN clients. You can do this by using the route command on the VPN server and the clients, and by adding the push “route <internal network>” option in the server configuration file. For example, if your internal network is 192.168.1.0/24 and your VPN subnet is 10.8.0.0/24, you need to add the following line in the server configuration file:
push "route 192.168.1.0 255.255.255.0"
This will push the route to the VPN clients, so they know how to reach the internal network. You also need to make sure that the internal network devices have a route to the VPN subnet, either by adding it manually, or by using the VPN server as the default gateway.
Solution 2: Firewall rules
You need to make sure that the VPN server and the internal network devices allow the traffic from the VPN clients. You can do this by checking and modifying the firewall rules on the VPN server and the internal network devices, and by allowing the VPN subnet or port in the firewall rules. For example, if you are using iptables on the VPN server, you need to add the following rules to allow the traffic from the VPN clients:
iptables -A INPUT -i tun0 -j ACCEPT
iptables -A FORWARD -i tun0 -j ACCEPT
iptables -A OUTPUT -o tun0 -j ACCEPT
This will allow the traffic from the VPN interface (tun0) on the VPN server. You also need to allow the VPN port (1194 by default) on the internet interface of the VPN server, and the VPN subnet (10.8.0.0/24 by default) on the internal network devices.
Solution 3: DNS settings
You need to make sure that the VPN clients can resolve the hostnames of the internal network devices, and that they use the correct DNS servers. You can do this by configuring the DNS settings on the VPN server and the clients, and by using the push “dhcp-option DNS <DNS server>” option in the server configuration file. For example, if you want to use the VPN server as the DNS server for the VPN clients, you need to add the following line in the server configuration file:
push "dhcp-option DNS 10.8.0.1"
This will push the DNS server address to the VPN clients, so they can use it to resolve the hostnames of the internal network devices. You also need to make sure that the VPN server can resolve the hostnames of the internal network devices, either by using the internal DNS server, or by adding them to the /etc/hosts file.
Frequently Asked Questions (FAQs)
Question: How can I test if the VPN clients can reach the internal network?
Answer: You can use the ping or traceroute commands on the VPN clients to test the connectivity to the internal network devices. For example, if you want to ping the device with the IP address 192.168.1.10, you can use the following command:
ping 192.168.1.10
If you get a reply, it means that the VPN client can reach the device. If you get a timeout or an error, it means that there is a problem with the routing, firewall, or DNS settings.
Question: How can I troubleshoot the OpenVPN connection?
Answer: You can use the openvpn command with the -v or –verb option to increase the verbosity level of the OpenVPN logs. For example, you can use the following command to start the OpenVPN client with the highest verbosity level:
openvpn --config client.ovpn --verb 9
This will show you detailed information about the OpenVPN connection, such as the handshake, the encryption, the routing, and the errors. You can use this information to identify and fix the problem.
Question: How can I secure the OpenVPN connection?
Answer: You can use the following options to enhance the security of the OpenVPN connection:
- Use a strong encryption algorithm, such as AES-256-CBC, and a strong authentication method, such as TLS.
- Use a unique and secure certificate and key pair for each VPN client, and revoke them if they are compromised or no longer needed.
- Use a pre-shared key (ta.key) to protect against denial-of-service attacks and man-in-the-middle attacks.
- Use a firewall to restrict the access to the VPN port and subnet, and to block any unwanted or malicious traffic.
Summary
In this article, we have explained how to fix the common problem of OpenVPN clients not reaching the internal network of the VPN server. We have discussed the possible causes of the problem, such as incorrect routing, firewall, or DNS settings, and how to check and correct them. We have also provided some FAQs and tips to help you test, troubleshoot, and secure the OpenVPN connection. We hope that this article has helped you to solve the problem and to enjoy the benefits of OpenVPN.
Disclaimer: This article is for informational purposes only and does not constitute professional advice. We are not responsible for any damages or losses that may result from following the instructions or using the tools in this article. Please use them at your own risk and discretion.